Lattice2010

14 Jun 2010, 08:30 → 19 Jun 2010, 18:00 Europe/Rome

Villasimius, Sardinia

THE XXVIII INTERNATIONAL SYMPOSIUM ON LATTICE FIELD THEORY LATTICE 2010 WEB PAGE: http://www.infn.it/Lattice2010 The LATTICE 2010 conference will take place from June 14-19 at the Tanka Village Resort, Villasimius, Sardinia, Italy.

Slides lee.pdf

Monday, 14 June

Welcome

slides martinelli_lattice2010.pdf

Session 1

1 Topology, the Wilson Flow & the HMC Algorithm

Speaker: Martin Luscher

Slides luscher.pdf

2 Hadron spectrum on the lattice

Speaker: Christian Holbling

Slides hoelbling.pdf

10:00 Coffee break

Session 2

3 Hadron structure & form factors

Speaker: Constantia Alexandrou

Slides dina.alexandrou.pdf

4 Towards four flavor dynamical simulations

Speaker: Gregorio Herdoiza

Slides herdoiza.pdf

11:30 Lunch and other activites

Parallel 01: Hadronic structure and interactions

5 Nucleon form factors and structure functions from Nf=2 clover fermions

We present an update on the ongoing efforts of the QCDSF collaboration to compute the nucleon's generalized) form factors and moments of structure functions. The focus will be on our most recent results obtained on gauge configurations where the pseudo-scalar meson mass is in the range of 170-270 MeV. We will compare our results with calculations carried out in chiral effective theories.

Speaker: Dirk Pleiter (DESY)

Slides pleiter.pdf

6 Systematic errors in extracting nucleon properties from lattice QCD

Form factors of the nucleon have been extracted from experiment with high precision. However, lattice calculations have failed so far to reproduce the observed dependence of form factors on the momentum transfer. We have embarked on a program to thoroughly investigate systematic effects in lattice calculation of the required three-point correlation functions. In this talk we focus on the possible contamination from higher excited states. We present a new method which is designed to suppress excited state contributions and test it effectiveness for several baryonic matrix elements, different lattice sizes and pion masses.

Speaker: Bastian Knippschild (university of mainz)

Slides knippshild.pdf

7 Hadron Form Factors at Large Transfer Momentum (I)

We report a recent breakthrough in lattice QCD calculations of hadron form factors at large momentum transfer. Conventional lattice form-factor calculations typically reach about 2.5 GeV$^2$ or less, but in this work the transfer momentum is pushed as high as 6 GeV$^2$. Our approach can be applied to isotropic lattices and lattices with smaller lattice spacing to calculate even larger-$Q2$ form factors. We will discuss the methodology and demonstrate results for the nucleon and pion from 2+1-flavor anisotropic clover lattices. These measurements could give important theoretical input to experiments, such as those of JLab's 12-GeV program, and provide insight into hadronic structure.

Speaker: Saul Cohen (Boston University)

Slides cohen.pdf

8 Axial and pseudoscalar form-factors of the Delta baryon

We discuss results on the axial and pseudoscalar Delta form factors. We first test the lattice set-up in the quenched approximation and present first results with a hybrid action using a staggered sea and domain-wall valence fermions.

Speaker: Eric Gregory (University of Cyprus)

Slides gregory.pdf

9 Hyperon Form Factors from N_f=2+1 QCD

We present results from the QCDSF collaboration for the electromagnetic and semi-leptonic form factors for the hyperons. The simulations are performed on our new ensembles generated with 2+1 flavours of dynamical O(a)-improved Wilson fermions. A unique feature of these configurations is that the quark masses are tuned so that the singlet quark mass is held fixed at its physical value. We use 5 such choices of the individual quark masses on 24^3x48 lattices with a lattice spacing of 0.083fm.

Speaker: James Zanotti (University of Edinburgh)

Slides Zanotti.pdf

Parallel 03: Nonzero temperature and density

10 The finite temperature QCD transition

We extend our previous two studies on the finite temperature cross-over of QCD. We chose even finer lattices ($N_t$=16) and work with physical quark masses. The new results are in complete agreement with our earlier ones. We compare our findings with the published results of the hotQCD collaboration (obtained with the asqtad and p4 actions with $N_t = 8$). All these results are confronted with the predictions of the Hadron Resonance Gas model and Chiral Perturbation Theory, both with the physical and with a modified spectrum which takes into account lattice discretization effects.

Speaker: Zoltan Fodor (University of Wuppertal)

Slides fodor.pdf

11 The QCD equation of state with dynamical quarks

We determine the equation of state of QCD from lattice simulations. Lattices with Nt = 6 and 8 are used, and the continuum limit is approached by checking the results at Nt = 10 and 12. A Symanzik improved gauge and a stout-link improved staggered fermionic action is utilized; the light and strange quark masses are set to their physical values.

Speaker: Szabolcs Borsanyi (University of Wuppertal)

Slides borsanyi.pdf

12 On the universal O(N) scaling behavior of (2+1)-flavor QCD

We analyze the universal scaling behavior of (2+1)-flavor QCD in terms of various scaling functions corresponding to the magnetic equation of state, the specific heat and generalized quark number susceptibilities. Lattice simulations on Nt=4 and Nt=8 lattices with improved staggered fermions within a wide range of quark masses have been performed and are fitted to the scaling functions. In general we find good agreement with O(N) universal scaling for light quark masses which are smaller or about the physical masses. The scaling naturally includes Goldstone behavior in the chiral condensate.

Speaker: Christian Schmidt (Frankfurt Institute for Advanced Studies)

Slides schmidt_lat10.pdf

13 Chiral Aspects of Improved Staggered Fermions with 2+1-Flavors from the hotQCD Collaboration

We present recent results from HotQCD simulations of 2+1 flavors of improved staggered fermions at zero baryon number density near the high temperature crossover. Included are new results from simulations of asqtad fermions at Nt = 12 and a nearly physical Goldstone pion mass and from simulations of HISQ fermions at Nt = 8. We focus on observables sensitive to chiral symmetry and confinement. A companion HotQCD talk discusses the effects of staggered-fermion taste-symmetry breaking on thermodynamic quantities.

Speaker: Wolfgang Soeldner (GSI Darmstadt)

Slides soldner.pdf

14 Taste symmetry and QCD thermodynamics with improved staggered fermions

Taste symmetry violations in staggered fermion formulations correlate strongly with the cut-off (lattice spacing) dependence in physical observables. Better taste symmetry on the lattice can be achieved either by decreasing the lattice spacing and going to larger temporal extent in finite-temperature calculations, or by further improving the action. The Highly Improved Staggered Quark (HISQ) action offers further degree of improvement and substantially reduces taste violations. We report on our studies of the 2+1 flavor QCD thermodynamics with HISQ. By systematically comparing HISQ, asqtad, p4 and stout calculations we quantify how the cut-off effects manifest themselves in different physical observables, including the renormalized Polyakov loop, chiral condensate, various fluctuations and correlations of conserved charges. The implications for the equation of state and comparison to the Hadron Resonance Gas model are also discussed. The chiral aspects of the QCD transition are discussed in a separate HotQCD presentation by W. Soeldner.

Speaker: Alexei Bazavov (University of Arizona)

Slides bazavov_slides.pdf

Parallel 05: Vacuum structure and confinement

15 Lattice QCD Study for Gluon Propagator and Gluon Spectral Function

The gluon propagator is studied in the Landau gauge in SU(3) lattice QCD at beta=5.7, 5.8 and 6.0 at the quenched level. Through the functional-form analysis of the gluon propagator obtained in lattice QCD, we find that the Landau-gauge gluon propagator is well described by the Yukawa-type function e^{-mr}/r with m=600MeV for r=0.1-1.0fm in the four-dimensional Euclidean space-time [1]. Associated with the Yukawa-type gluon propagator, we derive analytical expressions for the effective mass and the spectral function rho(omega) of the gluon field [1]. As a remarkable fact, the obtained gluon spectral function rho(omega) is almost negative definite, except for a positive delta-functional peak at omega=m. We also investigate the relevant gluonic energy scale for the effective gluon mass using the new lattice technique in Ref.[2]. References [1] T. Iritani, H. Suganuma and H. Iida, Phys. Rev. D80, 114505 (2009). [2] A. Yamamoto and H. Suganuma, Phys. Rev. Lett. 101, 241601 (2008); Phys. Rev. D79, 054504 (2009); Phys. Rev. D81, 014506 (2010).

Speaker: Hideo Suganuma (Department of Physics, Kyoto University)

Slides Suganuma.pdf

16 Lattice QCD analysis for the instantaneous interquark potential in the generalized Landau gauge

We analyze the instantaneous interquark potential in the generalized Landau gauge (lambda gauge) in SU(3) lattice QCD. Using this gauge, we can analyze continuous change of gluon properties from the Landau gauge toward the Coulomb gauge. In the Coulomb gauge, the instantaneous potential is expressed by the Coulomb plus linear potential, with about two times larger string tension. In the Landau gauge, the instantaneous potential has no linear part. We find that this linear confinement part appears and grows during the change from the Landau gauge to the Coulomb gauge. We also find that the linear derivative of the instantaneous potential coincides with the string tension in a specified lambda gauge with lambda_C. In this gauge, the interquark potential can be approximately described by the instantaneous gluon exchange. We expect that this lambda_C gauge is useful in connecting from QCD to the quark model.

Speaker: Takumi Iritani (Kyoto University)

Slides iritani.pdf

17 Relevant momentum components of gluons for confinement and chiral symmetry breaking

We investigated which momentum components of gluons induce confinement and chiral symmetry breaking in lattice QCD. For this purpose, we formulated a new framework to introduce the momentum cutoff to the link variable. We found that confinement and chiral symmetry breaking are induced by different momentum components of gluons.

Speaker: Arata Yamamoto (Kyoto University)

Slides Yamamoto.pdf

18 The glueball spectrum at large N

Using variational techniques, we measured the masses of the ground-state glueballs and some of their excitations in all the irreducible representationsof the cubic group in SU(N) gauge theories for N ranging from 3 to 8,at fixed lattice spacing in the scaling region, where some features of the continuum spectrum are already manifest. For this calculation, we developed an automated method for generating traced loops in all irreducible representations of the cubic group starting from a given closed path; this enabled us to extract glueball masses from a variational basis typically consisting of 40-60 trial operators. Our data show that there is a mild $N$-dependence of the spectrum, with a modest $1/N^2$ correction, confirming earlier large-$N$ results on a much wider portion of the low-energy spectrum. Our authomated method for constructing trial operators allows us to address directly the issue of mixing with scattering and torelon states.

Speaker: Enrico Rinaldi (SUPA, School of Physics and Astronomy, University of Edinburgh)

Slides Rinaldi.pdf

19 Can Lorentz-breaking fermionic condensates form in large N strongly-coupled LGT?

The possibility of Lorentz symmetry (spontaneous) breaking (LSB) has attracted considerable attention in recent years for a variety of reasons, including the attractive prospect of the graviton as a Goldstone boson. Though a number of effective field theory analyses of such phenomena have recently been given it remains an open question whether they can take place in an underlying UV complete theory. Here we consider the question of LSB in large N lattice gauge theories in the strong coupling limit. We apply techniques that have previously been used to correctly predict the formation of chiral symmetry breaking condensates in this limit. Generalizing such methods to other composite operators we find that certain LSB condensates can indeed form. In addition, the interesting possibility arises of condensates that 'lock' internal with external symmetries. The implications of such phenomena for the construction of quantum gravity theories are briefly discussed.

Speaker: Terry E Tomboulis (UCLA Department of Physics)

Slides tomboulis.pdf

Parallel 07: Standard model parameters and renormalization

20 Matching the lattice coupling to the continuum for the tree level Symanzik improved gauge action

The Numerical Stochastic Perturbation Theory project dealing with renormalization constants for the tree level Symanzik improved gauge action aims at three loop accuracy. To get this, one important ingredient is the two loop matching of the lattice coupling to continuum. We discuss how we get it, trying to emphasize the general strategy underlying the computation.

Speaker: Michele Brambilla (Parma University and INFN)

Slides Brambilla-MatchingMS2TLS.pdf

21 Renormalization constants for Wilson fermion lattice QCD with four dynamical flavours

We report about an ongoing non-perturbative computation of RI-MOM scheme renormalization constants for the lattice action with Iwasaki glue and four dynamical flavours currently in use by ETMC. For this goal dedicated simulations with four degenerate sea quark flavours are performed at several values of the standard and twisted quark mass parameters. We discuss a method for removing possible O(a) artifacts at all momenta and extrapolating renormalization constant estimators to the chiral limit. We give preliminary results at one lattice spacing.

Speaker: David Palao (INFN Sezione Tor Vergata)

Slides palao.pdf

22 Non-perturbative renormalization of quark mass in Nf=2+1 QCD with the Schroedinger functional scheme

We present an evaluation of the quark mass renormalization factor for Nf=2+1 QCD. The Schroedinger functional scheme is used as the intermediate scheme. The regularization independent step scaling function of the quark mass is evaluated in the continuum limit. The pseudo scalar density and the axial vector current renormalization factors are derived for the same action and the bare couplings as two recent large scale Nf=2+1 simulations of the CP-PACS/JL-QCD collaboration and that of PACS-CS collaboration. The quark mass renormalization factor is evaluated to renormalized bare PCAC masses in these simulations.

Speaker: Yusuke Taniguchi (University of Tsukuba)

Slides taniguchi.pdf

23 Perturbative vs non-perturbative renormalization: the case of the quark mass

Comparing perturbative and non-perturbative results for renormalization constants has been an issue for a while. The quark mass renormalization constant is a prototype example: discrepancies between different results have been several times ascribed to this issue. Given the logarithmic nature of the divergence, there is no theoretical obstruction to a perturbative computation. The problem, as it is well known, is how to perform the computation at high loops. Truncation errors should in turn be compared to a variety of errors (e.g. irrelevant effects, chiral extrapolation, finite size) which should be carefully assessed as well. We present our new results from Numerical Stochastic Perturbation Theory, in particular for the tree level Symanzik improved gauge action at n_f=2. The goal is to take all the sistematic effects under control at three loop level.

Speaker: Francesco Di Renzo (University of Parma and INFN)

Slides direnzo.pdf

24 Egalitarian Improvement to Democracy in Non-Perturbative Renormalization of Quark Operators

We present our results on non-perturbative renomalization of quark operators. Based on Nf=2 ETMC lattices we calculate vertex functions and propagators, and combine them using irreducible representation of the discrete rotational group H4. We test the running of these quantities including a possible non-perturbative contribution via Wilson operator expansion. This allows for the better computation of non-perturbative correction to the renormalized Z_q.

Speaker: Konstantin Petrov (Laboratoire de Physique Theorique)

Slides petrov.pdf

Parallel 09: Hadron spectroscopy

25 Chiral properties of light mesons in the $N_f=2+1$ overlap OCD

We summarize the project of the light meson spectrum with $N_f$=2+1 overlap fermions by JLQCD and TWQCD. We study the finite size effect by directly comparing results from two different lattice volumes. Through the chiral extrapolation carried out with additional data points with $m_{ud} = m_s$, we test the prediction of chiral perturbation theory.

Speaker: Junichi Noaki (KEK)

Slides noaki.pdf

26 Lattice QCD with optimal domain-wall fermions: light meson spectroscopy

We give an overview of our simulations of 2-flavors and (2+1)-flavors QCD with optimal domain-wall fermions, using a GPU cluster with 200 Tflops(peak)/36 Tflops(sustained). We work on a lattice of size $ 16^3 \times 32 $, with lattice cutoff $ a^{-1} \simeq 1.6 $ GeV, and eight dynamical (sea) quark masses in the range $ m_s/8 - m_s $, where $ m_s $ is the physical strange quark mass. The exact chiral symmetry on the lattice is preserved with $ N_s = 16 $ in the fifth dimension. We present our first results of light meson masses and decay constants.

Speaker: Ting-Wai Chiu (National Taiwan University)

Slides chiu.pdf

27 Light hadrons from Nf=2+1+1 dynamical twisted mass fermions

We present results from simulations performed by ETMC using $2+1+1$ flavours of twisted mass fermions at maximal twist. We concentrate on one value of the lattice spacing of $a\approx 0.078$fm, but we add first data at a second value of $a=0.06$fm to test for the size of lattice artefacts. The quark mass dependence of light meson masses and decay constants will be confronted to chiral perturbation theory. We will also discuss the K and D-meson masses. Using several lattice sizes as well as different values of the light, strange and charm quark masses we will make an attempt to assess systematic effects affecting our results.

Speaker: Siebren Reker (University of Groningen)

Slides reker.pdf

28 Pseudoscalar Decay Constants from $N_f=2+1+1$ twisted mass lattice QCD

We present first results for the pseudoscalar decay constants $f_K$, $f_D$ and $f_{D_s}$ in lattice QCD with dynamical up, down, strange and charm quark flavours. The investigation is based on gauge configurations generated by the ETM collaboration using $N_f=2+1+1$ Wilson twisted mass fermions at maximal twist at one value of the lattice spacing around 0.08 fm and several values of the light quark masses. In the valence sector the so called Osterwalder-Seiler formulation is used. The extra- and interpolation in the various quark masses will be discussed.

Speaker: Carsten Urbach (HISKP, Uni Bonn)

Slides urbach.pdf

Parallel 11: Chiral symmetry

29 The Aoki phase revisited

Continuing with the work exposed in the last lattice conference [Phys.Rev.D79:014509,2009, PoS(LAT2009)068], and in order to distinguish between the two different scenarios proposed by us and Sharpe [Phys.Rev.D79:054503,2009], we present data of simulations of QCD with two flavours of dynamical Wilson fermions, inside the Aoki phase and without an external source $\bar\psi\gamma_5\tau_3\psi$. Two different algorithms, MFA and the hybrid montecarlo, were used, and a consistency check was performed. During the simulations we measured, using the P.D.F. (probability distribution function) formalism, the second moment of the relevant order parameters of the Aoki phase, namely $\langle\left(i\bar\psi\gamma_5\psi\right)^2\rangle$ and $\langle\left(i\bar\psi\gamma_5\tau_3\psi\right)^2\rangle$. These numerical results allow us to improve our understanding of the Aoki phase.

Speaker: Alejandro Vaquero (Universidad de Zaragoza)

Slides vaquero.pdf

30 Wilson Fermions, Random Matrix Theory and the Aoki Phase

The QCD partition function for the Wilson Dirac operator, $D_W$, at finite lattice spacing $a$ can be expressed in terms of a chiral Lagrangian as a systematic expansion in the mass, the momentum and $a^2$. Starting from this chiral Lagrangian we obtain an analytical expression  for the spectral density of $\gamma_5 D_W$ in the microscopic domain (also known as the $]epsilon$-domain). It is shown that the $\gamma_5$-Hermiticity of the Dirac operator necessarily leads to the sign of  the coefficient of the $a^2$ term that allows an Aoki phase. The transition to the Aoki phase is explained in detail,  and the interplay of topological charge and finite $a$ is discussed. Finally, we formulate a random matrix theory for the Wilson Dirac operator in the sector of topological charge $\nu$. It is shown by an explicit calculation that this random matrix theory reproduces the $a^2$-dependence of the chiral Lagrangian in the microscopic domain and that the sign the $a^2$-term is directly related to the $\gamma_5$-hermiticity of $D_W$.

Speaker: Jacobus Verbaarschot (Stony Brook University)

Slides verbaarschot.pdf

31 Spectra of the Wilson Dirac operator for QCD with dynamical quarks

The spectrum of the Wilson Dirac operator for $N_f=1$ in the microscopic ($\epsilon$) regime including order $a^2$ corrections is discussed. Exact results are obtained from Wilson chiral Perturbation Theory in sectors of fixed topology. Topology is defined as the number of real eigenvalues of the Wilson Dirac operator. We compute the density of these real modes as well as the microscopic spectral density of the hermitian Wilson Dirac operator. We show how the change of sign of the Wilson fermion determinant associated with the real modes crossing the origin affects the average spectral properties of the Wilson Dirac Operator.

Speaker: P.H. Damgaard (The Niels Bohr Institute)

Slides damgaard.pdf

32 Mixed action computations on fine dynamical lattices

We report on our simulations with Neuberger valence fermions on CLS Nf=2 configurations with non perturbatively O(a) improved Wilson sea quarks. We consider the matching of QCD to ChPT in the so called mixed regime in which the sea quarks are in the p-regime while the valence quarks are in the p or in the epsilon regime.

Speaker: Fabio Bernardoni (Universidad de Valencia)

Slides bernardoni.pdf

33 Overlap Valence Quarks on a Twisted Mass Sea

We present the results of an investigation of a mixed action approach of overlap valence and maximally twisted mass sea quarks. Employing a matching condition on the pion mass, we analyze the continuum limit scaling of the pion decay constant and the role of chiral zero modes of the overlap operator in this process. We employ gauge field configurations generated by the European Twisted Mass Collaboration with linear lattice size L ranging from 1.3 to 2fm. The continuum limit is taken at a fixed value of L=1.3fm, employing three values of the lattice spacing and two values of the sea-sea pion mass.

Speaker: Krzysztof Cichy (Adam Mickiewicz University, Faculty of Physics)

Slides cichy.pdf

16:10 Coffee break

Parallel 02: Hadronic structure and interactions

34 Nucleon matrix elements with maximally twisted fermions

We present a lattice calculation of nucleon matrix elements with twisted mass fermions. In this talk we focus on results for the moments of parton distributions. The relevant renormalization constants are carried out non-perturbatively.

Speaker: Simon Dinter (NIC, DESY Zeuthen)

Slides dinter_talk_Lattice2010.pdf

35 Baryon axial coupling constants and quark momentum fractions with Nf=2+1 dynamical fermions

In this talk we will report on recent results of the QCDSF Collaboration on investigations of baryon structure using configurations generated with Nf=2+1 dynamical flavours of O(a)-improved Wilson fermions. With the strange quark mass as an additional dynamical degree of freedom in our simulations we avoid the need for a partially quenched approximation when investigating the properties of particles containing a strange quark, e.g. the hyperons. In particular, we will focus on the nucleon and hyperon axial coupling constants and quark momentum fractions.

Speaker: Frank Winter (QCDSF Collaboration)

Slides winter.pdf

36 Transverse momentum distributions inside the nucleon from lattice QCD

Transverse momentum dependent parton distribution functions encode information about the intrinsic motion of quarks in the nucleon. We present first calculations on the lattice, based on MILC gauge configurations and propagators from LHPC. The resulting spin-dependent densities exhibit visible dipole deformations in the nucleon. For our exploratory calculations we employ a non-local operator with a non-perturbatively renormalized direct Wilson line. A more elaborate operator geometry is needed for quantitative comparisons to azimuthal asymmetries observable in experiments, such as the Sivers effect in semi-inclusive deeply inelastic scattering.

Speaker: Bernhard Musch (Jefferson Lab, USA)

Slides musch.pdf

37 Nucleon structure from RBC/UKQCD 2+1 flavor DWF dynamical ensembles at a nearly physical pion mass

We report the status of nucleon structure calculations on the 2+1 flavor domain-wall fermions ensembles with pion masses as low as 180 MeV on a lattice with about 4.5 fm spatial extent. A combination of the Iwasaki+dislocation- suppressing-determinant-ratio (I+DSDR) gauge action and DWF fermion action allows us to generate these ensembles at cutoff of about 1.4 GeV while keeping the residual mass small, and thus allows for a lattice spatial extent of 32 lattice units or about 4.5 fm.

Speaker: Shigemi Ohta (IPNS/KEK and SOKENDAI Graduate University of Advanced Studies and RBRC/BNL)

Slides ohta.pdf

38 Parton Distribution Amplitudes

We calculate the first two moments of the light-cone distribution amplitudes for the pseudoscalar mesons (pi and K) and the longitudinally polarised vector mesons (rho, K* and phi) as part of the UKQCD and RBC collaborations' N_f=2+1 domain-wall fermion phenomenology programme. These quantities were obtained with a good precision and, in particular, the expected effects of SU(3)-flavour symmetry breaking are observed. Operators are renormalised nonperturbatively and extrapolations to the physical point are made, guided by leading order chiral perturbation theory. The main results presented are for two volumes (16 and 24 cubed) with a common lattice spacing. Further to this, preliminary results for a lattice with a finer lattice spacing (32 cubed) will be discussed.

Speaker: Thomas Rae (The University of Southampton)

Slides rae.pdf

Parallel 04: Nonzero temperature and density

39 Finite temperature phase transition with two flavors of improved Wilson fermions

The critical temperature is computed and the nature of the QCD finite temperature phase is studied for N_f = 2 dynamical flavors of nonperturbatively improved Wilson fermions. The new simulations are performed on lattices 40^3 x 14 with lattice spacing and pion mass at the transition close to 0.08 fm and 200 MeV, respectively. We find the deconfinement and chiral phase transitions to coincide within numerical precision. Our results are in broad agreement with a second order phase transition in the chiral limit. The critical temperature at the physical quark mass is found to be about 170 MeV.

Speaker: Vitaly Bornyakov (Institute for High Energy Physics)

Slides 1_talk14.05.10.pdf

40 EOS in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach

Status of our study on the equation of state in 2+1 flavor QCD will be presented. We apply the T-integration method to calculate the EOS in the fixed scale approach nonperturbatively. The calculations are performed with the same parameters as the CP-PACS/JLQCD spectrum study, in which the non-perturbatively improved Wilson quarks coupled with the RG improved glue are adopted. We discuss the results in 2+1 QCD by comparing with the results in quenched QCD at fixed scale.

Speaker: Takashi Umeda (Hiroshima Univ.)

Slides 2_lattice2010umeda.pdf

41 Thermal transition temperature from twisted mass QCD

We present the current status of lattice simulations with Nf=2 maximally twisted mass fermions at finite temperature. In particular, the determination of the thermal transition temperature will be discussed.

Speaker: Lars Zeidlewicz (Uni Muenster / Uni Frankfurt)

Slides 3_zeidlewicz.pdf

42 Towards the N_{f}=2 deconfinement transition temperature with O(a) improved Wilson fermions

A lot of effort in lattice simulations over the last years has been devoted to studies of the QCD deconfinement transition. Most state-of-the-art simulations use so called rooted staggered fermions, and are also affected by systematic uncertainties, such as coarse lattices and heavy sea quarks. Therefore it is important to probe the transition with other fermion actions and improve on systematics. I report on an ongoing study of the transition, using two degenerate flavours of nonperturbatively O(a) improved Wilson fermions. We start with N_{t}=12 lattices, aiming at chiral and continuum limit with very light quarks and lattices up to N_{t}=20.

Speaker: Bastian Brandt (Institut für Kernphysik, Johannes Gutenberg-Universitaet, Mainz)

Slides 4_Vortrag.pdf

43 The Chiral Magnetic Effect and symmetry breaking in SU(3) quenched theory

We study properties of the non-Abelian vacuum in the presence of constant external magnetic field within the quenched SU(3) lattice gauge theory with tadpole-improved Wilson-Symanzik action and using the chirally invariant lattice Dirac operator. We have found that the magnetic field enhances the chiral symmetry breaking in the confinement phase as well as the local fluctuations of both electric/chiral charge and electromagnetic current in direction of the magnetic field. These fluctuations can be recognized as evidence of the Chiral Magnetic Effect (CME), which is observed by the STAR Collaboration in heavy ion collisions at RHIC. The paramagnetic polarization of the quarks’ spins in strong magnetic field has been also observed in our simulation and the chiral magnetization as a function of the field strength has been calculated using near-zero eigenmodes of overlap fermions. We also investigate the correlator of two vector currents in this theory and extract the electric conductivity of the vacuum from the spectral function, which corresponds to this correlator.

Speaker: Tigran Kalaydzhyan (DESY-Hamburg)

Slides 5_kalaydzhyan_lat.pdf

Parallel 06: Vacuum structure and confiment

44 Further investigation of massive Landau-gauge propagators in the infrared limit

We study the infrared limit of Landau gluon and ghost propagators on large lattices and investigate how the behavior according to the so-called massive solution is affected by temperature.

Speaker: Tereza Mendes (University of Sao Paulo)

Slides mendes.pdf

45 Colour fields generated by static sources of different SU(3) representations.

The colour fields, created by static sources belonging to different SU(3) representations, from the 3 to the 27, are computed in quenched SU(3) lattice QCD, in a $24^3\times 48$ lattice at $\beta=6.2$ and $a=0.07261(85)\,fm$. We utilize the technique of generalized Wilson Loops to localize the sources, correlated with plaquettes to measure the respective colour fields. We investigate the Casimir scaling of the fields, measured in the static potentials by Bali. We also study the coherence length, comparing with the dual Ginzburg-Landau approach. With the penetration and coherence lengths we determined the Ginzburg-Landau dimensionless parameter, this result is consistent with a type II superconductor picture, and with an effective dual gluon mass of $0.905\pm0.163$ GeV.

Speaker: Bicudo Pedro (Instituto Superior Técnico, Lisboa)

Slides bicudo.ppt

46 Propagators in lattice Coulomb gauge and confinement mechanisms

We review the status of lattice simulations for propagators in Coulomb gauge. In particular, we focus on renormalization issues for the static propagators and on the relation to the Gribov-Zwanziger and dual-superconductor confinement mechanisms. We also show how a vanishing static Coulomb gauge gluon propagator can agree with the lattice Landau gauge results; the IR effective gluon mass in the latter coincides with the Gribov mass. Strong coupling limits of both gauges are briefly commented upon.

Speaker: Giuseppe Burgio (Universität Tübingen)

Slides burgio.pdf

47 Hamiltonian Flow in Coulomb Gauge Yang-Mills theory

We derive a new Hamiltonian renormalisation group flow equation for Yang-Mills theory in Coulomb gauge. The flow equations for the static gluon and ghost propagators are solved numerically under the assumption of a bare ghost gluon vertex. The resulting propagators are compared with lattice data and results obtained from the Dyson-Schwinger equations following from a variational solution of the Yang-Mills Schrödinger equation.

Speaker: Hugo Reinhardt (Tübingen University)

Slides Reinhardt.pptm

48 New results on the effective string corrections to the interquark potential.

We propose a new approach to the study of the interquark poten- tial in LGTs. Instead of looking at the expectation value of Polyakov loop correlators we study the modifications induced in the chromoelectric flux due to the presence of the Polyakov loops. This approach is particularly effective in the case of abelian LGTs where, with a careful use of duality relations this study can be performed in a very efficient way. The major advantage of this numerical strategy is that it allows to eliminate the dominant effective string correction to the interquark potential (the Luscher term) thus giving an unique opportunity to test higher order terms. Performing a set of simulations in the 3d gauge Ising model we were thus able to precisely identify and measure both the quartic and the sextic effective string corrections. While the quartic term perfectly agrees with the Nambu-Goto one the sextic term is definitely different. We discuss the implications of this finding in view of the recent proof of the universality of the sextic correction by Aharony and Karzbrun.

Speaker: Michele Caselle (TO)

Slides caselle.pdf

Parallel 08: Standard model parameters and renormalization

49 One loop matching factors for staggered four-fermion operators with improved glue

We present results of one-loop perturbative matching factors for four-fermion operators constructed using HYP/$\overline{\rm FAT7}$ staggered fermions. We use both unimproved (Wilson) and improved (Symanzik) gluon actions. The latter choice of action is relevant to our ongoing project of calculating $B_K$ and $\epsilon'/\epsilon$. To estimate the quantitative effect of using Symanzik improved gluon action, we compare the following four choices of actions: (1) unimproved staggered fermions with Wilson gluons (2) HYP/$\overline{\rm FAT7}$ staggered fermions with Wilson gluons, (3) unimproved staggered fermions with Symanzik gluons, and (4) HYP/$\overline{\rm FAT7}$ staggered fermions with Symanzik gluons. We discuss the effect of the improved glue on reducing the size of one-loop perturbative corrections to four-fermion operators.

Speaker: Jongjeong Kim (Department of Physics and Astronomy, Seoul National University)

Slides jj.kim.pdf

50 Renormalization constants for one-derivative fermion operators in twisted mass QCD

We present perturbative and non-perturbative results on the renormalization constants of the twist-2 vector and axial vector operators. Non-perturbative results are obtained using the twisted mass Wilson fermion formulation employing two degenerate dynamical quarks and the tree-level Symanzik improved gluon action for pion masses in the range of about 450-260 MeV and at values of the lattice spacing 0.055, 0.07, 0.089 fm. Subtraction of O(a^2) terms is carried out by performing the perturbative evaluation of these operators at 1-loop and up to O(a^2). The renormalization conditions are defined in the RI'-MOM scheme, for both perturbative and non-perturbative results. The Z-factors, obtained for different values of the renormalization scale, are evolved perturbatively to a reference scale set by the inverse of the lattice spacing. In addition, they are translated to MS bar at 2 GeV using 3-loop perturbative results for the conversion factors.

Speaker: Martha Constantinou (University of Cyprus)

Slides M_Constantinou.pdf

51 Renormalisation of composite operators in lattice QCD: perturbative versus nonperturbative

The perturbative and nonperturbative renormalisation of quark-antiquark operators in lattice QCD with two flavours of clover fermions is investigated within the research programme of the QCDSF collaboration. Operators with up to three derivatives are considered. The nonperturbative results based on the RI-MOM scheme are compared with estimates from one- and two-loop lattice perturbation theory.

Speaker: Meinulf Göckeler (Institute for Theoretical Physics, University of Regensburg)

Slides Gockeler.pdf

52 Heavy-light current-current correlators

HPQCD Collaboration I will discuss further results from studies of current-current correlators using HISQ quarks, extending on results for hevyonium correlators to the significantly more challenging heavy-light case. The aim of this work is to determine nonperturbative Z factors for heavy-light currents.

Speaker: Jonna Koponen (University of Glasgow)

Slides Jonna_Koponen.pdf

Parallel 10: Hadron spectroscopy

53 Low-energy parameters of pion and nucleon from two-flavor lattice QCD at physical quark masses

I report on recent simulations of clover fermions with masses extending down to the physical point. The focus is on pion and nucleon two-point functions. Among the topics being addressed are the light quark masses, the low-energy constants of the underlying chiral and heavy-baryon effective theories, the nucleon sigma term, the pion decay constant, as well as effects of the finite volume.

Speaker: Gerrit Schierholz (DESY/Regensburg)

Slides schierholz.pdf

54 Mesons and baryons masses with low mode averaging

We describe and test a method known in the literature as low-mode averaging to improve Euclidean two-point functions in lattice QCD using the low-lying eigenmodes of the Wilson-Dirac operator. The contribution from the low modes is averaged over all positions of the quark sources while the contribution from high modes is estimated in the traditional way using one source point per lattice. We apply this method to different baryon and meson two point functions and we compare the improvements using either the eigenmodes of the non-hermitian Dirac operator $D$ or the eigenmodes of the hermitian operator $Q=\gamma_5 D$. The convergence strongly depends on the parity of the states.

Speaker: Luca Castagnini (University of Regensburg)

Slides castagnini.pdf

55 Highly excited and exotic meson spectroscopy from dynamical lattice QCD

I will discuss recent progress in extracting highly excited and exotic meson spectra using lattice QCD. New results in the light meson sector will be presented, where a combination of techniques and dynamical anisotropic lattices have enabled us to confidently identify the spin of extracted states. Highlights include many states with exotic quantum numbers and, for the first time in a lattice QCD calculation, spin-four states. I will conclude with comments on future prospects.

Speaker: Christopher Thomas (Jefferson Lab)

Slides thomas.pdf

56 Recent results on excited hadrons in 2-flavor QCD

We present results of meson and baryon spectroscopy using the Chirally Improved Dirac operator on lattices of size $163 \times 32$ with two mass-degenerate light sea quarks and two+one valence quarks. Several configuration ensembles with pion masses ranging from $300$ to $550$ MeV and lattice spacings close to $0.15\,$ fm are investigated. The analysis of the states is done with the variational method, allowing for determination of ground states and excitations in several channels. We discuss the possible signal of scattering states in various channels, considering masses and eigenvectors.

Speaker: Georg Philipp Engel (Institut fuer Physik, Karl-Franzens Universitaet Graz, Austria)

Slides Engel.pdf

Parallel 12: Chiral symmetry

57 Renormalization of minimally doubled fermions

Minimally doubled fermions have been proposed as a strictly local discretization of the QCD quark action, which also preserves chiral symmetry at finite cut-off. We study the renormalization and mixing properties of two particular realizations of minimally doubled fermions in lattice perturbation theory at one loop. We also construct conserved axial-vector currents, which have a simple form involving only nearest-neighbors sites.

Speaker: Stefano Capitani (University of Mainz)

Slides lat2010-capitani.pdf

58 Pairs of massless quarks on the lattice from staggered fermions

A version of overlap fermions built from staggered rather than Wilson fermions is presented. It has the remarkable property of reducing the 4 flavors (tastes) of the staggered fermion to two flavors, which can be taken as the up and down quarks in Lattice QCD. The exact flavored chiral symmetry of the staggered fermion gets converted into an unflavored Ginsparg-Wilson chiral symmetry of the new overlap fermion, which also has pairs of exact chiral zero-modes satisfying the Index Theorem. A domain wall formulation giving a truncation of this overlap construction is also obtained.

Speaker: David Adams (Nanyang Technological University)

Slides adams1-lat10.pdf

59 Numerical properties of overlap staggered fermions

David Adams has recently proposed a 2-flavor overlap Dirac operator based on the Neuberger construction, but using a staggered kernel. We illustrate how this operator satisfies the index theorem, investigate some of its promising properties, and compare with the usual Neuberger operator.

Speaker: Philippe de Forcrand (ETH Zurich & CERN)

Slides Forcrand_LAT10.pdf

60 Staggered chiral perturbation theory in the two-flavor case

In the light pseudoscalar sector, I study rooted staggered chiral perturbation theory in the two-flavor case. The pion mass and decay constant are calculated through NLO for a partially-quenched theory. In the limit where the strange quark mass is large compared to the light quark masses and the taste splittings, I show that the SU(2) staggered chiral theory emerges from the SU(3) staggered chiral theory, as expected. Explicit relations between SU(2) and SU(3)low energy constants and taste-violating parameters are given. A brief summary of updated SU(2) chiral fits to the MILC lattice data is presented.

Speaker: Xining Du (Washington University in St.Louis)

Slides Du.pdf

Other activities

Tuesday, 15 June

Parallel 13: Applications beyond QCD

61 Toward the Nearly Conformal Composite Higgs Mechanism

I will review chiral symmetry breaking and gauge coupling renormalization close to the conformal threshold in SU(3) gauge theories focussed on twelve flavors in the fundamental fermion representation and two flavors in the sextet fermion representation.

Speaker: Julius Kuti (University of California, San Diego, Department of Physics)

Slides jkLattice2010.pdf

62 Running couplings in 12 flavor QCD

QCD with 12 flavors is a candidate near-conformal gauge theory if its beta function has a near-zero with a slowly varying running coupling. We test various running coupling schemes against this hypothesis.

Speaker: Kieran Holland (University of the Pacific)

Slides hollandLattice2010.latest.pdf

63 Confining vs. conformal scenario for SU(2) with 2 adjoint fermions. Mesonic spectrum.

The Minimal Walking Technicolor model, based on the SU(2) gauge group with two Dirac adjoint fermions, is expected to lie close to the lower boundary of the conformal window. As such, it is believed to possess a dynamics different enough from QCD to be a viable candidate for a Technicolor theory. We present a detailed analysis of the mesonic spectrum of this model in which we aim to reach the chiral limit while controlling the systematic errors. Comparing our data to the expected behaviors for a QCD-like theory and for an IR conformal theory, we show that the latter scenario is favored.

Speaker: Claudio Pica (CP3-Origins, SDU)

Slides pica_lattice2010.pdf

64 Confining vs. conformal scenario for SU(2) with adjoint fermions. Gluonic observables.

Walking technicolor is a mechanism for electroweak symmetry breaking, alternative to the Higgs field. The Higgs mechanism is provided by chiral symmetry breaking in the technicolor theory. Essential ingredient is the vicinity to an IR fixed point, which could reconcile technicolor to the electroweak precision tests. SU(2) with two Dirac adjoint fermions has been proposed as a candidate for walking technicolor. Understanding whether this theory is confining or IR-conformal is a challenging problem, which can be addressed by means of numerical simulations. We have pointed out that a clean signal for the existence of an infrared fixed point in this theory can be obtained by looking for signatures in the gluonic sector. In this talk, the technical details of our calculations and possible systematic errors are discussed. Although those measurements are technically difficult, they can be kept under good control even with a limited number of configurations.

Speaker: Agostino Patella (Swansea University)

Slides patella.pdf

Parallel 15: Nonzero temperature and density

65 Charmonium spectral functions in quark-gluon plasma from lattice QCD with large spatial volume

From phenomenological considerations, J/psi suppression was proposed as a signature of QGP production in relativistic heavy ion collisions, and has been considered as one of the most promising ones. On the other hand, previous studies from lattice QCD and effective theories show possibility of existence of q-\bar{q} correlations even above the critical temperature. We study the charmonium spectral functions in quark-gluon plasma on 64^3 X Nt quenched anisotropic lattices, analyzing correlation functions of charmonium by the maximum entropy method (MEM). In particular, we focus on finite momentum effects on the charmonium spectral functions in order to understand J/Psi suppression mechanism in relativistic heavy ion collisions from the first principles of QCD.

Speaker: Chiho Nonaka (Nagoya University)

Slides 1_nonaka.pdf

66 An application of the variational analysis to calculate the meson spectral functions

We calculate the meson spectral functions (SPFs) via the variational analysis to investigate the behavior of discrete spectra on a finite volume lattice at finite temperature. Although the vairational method can not extract the whole information of the SPFs, it can calculate the value of SPFs at several low-lying spectra. Therefore, the method will be useful to test if the low-lying states dissociate above $T_c$. Moreover, we can improve the signals by increasing the number of basis operators -- besides the point source operator, we introduce several smeared operators using Gaussian smearing functions. Our simulations are carried out on a quenched anisotropic lattice using the standard plaquette gauge action and the $O(a)$-improved Wilson fermion action. We test the method by comparison with the analytic solutions in the free quark case. Furthermore we calculate the 1S, 2S, 1P and 2P charmonia SPFs at temperatures in the range $0.88T_C$ to $2.3T_C$.

Speaker: Hiroshi Ohno (University of Tsukuba)

Slides 2_lattice2010_ohno.pdf

67 Charmonium correlation and spectral functions at finite temperature

We investigate the charmonium correlators and spectral functions in quenched QCD, using Clover improved Wilson fermions on very fine (0.01 fm) isotropic lattices at 0.75 $T_c$ ($ 128^3\times96 $) and 1.5 $T_c$ ($128^3 \times48 $). We focus on the thermal modification of the correlation and spectral functions. The charmonium dissociation temperature as well as the heavy quark diffusion constant are discussed.

Speaker: Heng-Tong DING (Bielefeld University)

Slides 3_HengTong_lattice2010.pdf

68 Estimating dilepton rates and electric conductivity from vector current correlation functions in quenched QCD

We report on a continuum extrapolation of the vector current correlation function for light valence quarks in the deconfined phase of quenched QCD. The vector meson correlator is calculated at T=1.5 Tc at four values of the cut-off on lattices up to size 128^3x48. We determine the first three, non-vanishing thermal moments of the vector meson spectral function. We find that ratios of thermal moments agree with those for free, massless quarks within 1% accuracy, while the correlator at the midpoint, t=1/2T is about 8% larger than the free vector correlation function. We discuss resulting constraints on the electric conductivity and the thermal dilepton rate in a quark gluon plasma.

Speaker: Frithjof Karsch (Brookhaven National Laboratory and Bielefeld University)

Slides 4_Karsch_lat10.pdf

Parallel 17: Weak decays and matrix elements

69 Computing the long-distance contribution to second order weak amplitudes

The calculation of the long-distance contribution to the K^0-\overline{K}_0 mass matrix is divided into three parts: First, the calculation of the matrix element between kaon states of the product of two space-time integrated, $\Delta S=1$, four-quark weak operators. Second an RI/MOM subtraction to remove the short distance part of this matrix element in a fashion consistent with the calculation of the physical short distance part. Third an application of the Lellouch-Luscher method, generalized to second order in the weak interactions, to control finite volume errors. Such an approach promises to permit accurate lattice calculation of the $K_L$-$K_S$ mass difference and the long-distance contributions to $\epsilon_K$.

Speaker: Norman Christ (Columbia University)

Slides Christ.pdf

70 Preliminary study of the non-perturbative renormalization of K-> pi (pi) operators, with Nf=2+1 Domain Wall fermions

At the leading order of the OPE, they are ten 4-quark operators which contribute to the \Delta S=1 effective Hamiltonian. The mixing pattern of these operators under renormalization is governed by their chiral properties. Thus it is crucial to perform this computation with fermions which preserve (or almost preserve) chiral symmetry, such as Domain Wall fermions. We present here our strategy to compute the relevant renormalization matrix following the Rome-Southampton method, with point and volume sources. In particular we will show how we can deal with the potentially dangerous eye contractions.

Speaker: Nicolas Garron (University of Edinburgh)

Slides garron.pdf

71 $\Delta I = 3/2$, $K \to \pi \pi$ Matrix Elements with Nearly Physical Pion Masses

$\Delta I = 3/2$ channel $K\to\pi\pi$ matrix elements are calculated with a variety of kaon masses, pion masses, and pion momenta on quenched $24^3\times 64$, $L_s=16$ lattices using the DBW2 action and domain wall fermions. After an interpolation in pion momentum to energy conserving kinematics is performed, the dependence of the matrix elements on $m_\pi$ and $m_K$ is studied. The lightest pion mass in the study is 165 MeV, corresponding to $m_\pi L\approx 3$. Preliminary results are also presented from a calculation on RBC/UKQCD $32^3\times 64$, $L_s=32$ lattices with 2+1 flavors of dynamical quarks using the Iwasaki+DSDR gauge action and domain wall fermions. This second calculation is done with a single pion mass ($m_\pi=146\text{ MeV}$, partially quenched) and kaon mass that are nearly physical, and with nearly energy conserving kinematics. The two calculations are compared with each other and with experiment, and the systematic errors are estimated.

Speaker: Matthew Lightman (Columbia University)

Slides lightman.pdf

72 Preliminary results of $\Delta I=1/2$ and $3/2$, $K$ to $\pi\pi$ Decay Amplitudes from Lattice QCD

We report a direct lattice calculation of the $K$ to $\pi\pi$ decay matrix elements for both $\Delta I=1/2$ and $3/2$ channels on 2+1 flavor, domain wall fermion, $16^3\times32$ lattices. All possible contractions are carefully listed and calculated and identities among them are verified. The decay into the isospin zero $\pi\pi$ final state, which receives contributions from the disconnected graphs, is very difficult to calculate, but a clear signal in the similar disconnected $\pi\pi$ correlator can be seen. We also demonstrate that a large explicit subtraction of the divergent $\bar{s}\gamma_5d$ contribution is necessary even for the case of kinematics which are nominally energy conserving. Preliminary results, some with large errors, will be presented for the various contributions to the renormalized weak matrix elements $A_0$ and $A_2$ for the $m_\pi=420MeV$ and $m_\pi=236MeV$(partially quenched light quark) cases.

Speaker: Qi Liu (Columbia University)

Slides liu.pdf

73 Matrix element of the electromagnetic operator between kaon and pion states

We investigate the calculation of the matrix element of the electromagnetic operator between kaon and pion states, using maximally twisted-mass fermions with two flavors of dynamical quarks. The operator is renormalized non-perturbatively and our simulations at different values of the lattice spacing and pion masses are extrapolated to the continuum limit and to the physical kaon and pion masses.

Speaker: Itzhak Baum (Rome University "La Sapienza")

Slides Baum.pdf

Parallel 19: Standard model parameters and renormalization

74 Hunting the static energy renormalon

We present new results from lattice perturbation theory (LPT) for the the static quark self-energy (SE) obtained from Polyakov loops at high orders (up to 12 loops). For the first time we implemented Numerical Stochastic Perturbation Theory (NSPT) with twisted boundary conditions (TBC), thereby eliminating zero modes. In previous simulations at high beta, TBC were shown to dramatically reduce the finite-volume corrections on perturbative expansions [e.g. Nobes et al., Nucl. Phys. Proc. Suppl., 2002, 106, 838-840]. We exploit this for measuring Polyakov loops up to 12 loops. From this one can extract the SE. Renormalon physics predicts the SE to exhibit a leading renormalon which differs significantly from its far more studied Plaquette counterpart: firstly, the SE's factorial divergence is expected to have a different asymptotic behaviour. Secondly, the leading SE renormalon should emerge four times as fast in the perturbative expansion, due to its position in the Borel plane. We will confront these predictions with our simulations. We will also present results for the SE in the octet representation.

Speaker: Clemens Bauer (University of Regensburg, Germany)

Slides bauer.pdf

75 Scale r0 and the static potential from the CLS lattices

We report on the measurement of the static potential and the scale r0 from HYP-smeared Wilson loops in two flavour QCD. We analyse the quark mass dependence of the potential and r0 at two lattice spacings. The high statistics at one of the parameter combinations allows for an estimate of the influence of slow Monte Carlo modes on the the statistical errors. We also compare the QCD static potential around distance r0 with the static potential obtained from effective bosonic string theory.

Speaker: Björn Leder (Bergische Universitaet Wuppertal)

Slides leder.pdf

76 Current Status of Improved Fermilab Fermions

Recently, the Fermilab heavy quark action was extended to include dimension six and seven operators in order to reduce the discretization errors. In this talk, we present results of the first numerical simulations with this action where we study the masses of the quarkonium and heavy-light systems and monitor the discretization errors.

Speaker: Mehmet Oktay (The University of Utah)

Slides oktay.pdf

77 Computing the B*Bpi coupling with relativistic heavy quarks and domain wall fermions

The effective coupling constant $g_{VP\pi}$, describing the coupling of heavy mesons to the pseudoscalar Goldstone bosons (pions), is one of the fundamental parameters of the effective chiral lagrangian for heavy mesons. This coupling encodes non-perturbative QCD effects describing the decay of heavy vector particles into pseudoscalars, $V\to P\pi$. Beside its direct physical relevance in the D system it is also of phenomenological importance to estimate this coupling non-perturbatively in the B system. I report on the (first) ongoing computation of $g_{VP\pi}$ using the non-perturbatively tuned relativistic heavy quark action (RHQ) to treat the c- and b-quark. We use domain wall light fermions and work on dynamical 2+1 DWF configurations as produced by the RBC/UKQCD collaboration.

Speaker: Patrick Fritzsch (School of Physics & Astronomy, University of Southampton)

Slides fritzsch.pdf

Parallel 21: Hadron spectroscopy

78 Glueballs in the radiative J/psi decays

In the quenched approximation, glueball-vector-current-Jpsi three point functions are calculated on an anisotropic lattice with very high statistics. Using the relevant form factors derived from these three point functions, we also give a prediction of the radiative decay widths of J/psi to scalar and pseudoscalar glueballs.

Speaker: Ying Chen (Institute of High Energy Physics, Chinese Academy of Sciences, China)

Slides chen.pdf

79 Rho decay from twisted mass fermions

We calculate the P-wave pion-pion scattering phase in the rho decay channel using two flavors of maximally twisted mass fermions at pion masses ranging from 290 MeV to 480 MeV and lattice spacings of 0.079 fm and 0.063 fm. Making use of finite-size methods, we evaluate the pion-pion scattering phase in the center-of-mass frame and two moving frames. Using all three frames, we find a good description of the scattering phase as a function of the energy in the resonance region. From this we extract the rho mass and decay width and study its quark mass dependence.

Speaker: Xu Feng (NIC, DESY)

Slides feng.pdf

80 Calculatin of $\rho$ meson decay width from the PACS-CS configurations

We present our results of the $\rho$ meson decay width estimated from the scattering phase shift for $I=1$ two pion system. Calculations are carried out with $N_f=2+1$ gauge configurations previously generated by the PACS-CS Collaboration with the Iwasaki gauge action and nonperturbatively $O(a)$-improved Wilson fermion at $m_\pi/m_\rho=0.46$ on $32\times 64$ ($La=2.9 fm$). The finite size method presented by Rummukainen and Gottlieb is employed to evaluated the scattering phase shift from energy eigenvalues.

Speaker: Naruhito Ishizuka (University of Tsukuba)

Slides ishizuka.pdf

81 Extracting resonance parameters from lattice data (Part I)

Monte Carlo simulations of the 4d O(4) model in the broken phase are performed to determine the parameters of a resonance. We discuss the applicability of a method, based on the probability distribution concept, useful in the realistic case of a large width resonance. The application to study the QCD hadron spectrum is discussed.

Speaker: Pietro Giudice (Trinity College Dublin)

Slides giudice.pdf

82 Extracting resonance parameters from lattice data: Part II

The standard method for extracting resonance parameters on the lattice is through Luscher's formula. We study the application of this formula to the 4d O(4) sigma model and contrast it with the recently proposed probability distribution method. Connections to resonances in QCD are discussed.

Speaker: Darrán McManus (Trinity College, Dublin, Ireland)

Slides mcmanus.pdf

Parallel 23: Chiral symmetry

83 Magnetic-Field-Induced insulator-conductor transition in quenched lattice gauge theory

We study the correlator of two vector currents in quenched lattice gauge theory with chirally invariant lattice Dirac operator with constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of magnetic field, while for other components the correlation length slightly decreases. We apply the Maximal Entropy Method to extract the spectral function which corresponds to this correlator. The value of this spectral function in the limit of zero frequency yields, by virtue of the Green-Kubo relations, the electric conductivity of quenched lattice gauge theory. In the confinement phase the magnetic field induces nonzero electric conductivity, but only in the direction of the field. In the deconfinement phase the conductivity practically does not depend on the magnetic field.

Speaker: Pavel Buividovich (ITEP (Moscow, Russia) and JINR (Dubna, Russia))

Slides CME_for_FRRC.pdf

84 QCD Rotator with Light Quarks up to NNL Order

We consider 2-flavour QCD with light quark masses in a small spatial box, where the low lying excitations are that of an $O(4)$ rotator. This problem can be treated in chiral perturbation theory ($\delta$-regime). Up to NNL order the final result depends only on a few low energy constants $F$, $\Lambda_1$, $\Lambda_2$ and $B$. Comparing these results with that of numerical simulations in QCD should help to measure these low energy constants to good precision.

Speaker: Manuel Weingart (Institute for Theoretical Physics, University of Bern)

Slides weingart.pdf

85 Brillouin improvement for Wilson fermions

We present a Wilson type operator obtained by including terms in both the Laplacian as well as the first-derivative stencil, such that the resulting operator remains within a hypercube. Motivated by the effect this improvement has on the eigenvalue spectrum, we investigate the approach to the continuum limit of several physical quantities. Throughout we compare to the standard Wilson operator.

Speaker: Giannis Koutsou (University of Wuppertal and Juelich Supercomputing Center)

Slides koutsou.pdf

86 Low-energy constants from Dirac eigenvalue correlators at NNLO in the epsilon expansion

We calculate the next-to-next-to-leading order (NNLO) contributions in the epsilon expansion with a small imaginary chemical potential and discuss their relevance to Dirac eigenvalue correlators. We show how to minimize systematic deviations from random-matrix theory by an optimal choice of lattice geometry in the case of two light quark flavors. Finally, we determine the low-energy constants Sigma and F from configurations of JLQCD with two dynamical overlap fermions.

Speaker: Christoph Lehner (RIKEN/BNL Research Center, Brookhaven National Laboratory, Upton, NY-11973, USA)

Slides lehner.pdf

10:10 Coffee break

Parallel 14: Applications beyond QCD

87 New results with colour-sextet quarks

We have been studying lattice QCD with colour-sextet staggered quarks, as a model for conformal/walking technicolor. We are studying the thermodynamics of these theories and using the positions of the deconfinement and chiral transitions to try to distinguish between conformal and walking behaviour. Our preliminary simulations with N_f=2, on N_t=4 and N_t=6 lattices, favoured the walking scenario. I will present new results at N_t=8. In addition I will present the results from simulations with N_f=3.

Speaker: Donald Sinclair (Argonne National Laboratory)

Slides sinclair_sardinia.pdf

88 PERTURBATIVE IMPROVEMENT OF SU(2) GAUGE THEORY WITH TWO WILSON FERMIONS IN ADJOINT REPRESENTATION

Recently there has been lot of interest in quantum field theories whose renormalization group evolution is governed by an infrared stable fixed point. This is motivated by phenomenological applications in unparticles and walking technicolor. As a continuation of an initial lattice studies of the two-color gauge theory with two adjoint Dirac flavors, we have carried out perturbative O(a) improvement with Wilson fermions. I will discuss the phenomenological motivations for this study and some technical issues.

Speaker: Tuomas Karavirta (University of Jyväskylä)

Slides Tuomas_Karavirta_Lattice2010.pdf

89 Lattice QCD with 8 and 12 Degenerate Quark Flavors

We summarize our study of QCD with 8 and 12 flavors of degenerate quarks at zero temperature, using the DBW2 gauge action and naive staggered fermions, along with the rational hybrid Monte Carlo algorithm. From measurements of hadron masses, decay constants and other low energy observables, we conclude that such a system with 8 and 12 flavors breaks chiral symmetry and exhibits confinement, although for 12 flavors we see a rapid evolution from strong to weak coupling in hadronic observables, which makes further simulations on large volumes desirable. We report on preliminary results from further simulations of the same systems at finite temperatures, to address the existence of the finite temperature phase transition and to probe the nature of such phase transition at large number of quark flavors.

Speaker: Xiao-Yong Jin (Columbia University)

Slides Jin.pdf

90 Search for the IR fixed point in the Twisted Polyakov Loop scheme (II)

We present our updated study of the nonperturbative running coupling constant in Twisted Polyakov Loop (TPL) scheme. We study the larger lattice size and the lower $\beta$ region ($\beta \geq 4.5$) in the case of SU(3) Nf=12. We discuss in detail the step scaling function, the running coupling constant, and the nonperturbative beta function using these updated data. We also discuss the comparison with the perturbative two-loop results.

Speaker: Etsuko Itou (Osaka University)

Slides itou_Lattice2010.pdf

91 Sextet QCD: slow running and the mass anomalous dimension

I report the results of Schrodinger functional calculations in the SU(3) gauge theory with two flavors of color sextet fermions, defined with the Wilson-clover action using nHYP fat links. While we cannot confirm the infrared fixed point seen with thin links, we find very slow evolution of the coupling constant, so slow that extraction of the mass anomalous dimension is straightforward.

Speaker: Benjamin Svetitsky (Tel Aviv University)

Slides Svetitsky.pdf

Parallel 16: Nonzero temperature and density

92 Renormalized Polyakov loop in the Fixed Scale Approach

I compute the deconfinement order parameter for the SU(2) lattice gauge theory, the Polyakov loop, using the fixed scale approach for several different scales and show how one can obtain a physical, renormalized, order parameter. The generalization to other gauge theories, including quenched or full QCD, is straightforward.

Speaker: Rajiv V. Gavai (Tata Institute, Mumbai)

Slides 1_gavai.pdf

93 Deconfinement transition in QCD near the heavy quark limit

We study the order of the deconfinement phase transition in QCD with Wilson quarks near the heavy quark limit. We identify the transition from the shape of an effective potential computed from the histogram of the plaquette. We find that the first order transition of the heavy quark limit gets weaker as the quark mass decreses and turns into a crossover at a finite quark mass. We estimate the end point $\kappa_{\rm ep}$ of the first order phase transition.

Speaker: Hana Saito (University of Tsukuba)

Slides saito_1006_Lattice2010.pdf

94 Effective Polyakov-loop theory for pure Yang-Mills from strong coupling expansion: analytical details

Lattice Yang-Mills theories at finite temperature can be mapped onto effective 3D Spin systems, thus facilitating their numerical investigation. Using strong coupling expansions we derive the effective action for Polyakov loops and investigate the effect of higher order corrections. Results and numerical details are discussed in the subsequent talk of Dr. Lottini.

Speaker: Jens Langelage (University of Bielefeld)

Slides 3_lat2010_langelage_2.pdf

95 Effective Polyakov-loop theory for pure Yang-Mills from strong coupling expansion: numerical aspects and conclusions

Within the Polyakov-loop effective theory for pure Yang-Mills obtained from a strong coupling expansion (as presented in Dr. Langelage's talk), a single simulation on a 3D system yields, in principle, a whole array of critical couplings for the full theory, at all values of $N_\tau$. Here we present the Monte Carlo details and the practical aspects of such approach, its results, and we discuss possible further improvements and extensions of the model.

Speaker: Stefano Lottini (Goethe-Universitaet, Frankfurt am Main)

Slides 4_Lottini.pdf

96 Finite temperature QCD at fixed Q with overlap fermions

We present preliminary results of the recently started project of Finite Temperature QCD with overlap fermions al KEK. We started a series of simulations to assess the effects of fixing the topological sector and we will show the first calculations of thermodynamical observables and topological susceptibility.

Speaker: Guido Cossu (KEK Theory Center)

Slides CossuLattice2010.pdf

97 N_f = 3 critical point from canonical ensemble

Results on locating the critical point for QCD at N_f =3 with the canonical ensemble approach will be presented. An algorithm aimed at simulations on larger volumes will be discussed.

Speaker: Keh-Fei Liu (University of Kentucky)

Slides Liu-lattice2010.pdf

Parallel 18: Weak decays and matrix elements

98 The B*Bpi coupling

We study an efficient method for the lattice calculation of the B*Bpi-coupling in the static limit, a parameter of the heavy meson chiral Lagrangian, paying particular attention to excited state contamination. Precise studies of the continuum limit in the quenched approximation and of the chiral behaviour with 2 flavours of improved Wilson quarks (using CLS lattices) for pion masses down to around 250 MeV are presented.

Speaker: Michael Donnellan (NIC, DESY Zeuthen)

Slides donnellan.pdf

99 Masses and Decay Constants from Relativistic Highly Improved Staggered Quarks in Full Lattice QCD

I'll give an update on the status of HPQCD's heavy hisq programme. We use a highly improved, relativistic staggered quark action to calculate masses, mass splittings and decay constants for B_s, B_c and heavyonium states.

Speaker: Eduardo Follana (Universidad de Zaragoza)

Slides follana.pdf

100 D and B Leptonic Decay Constants from Lattice QCD

We present summary results for the leptonic decay constants $f_{D}$, $f_{D_s}$, $f_B$ and $f_{B_s}$ from the now concluded initial phase of the Fermilab and MILC Collaboration's program in flavor physics. The decay constants are computed on the MILC collaboration's $2+1$ flavor Asqtad gauge ensembles. We use clover heavy quarks in the Fermilab interpretation and Asqtad improved staggered light quarks. The simultaneous chiral and continuum extrapolation is based upon partially quenched lattice results at multiple lattice spacings: $a\approx0.09$, $0.125$ and $0.15$ fm. We discuss in detail the present uncertainties and address how they will be reduced in the future.

Speaker: James Simone (Fermilab)

Slides simone.pdf

101 B meson spectrum and decay constant from Nf=2 simulations

We report about a preliminary extraction of masses and decay constants of the lowest pseudoscalar B meson states from lattice simulations with Nf=2 Wilson-Clover dynamical quarks, using a procedure recently presented by the ALPHA Collaboration. The heavy quark is described by Heavy Quark Effective Theory developed up to 1/m_b. Coefficients of the effective theory have been determined non perturbatively by matching few observables with their QCD counterpart in the Schrödinger Functional framework. Hadronic matrix elements are obtained by solving a Generalised Eigenvalue Problem on a matrix of 2-pts correlators that have been computed on CLS ensembles. We have considered several lattice spacings and sea quark masses to deal with cut-off effects and chiral extrapolation.

Speaker: Benoit Blossier (CNRS/LPT Orsay)

Slides blossier.pdf

102 HQET parameters at the 1/m order with nf=2 flavors of dynamical quarks

We present our computation of the HQET Lagrangian parameters and those of the time component of the heavy-light axial current, including 1/m corrections. They are obtained by matching non-perturbatively (in a small volume) HQET to QCD, with nf=2 flavors of dynamical quarks, and with quark masses going from the charm to beauty. These parameters can be used to compute the b-quark mass and the heavy-light decay constant in HQET including 1/m corrections.

Speaker: Nicolas Garron (University of Edinburgh)

Slides garron.pdf

103 The continuum limit of 2+1 flavor DWF ensembles

We present light pseudoscalar physics in the continuum limit of 2+1 flavour domain wall QCD by the RBC and UKQCD collaborations. We make use of a fermion action with good chiral symmetry and use two different lattice spacings. We use a new approach to match ensembles within the range of simulated masses, and apply a simultaneous chiral and continuum extrapolation. We present continuum results for pion and kaon decay constants, f_K/f_pi, quark masses and the neutral kaon mixing parameter B_K. We discuss the systematic errors arising from the choices in the analysis.

Speaker: Christopher Kelly (University of Edinburgh)

Slides kelly.pdf

Parallel 20: Standard model parameters and renormalization

104 scaling study of the non-perturbative renormalized quenched quark mass

I will present a scaling study of quenched quark masses obtained with a HEX-smeared improved Clover action. Renormalization is done in the RI-MOM scheme. I'm going to discuss specifics of the renormalization procedure and the continuum limit.

Speaker: Thorsten Kurth (Bergische Universität Wuppertal)

Slides 1_hex_scaling.pdf

105 Light, strange and charm quark masses from Lattice QCD

The ETM collaboration has recently performed a determination of light, strange and charm quark masses. The calculation has been performed using the twisted mass fermionic action at maximal twist, which is automatically O(a) improved, with two degenerate sea quarks. Four different lattice spacing and various volumes and quark masses have been analyzed. In the talk I will review the values obtained for these quantities and the method used to perform the analysis.

Speaker: Francesco Sanfilippo (Dipartimento di Fisica, universita' "La Sapienza" di Roma)

Slides 2_presentazione_villasimius.pdf

106 Charm current-current correlators in Twisted Mass lattice QCD

The strong coupling constant and the charm quark mass are two fundamental parameters of the Standard Model. The precision of their determination has been continuously improved in the past using both perturbative and non-perturbative methods and most recently combinations thereof. I report on a partially quenched investigation of charm current-current correlators using two flavours of dynamical twisted mass fermions. By matching non-perturbative results for moments of (pseudo-)scalar and (axial-)vector current correlators to continuum perturbation theory the strong coupling and the charm quark mass are extracted.

Speaker: Marcus Petschlies (Humboldt-Universitaet zu Berlin)

Slides 3_petschlies.pdf

107 Direct lattice calculation of m_d - m_u

In this work, we report on the first direct lattice calculation of the strong isospin breaking parameter, m_d - m_u. To determine this standard model parameter, we compute the hadron spectrum for several values the lattice volume, the pion mass and the strong isospin breaking parameter, and then extrapolate these results to the known experimental spectrum. We must address various systematics, the most important of which is the hadron electromagnetic self energy, which we discuss in some detail.

Speaker: Andre' Walker-Loud (Department of Physics, College of William and Mary)

Slides 4_WalkerLoud_LATT2010.pdf

Parallel 22: Hadron spectroscopy

108 Low lying baryon spectrum with Nf=2+1+1 dynamical twisted quarks.

We present first results on the octet and decuplet strange baryon spectrum with N_f=2+1+1 twisted mass quarks using a mixed action approach. Namely, we use an Osterwalder Seiler valence strange quark with a mass matched to the kaon mass computed with the unitary action. We also present results in the unitary setup, and compare with those obtained in the mixed action. This comparison is used to quantify the lattice artefacts introduced by the mixed action approach. We investigate the effect of the strange and charm quark in the sea by using two lattice spacings and comparing with our N_f=2 results [1]. [1] ETMC, Phys. Rev. D 80 114503, 2009

Speaker: Vincent Drach (LPSC)

Slides drach.pdf

109 Excited states of the nucleon in 2+1 flavour QCD

Recent developments on the determination of the spin-1/2 spectrum of the nucleon in full QCD are presented. Our focus is on the PACS-CS 2+1 flavour configurations made available through the ILDG. Using correlation matrix techniques, in which a wide variety of gauge-invariant Gaussian-smeared fermion-propagator sources and sinks are considered, excited states are determined. We consider several correlation matrices of various sizes, each constructed with a different set of basis interpolators, in order to demonstrate the invariance of the eigenstates on the basis choice. Of particular interest is the approach to the elusive Roper resonance and the nature of the level crossing between the lowest-lying even- and odd-parity eigenstates as the quark masses approach their physical values. We report new results in full QCD which differ significantly from that observed in the quenched approximation, providing further insight into QCD dynamics.

Speaker: Derek Leinweber (University of Adelaide)

Slides Leinweber.pdf

110 Nucleon, Delta and Omega excited state spectra at three pion mass values

The energies of excited states of the Nucleon, Delta and Omega baryons are calculated for Nf = 2+1 QCD using a 16^3x128 lattice. The calculations are performed for three values of the light quark mass with the strange quark mass fixed at its physical value. The corresponding values of pion mass are: 392(4), 438(3) and 521(3) MeV. For each baryon, six states are obtained in each of the 6 irreps of the double-covered octahedral group using the variational method. Spectra are compared with the experimental baryon resonance spectra. The patterns of excited states are in reasonable agreement.

Speaker: Stephen Wallace (Univ. of Maryland)

Slides Wallace.pdf

111 From strange to charmed baryons using Nf=2 twisted mass QCD.

We consider the mass spectrum for strange and charmed baryons in the partially quenched approach using the Nf=2 twisted mass configurations. The strange and the charmed octet and decuplet are computed, as well as some strange-charmed baryons. Several issues are investigated : the tuning of the strange and charm quark mass; the study of lattice artifacts using three values of the lattice spacing as small as 0.05 fm ; the dependence of baryon masses on the heavy quark mass.

Speaker: Mauro Papinutto (LPSC Grenoble)

Slides papinutto.pdf

112 Construction and Analysis of Two Baryon Correlation functions

The signal to noise ratio of baryon two point functions grows exponentially with Euclidean time hindering reliable extraction of the energy levels of the system. The problem becomes more acute in the case of two or more baryon correlation functions. For this reason special care is needed in both constructing, and analyzing two point functions of multi-baryon systems. In this talk I will discuss various approaches for constructing two point functions for two baryon systems as well as new methods for extracting the energy levels associated with these correlation functions.

Speaker: Kostas Orginos (College of William and Mary / JLab)

Slides orginos.pdf

113 Meson spectra from overlap fermion on domain wall gauge configurations

We report meson spectra obtained by using valence overlap fermion propagators generated on a background of 2+1 flavor domain wall fermion gauge configurations on the $16^3 \times 32$, $24^3 \times 64$ and $32^3 \times 64$ lattices. We use many-to-all correlators with $Z_3$ grid source and low eigenmode substitution which is more efficient in reducing errors for the hadron correlators. Three different sea quark masses along with various valence quark masses, from very low to charm mass region, are utilized for this calculation.

Speaker: Nilmani Mathur (Tata Institute of Fundamental Research, India)

Slides mathur.ppt

Parallel 24: Chiral symmetry

114 Results for light pseudoscalar mesons

We present results from the MILC collaboration's analysis of the light pseudoscalar meson sector. All of our asqtad staggered ensembles with 2+1 dynamical quark flavors have now been completed and analyzed, including lattice spacings down to 0.045 fm, and light quark masses down to 0.05 times the strange mass. We compare the results from SU(3) and SU(2) chiral perturbation theory; both sets of fits include the continuum NNLO chiral logarithms. We obtain results for decay constants, quark masses, NLO and NNLO low energy constants, and the condensates in the two- and three-flavor chiral limits.

Speaker: Claude Bernard (Washington University)

Slides bernard.pdf

115 Let's go dynamic -- a quick tour through 2+1 lattice simulations to understand chiral symmetry breaking

Several lattice collaboration performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with conventional NNLO expressions from N_f=3 Chiral Perturbation Theory, even for quantities as simple as pseudoscalar masses and decay constants. At the same time, they have obtained rather small values of the quark condensate and/or the decay constant in the N_f=3 chiral limit, which implies that N_f=3 chiral expansions are not necessarily saturated by their leading-order term. In this case, one needs to reorder the chiral expansion to analyse N_f=2+1 lattice data correctly. We will present the basic elements of such reordering in the case of pseudoscalar masses and decay constants, as well as Kl3 form factors. Fitting recent results from several lattice collaborations, we will describe the emerging picture for the pattern of chiral symmetry breaking, as well as the consequences for quantities of phenomenological interest such as f_K/f_pi and f_+(0).

Speaker: Sebastien Descotes-Genon (LPT (CNRS/Univ. Paris-Sud 11))

Slides descotes.pdf

116 Analysis of the $N_f=2+1$ lattice QCD results on the lowest-lying baryon masses using covariant ChPT

We present an analysis of the baryon-octet and -decuplet masses using covariant SU(3)-flavor chiral perturbation theory up to next-to-leading order. Besides the description of the physical masses we address the problem of the lattice QCD extrapolation. More precisely, we study the $N_f=2+1$ results recently provided by the PACS-CS, LHPC and HSC collaborations. We show that a good description of the lattice points can be achieved at next-to-leading order with the covariant loop amplitudes and phenomenologically determined values for the meson-baryon couplings. Furthermore, the extrapolations to the physical point of the results are found to be better than the linear ones given at leading-order by the Gell-Mann-Okubo approach. The importance that a reliable combination of lattice QCD and chiral perturbation theory may have for the determination of the LECs in the baryonic sector is emphasized with the prediction of the pion-baryon and strange-baryon sigma terms.

Speaker: Jorge Martin Camalich (IFIC-Valencia)

Slides camalic.pdf

117 Axial and Electromagnetic observables of hyperons in 2-flavor chiral perturbation theory

Using two-flavor chiral perturbation theories for hyperons, we study the chiral corrections to the axial charges as well as the electromagnetic properties of spin-1/2 hyperons. We first demonstrate that the virtual kaon loop contributions are well described in the two-flavor theories by terms analytic in the pion mass squared. We further show for the case of experimentally known hyperon magnetic moments and charge radii, the chiral corrections are under reasonable control, in contrast to the behavior of these observables in the three-flavor chiral expansion. Finally using lattice data and phenomenological inputs, we verify that the convergence of chiral perturbation theory is improving with increasing strangeness quantum number. The formulae we derive are ideal for performing the pion mass extrapolation of lattice QCD data obtained at the physical strange quark mass.

Speaker: Fu-Jiun Jiang (CTP, MIT)

Slides jiang.pdf

118 Progress in Electromagnetic Corrections to Staggered Chiral Perturbation Theory

To reduce errors in light-quark mass determinations from the lattice, it is now necessary to consider electromagnetic contributions to light-meson masses. Calculations with quenched photons are currently underway, and suitably-extended chiral perturbation theory is necessary to extrapolate the lattice data to the physical limit. We discuss issues of including electromagnetism on the lattice from a chiral perturbation theory perspective. We also report on the development of staggered chiral perturbation theory to be used with recent quenched-photon simulations by the MILC collaboration.

Speaker: Elizabeth Freeland (Washington University in St. Louis)

Slides freeland.pdf

119 Topological charge in two flavors QCD with optimal domain-wall fermion

We determine the topological charge and its fluctuations for the gauge configurations generated by lattice simulations of 2 flavors QCD with optimal domain-wall fermion, on a $ 16^3 \times 32 \times 16 $ lattice with Wilson gauge action at $ \beta = 5.90 $. We project the low-lying modes of the lattice Dirac operator with the Lanczos thick-restart algorithm, and obtain the topological charge, the topological susceptibility ($\chi_t$) and the second normalized cumulant ($c_4$). Our preliminary results of $\chi_t$ and $c_4$ agree with the sea-quark mass dependence predicted by the chiral perturbation theory.

Speaker: Tung-Han Hsieh (Research Center for Applied Sciences, Academia Sinica)

Slides hsieh.pdf

12:30 Lunch

Parallel 25: Hadronic structure and interactions

120 Light meson form factors in $N_f=2+1$ QCD with dynamical overlap quarks

We report on our study of pion and kaon form factors in three-flavor QCD with dynamical overlap quarks. Connected and disconnected meson three-point functions are calculated using the all-to-all propagator on a $16^3 \times 48$ lattice at a lattice spacing of 0.11 fm. We present preliminary results for the electromagnetic, scalar and weak decay form factors.

Speaker: Takashi Kaneko (KEK)

Slides kaneko.pdf

121 Wilson fermions at fine lattice spacings: scale setting, pion form factors and (g-2)

We present an update on our on-going project to compute hadronic observables for Nf=2 flacours of O(a) improved Wilson fermions at small lattice spacings. The procedure to determine the lattice scale via the mass of the Omega baryon is described. Furthermore we present preliminary results for the pion form factor computed using twisted boundary conditions, as well as for the contribution of hadronic vacuum polarisation to the anomalous magnetic moment of the muon.

Speaker: Hartmut Wittig (University of Mainz)

Slides wittig.pdf

122 Nucleon magnetic moments and electric polarizabilities

Electromagnetic properties of the nucleon are explored with lattice QCD using a novel technique. Focusing on background electric fields, we show how the electric polarizability can be extracted from nucleon correlation functions. A crucial step concerns addressing contributions from the magnetic moment, which affects the relativistic propagation of nucleons in electric fields. By properly handing these contributions, we can determine both magnetic moments and electric polarizabilities. Lattice results from anisotropic clover lattices are presented. Our method is not limited to the neutron, and we show results for the proton as well.

Speaker: Brian Tiburzi (University of Maryland)

Slides tiburzi.pdf

123 Hadron electric polarizability -- finite volume corrections

Hadron polarizability are usually measured on the lattice using the background field method. To create a uniform field one can use either periodic boundary conditions that force the electromagnetic field to assume quantized values or Dirichlet boundary conditions where the field can assume any value but the translational invariance is broken. In both cases, the energy shifts measured have finite volume corrections that decay slowly with increasing lattice size. In this talk we discuss these corrections and present results for electric polarizability on different lattice sizes.

Speaker: Andrei Alexandru (The George Washington University)

Slides alexandru.pdf

124 Magnetic Moments of Negative-Parity Baryons from Lattice QCD

We compute the magnetic moments of negative-parity baryons in the background field method. They are extracted from small mass shifts caused by external magnetic fields introduced on the lattice. The calculations are done on quenched configurations using standard Wilson actions, with pion masses down to about 500 MeV, several field strengths, and high statistics. For comparison purposes, we also extract the magnetic moments of their positive-parity counterparts.

Speaker: Frank Lee (George Washington University)

Slides lee.pdf

Parallel 27: Nonzero temperature and density

125 Constraints on the QCD phase diagram at imaginary mu

We present unambiguous evidence from lattice simulations of QCD with three degenerate quark species for two tricritical points in the $(T,m)$ phase diagramat fixed imaginary $\mu/T=i\pi/3$ mod $2\pi/3$, one in the light and one in the heavy mass regime. They represent the boundaries of the chiral and deconfinement critical lines continued to imaginary chemical potential, respectively. It is demonstrated that the shape of the deconfinement critical line for real chemical potentials is dictated by tricritical scaling and implies the weakening of the deconfinementtransition with real chemical potential. The generalization to non-degenerate and light quark masses is discussed.

Speaker: Owe Philipsen (University of Frankfurt)

Slides philipsen.pdf

126 Curvature of the QCD phase transition line in a finite volume

The curvature which characterizes the QCD phase transition at finite temperature and small values of the chemical potential is accessible to lattice simulations. The results for this quantity which have been obtained by several different lattice simulation methods differ due to different numbers of flavors, different pion masses and different sizes of the simulations volumes. In order to reconcile these results, it is important to investigate finite-volume effects on the curvature. We investigate the curvature of the chiral phase transition line at finite temperature and chemical potential in a finite volume. We use a phenomenological model for chiral symmetry breaking and apply non-perturbative Renormalization Group methods which account for critical long-range fluctuations at the phase transition. We find that there is an intermediate volume region in which the curvature of the phase transition line is actually reduced relative to its infinite-volume value, provided periodic spatial boundary conditions are chosen for the quark fields. Size and position of this region depend on the value of the pion mass. Such an effect could account for differences in the curvature between lattice simulations in differently sized volumes. We discuss implications of our results for the QCD phase diagram.

Speaker: Bertram Klein (Physik Department, Technische Universität München)

Slides klein.pdf

127 The critical line of QCD with four degenerate quarks

We determine the pseudo-critical couplings at imaginary chemical potentials by high-statistics Monte Carlo simulations of QCD with four degenerate quarks at non-zero temperature and baryon density by the method of analytic continuationan. We reveal deviations from the simple quadratic dependence on the chemical potential visible in earlier works on the same subject. Finally, we discuss the implications of our findings for the shape of the pseudo-critical line at real chemical potential, comparing different possible extrapolations.

Speaker: Leonardo Cosmai (INFN Bari)

Slides cosmai.pdf

128 Hadron properties at finite temperature and density with two-flavors of Wilson fermion

Spatial meson correlators at finite temperature are studied on lattice QCD. Two-flavor gauge configurations of 16^3*4 lattice with the RG improved gluon action and the clover-improved Wilson quark action, generated by WHOT-QCD collaboration, are employed [1]. The simulations are performed along the lines of constant physics, on which the mass ratio of pseudo-scalar meson to vector meson, m_{PS}/m_V, is kept constant. The temperatures of the simulation in the unit of the pseudo-critical temperature, T/T_{PC}, are in the range 0.76-4.0 for m_{PS}/m_V=0.65 and 0.80. Screening masses of the mesons at finite temperature are extracted from the spatial meson correlators. Next, meson properties at finite temperature and density are studied by using the Taylor expansion with respect to quark chemical potential. Responses of spatial meson correlators to quark chemical potential are calculated up to second order. The shifts of meson screening masses due to medium effect are obtained from the responses. Based on these results, meson properties at finite temperature and density are discussed. Reference: [1] Y.Maezawa et al. (WHOT-QCD Collaboration), Phys. Rev. D75, 074501 (2007).

Speaker: Hideaki Iida (Hashimoto Mathematical Physics Laboratory, Nishina Center, RIKEN, Japan)

Slides iida.pdf

129 QCD at finite chemical potential in a small hyperspherical box

We consider the phase diagram of QCD formulated in small spatial volumes. The benefit of the small spatial volume is that it allows for a perturbative calculation of the phase diagram which is valid for all temperatures and densities. The action of QCD is complex when the quarks are coupled to a non-zero chemical potential. This results in the sign problem which prevents lattice simulations using conventional techniques. From one-loop perturbation theory on S^1 x S^3 we calculate the phase diagram analytically in the T − mu plane in the large N and Nf limit by generalizing the matrix model technique of Gross and Witten for the case of a complex action. We compare with low temperature results for N = 3 obtained by performing the integrals over the gauge fields numerically. We calculate expectation values for several observables including the fermion number and the Polyakov loop (and its dagger which differs at non-zero chemical potential). For the fermion number an atomic-level-type structure is observed as a function of the chemical potential and each level transition coincides with a spike in the Polyakov loop and it’s dagger, indicating partial-filling of the level. In the large N limit each level transition corresponds to discontinuities in the fermion number which result in third-order transitions of the Gross-Witten type. We confirm the appearance of the level-structure at low temperatures in lattice simulations of 2-color QCD where the sign problem is absent.

Speaker: Joyce Myers (Swansea University)

Slides myers.pdf

Parallel 29: Weak decays and matrix elements

130 $B \to D^*l\nu$ at zero recoil: an update

We present an update of our calculation of the form factor for $B\to D^* l \nu$ at zero recoil, with higher statistics and further, finer, lattices. As before, we use the Fermilab action for $b$ and $c$ quarks, the asqtad staggered action for light valence quarks, and the MILC ensembles for gluons and light quarks (L\"uscher-Weisz married to 2+1 rooted staggered sea quarks).

Speaker: Andreas S. Kronfeld (Fermilab)

Slides kronfeld.pdf

131 D to K semi-leptonic form factors from HISQ light and charm quarks

We investigate D to Kl\nu semi-leptonic decays using HISQ light and charm quarks on the MILC coarse and fine lattices. Using PCVC allows us to extract the form factors with no need for operator renormalization. We employ random-wall sources and simultaneous multi-T fits, in order to reduce the statistical errors. By caring out consistency checks, we successfully re-produce all meson spectrum and decay constants related to this process. Chiral and continuum extrapolations are done using partially quenched ChiPT, and systematic errors are carefully estimated. We present preliminary results for f_+(q^2=0), f_0(q^2), f_+(0)/f_{D_s} and |V_{cs}|.

Speaker: Heechang Na (The Ohio State University)

Slides heechang.pdf

132 Form factors of the D -> pion and D -> K semileptonic decays

We present lattice results for the form factors relevant in the D -> pion and D -> K semileptonic decays obtained from simulations with two flavors of dynamical twisted-mass fermions. Results at four values of the lattice spacing, ranging from ~ 0.05 up to ~ 0.1 fm, allow a careful study of the discretization effects. The application of Heavy Meson Chiral Perturbation Theory provides an extrapolation of our results for both the scalar and the vector form factors to the physical point with quite good accuracy, obtaining a nice agreement with the experimental data.

Speaker: Stefano Di Vita (University of Rome III and INFN - Roma Tre)

Slides divita.pdf

133 Semileptonic decays of K and D mesons in 2+1 flavor QCD

The experimentally measured rates of the semileptonic decays K to pi l nu and D to K(pi) l nu can be combined with lattice calculations of the associated form factors to precisely extract the CKM matrix elements |V_{us}| and |V_{cs(d)}|. We report on the status of form factor calculations with Fermilab charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC ensembles. Analyses of the data for the charm decays indicate significant improvements in the statistical uncertainties. We discuss the use of hisq valence quarks to calculate the K to pi l nu form factor f_+(0) and describe tests of our method.

Speaker: Elvira Gamiz (Fermilab)

Slides gamiz.pdf

134 SU(2) ChPT analysis of the scalar and vector form factors of the kaon semileptonic decay obtained from twisted-mass fermions with Nf = 2

We investigate the form factors relevant in the K -> pion semileptonic decays using maximally twisted-mass fermions with two flavors of dynamical quarks. The simulations cover pion masses as light as 260 MeV and four values of the lattice spacing, from ~ 0.05 up to ~ 0.1 fm, which allow to compute accurately the continuum limit. SU(2) Chiral Perturbation Theory is applied to the extrapolation of the form factors to the physical point with their full momentum dependence. Our results are compared with the experimental data for the extraction of the Cabibbo angle |V_{us}|.

Speaker: Lorenzo Orifici (University of Rome III and INFN - Roma Tre)

Slides orifici.pptm

Parallel 31: Vacuum structure and confinement

135 Lattice Index Theorem and Fractional Topological Charge

We study topological properties of classical spherical center vortices from the low-lying eigenmodes of the Dirac operator, in both the overlap and asqtad formulations, fundamental and adjoint representation. In particular we address the puzzle raised in a previous work of our work group\ [Phys. Rev. D 77, 14515 (2008)], where we found a violation of the lattice index theorem with the overlap Dirac operator even for "admissible" gauge fields. We confirm the discrepancy between the topological charge and the index of the Dirac operator also for the other, above mentioned representations. Furthermore we find some evidence for fractional topological charge during cooling the spherical center vortex on a $40^3\times2$-lattice. The object with topological charge $Q=1/2$ we identify as a Dirac monopole with a gauge field fading away at large distances. Therefore even for periodic boundary conditions it does not need an antimonopole.

Speaker: Roman Höllwieser (VUT)

Slides 1_Hoellwieser.pdf

136 NSPT study of the three-loop lattice gluon propagator in Landau gauge

By means of Numerical Stochastic Perturbation Theory (NSPT), we investigate the lattice gluon propagator up to the third loop in the limit of infinite volume and at vanishing lattice spacing. Based on known anomalous dimensions and a parametrization of both the hypercubic symmetry group H(4) and finite-size effects, we calculate the non-logarithmic contributions iteratively starting with the first-loop expression.

Speaker: Christian Torrero (University of Regensburg)

Slides 2_Torrero.pdf

137 Probing the Yang-Mills vacuum with adjoint zero-modes

We analyse in detail a filtering method proposed by Gonzalez-Arroyo and Kirchner to eliminate ultra-violat noise and probe the topological content of Monte-Carlo ensembles. The proposal is based on looking for the low lying eigen-modes of a super-symmetric operator constructed from a projection of the adjoint-Dirac operator. For classical configurations the density of these modes provides a direct estimate of the self-dual and anti-self-dual part of the gauge action density. We test the performance of the proposal on a set of prepared configurations including both smooth and heated instantons, and instanton-antiinstanton pairs. For this, the super-symmetric operator is implemented on the lattice through a projection of the Neuberger-Dirac operator. A detailed analysis of finite volume and lattice artifacts is presented. We will also show preliminary results of the application of the method to the analysis of Monte Carlo configurations.

Speaker: Alfonso Sastre (IFT-UAM/CSIC)

Slides 3_sastre.pdf.pdf

138 The deconfinement transition in 2+1 dimensional SU(3) from twisted boundary conditions and self-duality

We study the pure SU(3) lattice gauge theory in 2+1 dimensions using 't Hooft's twisted boundary conditions to force non-vanishing center flux through the finite box. In this way we measure the free energy of spacelike center vortices as an order parameter for the deconfinement transition. The transition is of second order and by the Svetitsky-Jaffe conjecture it falls into the universality class of the 2d 3-state Potts model. Of particular importance for us is the self-duality of the 2d q-state Potts models which can be generalized to hold in a finite volume for any q. We verify the corresponding self-duality for SU(3) and exploit it to extract critical couplings with high precision from numerical simulations in rather small volumes. We furthermore obtain estimates for critical exponents and the critical temperature in units of the dimensionful continuum coupling. Finally we present preliminary results from applying the same methods to the SU(4) gauge theory in 2+1 dimensions.

Speaker: Nils Strodthoff (Institut fuer Kernphysik, TU Darmstadt)

Slides 4_Strodthoff.pdf

139 Exploring center symmetry with electrically charged quarks

In pure SU(N) gauge theory, the deconfinement phase transition is tied to the spontaneous breaking of center symmetry. The expectation value of the Polyakov jumps from zero to a finite value at T_c, which coincides with the suppression of spacelike center vortices. Center symmetry is lost, however, with the introduction of dynamical quarks, and this picture evaporates with it. Still, since quarks carry fractional electric charge, a center transformation may be compensated by an appropriate U(1) phase. The true gauge group of the Standard Model is in fact SU(3)xSU(2)xU(1)/Z_6, with Z_6 representing this hidden global symmetry. As a first step towards studying the relevance of this symmetry and the corresponding vortices to confinement and the phase structure of the Standard Model, we consider SU(2)xU(1)/Z_2 with two flavors of dynamical Wilson fermions to model quarks in two-color QCD with electromagnetism.

Speaker: Sam R Edwards (Institut für Kernphysik, TU-Darmstadt)

Slides 5_edwards.pdf

Parallel 33: Hadron spectroscopy

140 2+1 flavor DWF QCD and almost physical pion masses

We are producing 2+1 flavor DWF ensembles with dynamical pion masses of 180 and 250 MeV, a volume of (4.5 fm)^3 and 1/a = 1.4 GeV, using the Iwasaki plus DSDR (Dislocation Suppressing Determinant Ratio) gauge action. Basic properties of these ensembles and their production are discussed. We report on measurements of pseudoscalar masses and decay constants on these ensembles, with valence pions as light as 145 MeV. These observables are fit to SU(2) ChPT jointly with our similar results from finer lattices using 2+1 flavor DWF plus the Iwasaki action, to get better control over the combined chiral and continuum extrapolation.

Speaker: Robert Mawhinney (Columbia University)

Slides Mawhinney_Lat2010.pdf

141 Strange quark content of nucleon via reweighting on (2+1)-flavor Domain Wall Fermion lattices

The slope of nucleon mass with respect to the dynamical strange quark mass is directly related to the strange quark content of nucleon ($\langle N | \bar{s}s | N \rangle $). This slope can be calcuated by shifting of dynamical strange quark mass via reweighting on dynamical ensembles, which allows a relatively inexpensive evaluation of the quantity without direct evaluation of disconnected diagrams. Calculation of $\langle N | \bar{s}s | N \rangle $ on $a^{-1} \sim$ 1.7 and 2.3 Gev (2+1) flavor dynamical Domain Wall Fermion ensembles RBC/UKQCD collaborations generated are reported.

Speaker: Chulwoo Jung (Brookhaven National Laboratory)

Slides jung.pdf

142 Sigma term and strange content of the nucleon

The sigma term and strange content of the nucleon play an important role in hadronic physics and dark matter detection. Preliminary results for these quantities, obtained from 2+1 flavor lattice QCD simulations, will be presented. Emphasis will be put on controlling and quantifying systematic errors. This work is performed as part of a Budapest-Marseille-Wuppertal + Regensburg collaboration.

Speaker: Alberto Ramos (Centre de Physique Theorique, Marseille (CNRS))

Slides talk.pdf

143 Flavour Symmetry and Flavour Symmetry Breaking in 2+1 Flavour lattice simulations

The QCD interaction is flavour-blind. Neglecting electromagnetic and weak interactions, the only difference between flavours comes from the mass matrix. We investigate how flavour-blindness constrains hadron masses after flavour SU(3) is broken by the mass difference between the strange and light quarks, to help us extrapolate 2+1 flavour lattice data to the physical point. We have our best theoretical understanding when all three quark flavours have the same masses (because we can use the full power of flavour SU(3)); nature presents us with just one instance of the theory, with m_s/m_l ~ 25. We are interested in interpolating between these two cases. We consider possible behaviours near the symmetric point, and find that flavour blindness is particularly helpful if we approach the physical point along a path with m_u + m_d + m_s held constant. We also show that on this trajectory the errors of the partially quenched approximation are much smaller than on other trajectories.

Speaker: Paul Rakow (University of Liverpool)

Slides RakowLat10.pdf

144 Tuning the strange quark mass and the hadron mass spectrum for 2+1 quark flavours

QCD lattice simulations with 2+1 flavours typically start at rather large up-down and strange quark masses and extrapolate first the strange quark mass to its physical value and then the up-down quark mass. An alternative method of tuning the quark masses is discussed here in which the singlet quark mass is kept fixed, which ensures that the kaon always has mass less than the physical kaon mass. It can also take into account the different renormalisations (for singlet and non-singlet quark masses) occurring for non-chirally invariant lattice fermions and so allows a smooth extrapolation to the physical quark masses. This procedure enables a wide range of quark masses to be probed, including the case with a heavy up-down quark mass and light strange quark mass. Numerical results show the correct order for the baryon octet and decuplet spectrum and an extrapolation to the physical pion mass gives mass values to within a few percent of their experimental values.

Speaker: Roger Horsley (University of Edinburgh)

Slides talk_rhorsley_lat10.pdf

Parallel 35: Theoretical developments

145 Near-Integrability of Yang-Mills Theories

Gauge theories with some or all of space-time discretized may be recast as coupled integrable 1+1-dimensional field theories, whose exact S-matrices and form factors are known. Information about the 1+1-dimensional system can be used to extract string tensions and mass spectra for weakly-coupled (but anisotropic) 2+1-dimensional gauge theories. For 3+1-dimensional gauge theories, weak-coupling assumptions no longer work as effectively, but a qualitative string-parton picture appears. I will discuss briefly how the methods may be extended, in principle, to the isotropic case.

Speaker: Peter Orland (Baruch, CUNY)

Slides OrlandLatt2010.pdf

146 Very high order lattice perturbation theory for Wilson loops

Employing the method of numerical stochastic perturbation theory we compute Wilson loops $W_{NM}$ of moderate sizes $N \times M$ up to loop order $n=20$. Results are presented for both plaquette and tree-level Symanzik gauge actions. Based on a hyperbolic fit ansatz we investigate the convergence behaviour on finite lattice sizes for both actions. It is shown that boosted perturbation theory improves the convergence of the series significantly for the Wilson gauge action. We compute the dependence of the difference with the Monte Carlo results ($\delta W_{11}=W_{11,PT}-W_{11,MC}$) on the lattice spacing $a$. Our data show that with inceasing loop order $n$ the magnitude of a spurious term proportional to $a2$ strongly decreases. We give some estimate to the gluon condensate $$.

Speaker: Holger Perlt (Institute for Theoretical Physics, Leipzig University)

Slides Talk_Perlt.pdf

147 Glueball masses with exponentially improved statistical precision

We briefly review the computational strategy we have recently introduced for computing glueball masses and matrix elements, which achieves an exponential reduction of statistical errors compared to standard techniques. The global symmetries of the theory play a crucial role in the approach. We show how our previous work on parity can be generalized to other symmetries. In particular we discuss how to extract the mass of the 0++, 2++ and 0-+ lightest glueballs avoiding the exponential degradation of the signal to noise ratio. We present new numerical results and update the published ones.

Speaker: Michele Della Morte (Institut fuer Kernphysik, Mainz)

Slides DellaMorte.pdf

148 5-dimensional SU(2) lattice gauge theory with Z_2 orbifolding and its phase structure

In 5-dimensional SU(2) lattice gauge theory with Z_2 orbifolding, we find a new symmetry. It helps us to recognize the Polyakov loop as the order parameter, because the center symmeter is trivial and useless for the loop in the system. The vacuum structure and the application of the symmetry are also discussed.

Speaker: Hiroto So (Ehime University)

Slides lat2010-talk-so.pdf

149 Second Order Phase Transition in Anisotropic Lattice Gauge Theories with Extra Dimensions

Field theories with extra dimensions live in a limbo. While their classical solutions have been the subject of considerable study, their quantum aspects are difficult to control. A special class of such theories are anisotropic gauge theories. The anisotropy was originally introduced to localize chiral fermions. Their continuum limit is of practical interest and it will be shown that the anisotropy of the gauge couplings plays a crucial role in opening the phase diagram of the theory to a new phase, that is separated from the others by a second order phase transition. The mechanism behind this is now understood and is, indeed, generic for a certain class of models, that can be studied with lattice techniques. This leads to new perspectives for the study of quantum effects of extra dimensions.

Speaker: Stam NICOLIS (CNRS-LMPT Tours)

Slides Nicolis.pdf

16:10 Coffee break

Parallel 26: Hadronic structure and interactions

150 Nucleon strange quark content in 2+1 flavor QCD

We calculate the nucleon strange quark content in 2+1 flavor QCD using the overlap fermion for both sea and valence quarks. The disconnected three-point function is directly calculated using the all-to-all propagator. We emphasize the role of chiral symmetry in the renormalization of the strange quark content.

Speaker: Kohei Takeda (University of Tsukuba)

Slides takeda.pdf

151 Strangeness in the nucleon from a mixed action calculation

Both the scalar strange content of the nucleon, as embodied in the F_Ts parameter, as well as the strange quark contribution to nucleon spin, Delta s, are investigated in a mixed action scheme employing domain wall valence quarks and quark loops on MILC asqtad dynamical fermion ensembles. Results are presented for pion masses 495 MeV and 356 MeV.

Speaker: Michael Engelhardt (New Mexico State University)

Slides talk_engelhardt_revised.pdf

152 Improved method for computing nucleon strangeness

The strange quark content of the nucleon, <N|ss|N>, as well as other matrix elements, can be calculated on the lattice by examining correlations between the nucleon propagator and the quark condensate. The largest contribution to statistical error comes from coincidental correlations between the propagator and fluctuations in the condensate far from the propagation region that contribute only noise. We will present a technique for considering only the condensate near the propagation region, significantly reducing the statistical error.

Speaker: Walter Freeman (University of Arizona)

Slides freeman.pdf

Parallel 28: Nonzero temperature and density

153 Study of finite temperature QCD with 2+1 flavors via Taylor expansion and imaginary chemical potential

We study QCD with 2+1 flavors at nonzero temperature and nonzero chemical potential. We present preliminary results obtained from lattice calculations performed with an improved staggered ferminios action (p4-action) on lattice with temporal extent N_t = 4 on a line of constant physics with the strange quark mass adjusted to its physical value and the pion mass of about 220 MeV. We focus our study on a range of temperatures 0.937 < T/T_c < 1.072.

Speaker: Rossella Falcone (Bielefeld Universitaet, Germany)

Slides falcone.pdf

154 Chiral and deconfinement transitions in strong coupling lattice QCD

We investigate the QCD phase diagram based on the strong coupling lattice QCD. In particular, we focus on the interplay between the chiral and deconfinement transitions in the strong coupling framework. We show that the critical temperature at zero chemical potential becomes lower and closer to Mont-Carlo data due to the Polyakov loop effects. We will show some results on finite chemical potential cases.

Speaker: Kohtaroh Miura (Yukawa Institute for Theoretical Physics, Kyoto University)

Slides miura.pdf

155 Effective Potential and Phase Diagram in the Strong-Coupling Lattice QCD with Next-to-Next-to-Leading Order and Polyakov Loop Effects

Strong Coupling Lattice QCD (SC-LQCD) is a method directly based on QCD, and has been applied to investigate the properties of the QCD phase diagram in the finite chemical potential region. The previous studies in next-to-leading order (NLO) evaluation assert that the effect of NLO in the effective potential are renormalized in modification of the quark mass and chemical potential in the strong coupling limit (SCL), and two order parameters (the chiral condensate and density) are found to appear. These studies indicate the possibility of the partially chiral restored phase as well. In this study, we evaluate the effective potential in the strong-coupling lattice QCD including next-to-next-to-leading order and Polyakov loop effects. We also discuss the properties of the QCD phase diagram by using the effective potential, including the critical temperature and the position of the critical point. We find that the critical point is sensitive to the NNLO effects. We also find that the critical temperature of the chiral phase transition is close to Monte Carlo results due to Polyakov loop effects at \beta = 2Nc / g^2 ~ 4 and the critical temperature of the chiral and deconfinement phase transition have almost the same values.

Speaker: Takashi Nakano (Yukawa Institute of Theoretical Physics, Kyoto university)

Slides nakano.pdf

156 Thermodynamic quark susceptibilties in the PNJL model

The Monte-Carlo method is applied to the Polyakov-loop extended Nambu–Jona-Lasinio (PNJL) model. This allows to go beyond the saddle-point approximation in a mean-field calculation and introduces fluctuations around the mean fields. We study the impact of fluctuations on the thermodynamics of the model, in the two quark flavors case. We calculate the second order Taylor expansion coefficients of the thermodynamic grand canonical partition function with respect to quark chemical potential and present a comparison with extrapolations from lattice QCD. We show that fluctuations are necessary in order to reproduce lattice data for the flavor non-diagonal expansion coefficients. Of particular importance are pion fields, the contribution of which is found to be highly volume dependent. This opens the question of what would be the behavior of such quantities on the lattice, in the infinite volume limit.

Speaker: Marco Cristoforetti (ECT*)

Slides cristoforetti.pdf

Parallel 30: Weak decays and matrix elements

157 A Progress Report on B^0 Mixing

We give a progress report on the calculation of B^0 mixing matrix elements, focusing on contributions that could arise beyond the Standard Model. The calculation uses asqtad (light quark) and Fermilab (heavy quark) valence actions and MILC ensembles with 2+1 flavors of asqtad sea quarks.

Speaker: Christopher Bouchard (U. of Illinois)

Slides bouchard.pdf

158 B-physics with dynamical domain-wall light quarks and relativistic b-quarks

We report on our progress in calculating the B-meson decay constants and B^0-bar B^0 mixing parameters using domain-wall light quarks and relativistic b-quarks. We present our computational method and show some preliminary results obtained on the coarser (a approx 11fm) 24^3 lattices. This work is presented for the RBC and UKQCD collaborations.

Speaker: Oliver Witzel (Brookhaven National Laboratory)

Slides witzel.pdf

159 Neutral B meson mixing with 2+1 flavor domain-wall light and static heavy quarks

The B^0--anti-B^0 mixing parameter for the B_d and B_s meson is calculated using the domain-wall fermions (DWF) for the light quarks and improved static fermions for the b quark on the 1/a=~1.7 GeV n_f=2+1 Iwasaki-DWF ensembles. The static approximation has the sizable Lambda/m_h leading systematic error. The systematic error for the SU(3)_f breaking ratio, however, is suppressed by another factor of (m_d-m_s)/Lambda, thus is 2% with a naive estimate. The results will eventually be combined with those on a finer lattice to have continuum extrapolation, where the use of two different smearings in the static quark action and the O(g^2 a) improvement of the operators will provide various cross checks.

Speaker: Yasumichi Aoki (RIKEN BNL Research Center)

Slides aoki.pdf

Parallel 32: Standard model parameters and renormalization

160 Ghost-gluon coupling power corrections and $\Lambda_{\overline{MS}}$ from twisted-mass lattice QCD at $N_f=2$.

I present results concerning the non-perturbative evaluation of the ghost-gluon running QCD coupling constant from $N_f=2$ twisted-mass lattice calculations. Special attention is payed to the treatment of artifacts, in particular the quark mass, and to the different sources of systematical uncertainties. The value of $\Lambda_{\overline{MS}}$ is computed revealing the presence of a dimension-two $\langle A^2 \rangle$ gluon condensate.

Speaker: Mario Gravina (LPT - Universite Paris 11, Orsay (France))

Slides gravina_lat2010.pdf

161 Running of the Schroedinger functional coupling with four massless flavours

I discuss the status of different determinations of alpha_s, motivating a precise and reliable computation from lattice QCD. In order to suppress perturbative errors, the non-perturbative computation has to reach high energy scales mu. Such results already exist in the SF-scheme for Nf=0,2,3 . We now add the running with four massless flavours in a range of alpha from about 0.07 to 0.3 . It is based on our recent determination of the Sheikholeslami Wohlert coefficient in the four-flavour theory.

Speaker: Rainer Sommer (NIC, DESY)

Slides sommer_lat10rs.pdf

162 Non-perturbative running of the coupling from four-flavour lattice QCD with staggered quarks

Using the Schroedinger functional (SF) with a single staggered fermion field we calculate the SF coupling in four-flavour QCD for a wide range of energies and lattice sizes up to $L/a=16$. Preliminary results for the continuum extrapolation of the step-scaling function are presented. To reduce cutoff effects, one-loop ${\rm O}(a)$ improvement has been implemented. Various cross checks are made possible by the use of two independent sets of lattices with either $T=L+a$ or $T=L-a$.

Speaker: Paula Perez Rubio (Universidad Autonoma de Madrid and Trinity College Dublin)

Slides perez_rubio_lat_talk.pdf

Parallel 34: Hadron spectroscopy

163 New developments in multi-meson systems

Recent developments in calculations of systems of large numbers of mesons are presented. A recursive algorithm is developed to calculate correlation functions for systems involving very large numbers of mesons. This algorithm scales linearly in the number of mesons and allows for previous calculations of n<13 meson systems to be extended. Recent numerical investigations of the spectrum of mixed systems of n pions and m kaons are presented for n+m < 13. The measured energies are used to extract the 3 two-body and 4 three-body interactions between pions and kaons.

Speaker: William Detmold (Jefferson Laboratory)

Slides 1_Detmold.pdf

164 A novel method for evaluating hadronic correlation functions in Lattice QCD spectroscopy.

We describe a new method for evaluating hadronic correlation functions, which combines Laplacian Heaviside (Laph) quark-field smearing with a stochastic estimator. The algorithm utilizes noise dilution in a new way to reduce the variance in euclidean-time correlators. This approach to correlator evaluation facilitates precision studies of the hadron spectrum, including flavor-singlet mesons and multi-particle states, on realistic lattice volumes.

Speaker: Justin Foley (Carnegie Mellon University)

Slides 2_jfoley.pdf

165 First Applications of the Stochastic LapH method in Lattice QCD Spectroscopy

A novel algorithm which combines the LapH method of evaluating quark-field propagation with a stochastic estimator is tested on a range of hadronic correlators. The results demonstrate the advantage of this new method over the ordinary LapH method, particularly for the evaluation of flavor-singlet meson and multi-particle correlators, which are challenging for the ordinary LapH method. Future applications will also be discussed.

Speaker: Chik Him Wong (Carnegie Mellon University)

Slides 3_chwong.pdf

166 Phase Shift with LapH Propagators

The pion-pion scattering phase shift on anisotropic, dynamical lattices will be presented. The LapH method for computing quark propagators is used to form the two-particle correlation function with a number of different operators. The phase shift is computed using Luescher's finite volume method for pion masses near 390 MeV on 2+1 dynamical lattices.

Speaker: Keisuke Juge (University of the Pacific)

Slides 4_Juge.pdf

Parallel 36: Theoretical developments

167 Worm algorithm for the O(N) Gross-Neveu model

We study the lattice O(N) Gross-Neveu model with Wilson fermions in the loop gas formulation. Employing the Prokof'ev-Svistunov worm algorithm we can simulate fluctuating fermionic boundary conditions and use them to tune the system exactly to the critical point. We show how the worm algorithm can be extended to sample directly the correlation functions of fermion bound states involving an arbitrary number of Majorana fermions and present results for various observables.

Speaker: Vidushi Maillart (University of Bern and Regensburg)

Slides Lattice_conf_2010_vmaillart.pdf

168 Loop gas formulation of supersymmetric quantum mechanics

We discuss the formulation of supersymmetric quantum mechanics on the lattice as an interacting gas of bosonic and fermionic loops and its simulation using the Prokof'ev-Svistunov worm algorithm. In the case of unbroken supersymmetry we can simulate different lattice discretisations, including Q-exact actions, in the weak and strong coupling regime, and we find that the expected mass degeneracy between the bosonic and fermionic sector is reproduced with very high precision. Further, we also address the case of broken supersymmetry and discuss implications and consequences for the simulation with the worm algorithm.

Speaker: David Baumgartner (University of Bern)

Slides Baumgartner_Lattice_2010.pdf

169 Loop gas formulation of supersymmetric models in low dimensions

We review the construction of twisted supersymmetry and Q-exact actions on the lattice in low dimensions and discuss the formulation of such supersymmetric lattice models as an interacting gas of bosonic and fermionic loops. We comment on the relevance of the fermion sign problem for the vanishing of the Witten index and show how this sign problem can be solved by employing the Prokof'ev-Svistunov worm algorithm together with topological boundary conditions.

Speaker: Urs Wenger (Institute for Theoretical Physics, University of Bern)

Slides lattice10_wenger.pdf

Poster session

170 $K^0-\bar{K}^0$ mixing beyond the SM from $N_f=2$ tmQCD

We present preliminary results on the of neutral kaon oscillations in extensions of the Standard Model. Using $N_f=2$ maximally twisted sea quarks and Osterwalder-Seiler valence quarks, we achieve both O(a)-improvement and continuum-like renormalization pattern for the relevant four-fermion operators. We perform simulations at three values of the lattice spacing and extrapolate/interpolate our results to the continuum limit and physical light/strange quark mass. The calculation of the renormalization constants of the complete operator basis is performed non- perturbatively in the RI-MOM scheme.

Speaker: PETROS DIMOPOULOS (University of Rome 'La Sapienza')

171 $N_c =2$ lattice gauge theories with fundamental and adjoint Wilson fermions

We investigate the Nc=2 lattice gauge theories with two flavors of the Wilson fermions (and twisted mass ghosts) in fundamental and adjoint representations. The phase structure of these theories is studied in the coupling-quark mass plane by observing meson correlation functions and spectral density of the Dirac operator.

Speaker: Hideo Matsufuru (High Energy Accelerator Research Organization (KEK))

172 $O(\aplha_L^2)$ perturbative Green's functions of the fermion propagator, and of local and extended fermion bilinear operators, with Symanzik improved gluons and SLiNC fermions.

In this work we compute the one-loop 1PI 2-point perturbative bare Green's functions of: - The fermion propagator $\bar{\Psi} \Psi$ - Local fermion bilinear operators $\bar{\Psi} \Gamma \Psi$ - Extended fermion bilinear operators $\bar{\Psi} \Gamma_{\{\mu} \overleftrightarrow{D}_{\nu\}} \Psi$ where $\Gamma$ corresponds to the Dirac operators and $\overleftrightarrow{D} = \frac{1}{2}\left( \overrightarrow{D} - \overleftarrow{D} \right)$, in the lattice formulation of QCD. The calculation is carried out up to $O(\alpha_L^2)$ ($\alpha_L$: lattice spacing). We employ the Symanzik improved gauge actions and stout link clover (SLiNC) fermions. Our results are given as a polynomial in $c_{SW}$ ($c_{SW}$: clover parameter) in terms of the bare coupling constant. The gauge parameter $\alpha$, the SLiNC parameter $\omega$, the Symanzik coefficients $c_i$, the fermion masses $m_i$ and the number of colors $N_c$ are kept as free parameters.

Speaker: Apostolos Skouroupathis (University of Cyprus, Department of Physics)

173 A web-based visualization tool for lattice QCD

Vis is a system that implements Software as a Service for Lattice QCD computations. At its core it is a repository of gauge confurations with web and web services interfaces. It gives users the ability to queue tasks and execute them in background. Tasks can be FermiQCD program and/or visualization algorithms (topological charge, polyakov lines, evergy density, etc.). The web services are accessible from a comman line script that allows for example, to upload all gauge configurations in the current folder and request the server to make a plot of the average plaquette and generate a movie of the topological charge. It interfaces with VisIt (also running serverside) for 3D visualizations and matplotlib for 2D plots. Data and results are automatically posted online and controlled by a role based access control mechanism. All major tasks can be executed directly from the web interface.

Speaker: Massimo Di Pierro (DePaul University)

174 Absolute Measure of Local Chirality and the Chiral Polarization Scale of the QCD Vacuum

We champion use of the absolute measure of local chirality since it has a uniform distribution for randomly reshuffled chiral components so that any deviations from uniformity in the associated "X-distribution" are directly attributable to QCD-induced dynamics. We observe a transition in the qualitative behavior of the absolute X-distribution of low-lying eigenmodes which, we propose, defines a chiral polarization scale of the QCD vacuum.

Speaker: Terrence Draper (University of Kentucky)

175 AuroraScience: Supercomputing for LQCD.

This poster covers in details the architecture of the application-driven AuroraScience supercomputer. This machine is a large 3D array of latest generation Intel processors, with nearest-neigbor processors connected by a network with toroidal topology. Each node has a peak (double precision) performance of 100-150 Gflops. This machine has been engineered to be reliably assembled in thousands of nodes, making it possible to deploy systems with a peak performance of several hundred Tflops. This poster complements a companion talk, presented by L. Scorzato, focusing on the use of this system as an LQCD-optimized number cruncher. Here, we focus on the structure of the machine and -- in greater details -- on the toroidal interconnection system.

Speaker: marcello pivanti (INFN and University of Ferrara)

176 Better HMC integrators for dynamical simulations

We show how to improve the molecular dynamics step of HMC, both by tuning the integrator using Poisson brackets measurements and with the use of force gradient integrators. We show results for moderate lattice sizes.

Speakers: Anthony Kennedy (University of Edinburgh), Bálint Joó (JLab), Mike Clark (Harvard University), Paulo Silva (Universidade de Coimbra)

177 BQCD -- Berlin quantum chromodynamics program

BQCD is a Hybrid Monte-Carlo program that simulates lattice QCD with dynamical Wilson fermions. The development of BQCD began in Berlin in 1998 for studies of parallel tempering and the Aoki phase. For ten years BQCD has been one of the main production programs of the QCDSF collaboration. The program has been ported to and optimised for different massively parallel machines, for instance QPACE. The code is written mainly in Fortran. We have implemented 2 and 2 + 1 fermion flavours with pure, clover improved, and stout smeared fat link Wilson fermions as well as standard plaquette, and an improved (rectangle) gauge action. The single flavour is simulated with the RHMC algorithm. BQCD is free software under the GNU General Public License. It can be downloaded from http://www.zib.de/stueben/bqcd.

Speaker: Hinnerk Stueben (Konrad-Zuse-Zentrum fuer Informationstechnik Berlin (ZIB))

178 Chiral symmetry of QCD with 12 light flavors

We study QCD with 12 light flavors at intermediate values of the bare lattice coupling. We contrast and compare the results for the chiral condensate and the the pion mass with different theoretical models motivated by the physics of the Goldstone phase and universal properties of chiral symmetry breaking. Our analysis favors chiral symmetry restoration.

Speaker: Maria Paola Lombardo (INFN)

179 Comparison between LQCD and PNJL model at finite chemical potentials

Lattice QCD (LQCD) has the sign problem at real quark chemical potential. There are some regions with no sign problem; one is the imaginary quark chemical potential region and another is the real and imaginary isospin chemical potential regions. We show that the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model can reproduce LQCD data in the regions. We also determine the parameters of the model from the data and predict the QCD phase diagram in the real quark chemical potential region. The PNJL model can also reproduce LQCD data on the average phase factor at small real quark chemical potential, when temperature is smaller than the critical temperature.

Speaker: Yuji Sakai (Kyushu University)

180 Comparison of mass preconditioned HMC and DD-HMC algorithm for two-flavour QCD

Mass preconditioned HMC and DD-HMC are among the most popular algorithms to simulate improved Wilson fermions. We present a comparison of the performance of the two algorithms for realistic quark masses and lattice sizes.

Speaker: Marina Marinkovic (Humboldt University Berlin)

181 Critical behavior of the compact 3D U(1) gauge theory at finite temperature

Critical properties of the compact three-dimensional U(1) lattice gauge theory are explored at finite temperatures. The critical point of the deconfinement phase transition, critical indices and the string tension are studied numerically on lattices with temporal extension Nt = 8 and spatial extension ranging from L = 32 to 256. The critical indices, which govern the behaviour across the deconfinement phase transition, are generally expected to coincide with the critical indices of the two-dimensional XY model. It is found that the determination of the infinite volume critical point differs from the pseudo-critical coupling at L = 32, found earlier in the literature and implicitly assumed as the onset value of the deconfined phase. The critical index nu computed from the scaling of the pseudocritical couplings agrees well with the value nu = 1/2 of the XY model. The computation of the index eta brings to a value larger than expected. The possible reasons for such behaviour are discussed.

Speakers: Alessandro Papa (Università della Calabria and INFN), Mario Gravina (Laboratoire de Physique Théorique, Université de Paris-Sud 1, Orsay1), Roberto Fiore (Università della Calabria and INFN)

182 Critical properties of the two-dimensional Z(5) vector model

The 2D Z(5) vector model is investigated through the determination of critical points and various critical indices. To this purpose, a new cluster algorithm has been developed for 2D Z(N) models with odd values of N. Results are compared with analytical predictions.

Speaker: Gennaro Cortese (Università della Calabria and INFN-Cosenza)

183 Curvature of the chiral critical line in the T-\mu plane

We discuss the universal properties of the QCD chiral transition for both zero and small but non-zero chemical potential. We outline how those universal properties can be used to extract the curvature of the line of chiral transitions in the T-\mu plane for small chemical potential. We present evidence of these universal properties and result for this curvature obtained using lattice simulations with improved staggered fermions.

Speaker: Swagato Mukherjee (Assistant Physicist)

184 Definition of Instantons in Noncommutative Gauge Theory in Higher Dimensions

Theories with noncommutative space-time coordinates represent alternative candidates of grand unified theories. We discuss U(1) gauge theory in 2 and 4 dimensions on a lattice with N sites. The mapping to a U(N) plaquette model in the sense of Eguchi and Kawai can be used for computer simulations. In 2D it turns out that the formulation of the topological charge leads to the imaginary part of the plaquette. Concerning 4D, the definition of instantons seems straightforward. One can transcribe the plaquette and hypercube formulation to the matrix theory. The transcription of a monopole observable seems to be difficult. The analogy to commutative U(1) theory of summing up the phases over an elementary cube does not obviously transfer to the U(N) theory in the matrix model. It would be interesting to measure the topological charge on a noncommutative hypercube.

Speaker: Harald Markum (Vienna University of Technology)

185 Double pass variants for multi-shift BiCGStab(l)

In analogy to Neubergers double pass algorithm for the Conjugate Gradient inversion with multi-shifts we introduce a double pass variant for BiCGstab(l). A possible application is the Overlap Operator of QCD at non-zero chemical potential, where the kernel of the sign function becomes non-Hermitian. The sign function can be replaced by a partial fraction expansion, requiring multi-shift inversions. We compare the performance of the new method with other available algorithms, namely partial fraction expansions with restarted FOM inversions and the Krylov-Ritz method using nested Krylov subspaces.

Speaker: Simon Heybrock (University of Regensburg)

186 Further properties of Minimally Doubled Fermions

Minimally doubled fermions reconcile standard chiral symmetry with a minimal number of flavours in accordance with the restrictions of the Nielsen-Ninomiya no-go theorem. Hypercubic symmetry however, is necessarily broken by the alignment of two poles of the propagator in momentum space. The specified direction of the symmetry breaking strongly affects the properties of these actions. We introduce a constant vector \Lambda breaking hypercubic symmetry explicitly, which points from one zero mode to the other and yields a uniform description of the renormalization properties of minimally doubled fermions. We use this vector to clarify the symmetry of the two zero modes.

Speaker: Johannes Weber (University of Tsukuba)

187 Glimpse of $B_K$ on the ultrafine ($a=0.045$ fm) lattices

We report our first experience with the analysis of $B_K$ calculated on the MILC ultrafine lattices using improved staggered fermions. The results are preliminary. However, since it is so close to the continuum, the prematurity does not desecrate the bright splendor of the results much.

Speaker: Taegil Bae (Seoul National University, Seoul, Korea (Republic of))

188 Gluon Mass in Landau Gauge QCD

The interpretation of the Landau gauge lattice gluon propagator as a massive type bosonic propagator is investigated. This is relevant for the analytical studies of the Landau gauge gluon propagator, since in Lattice QCD we are able to also compute the non-pertubative infrared gluon mass and compute how it matches with the ultraviolet region addressed in pertubative QCD. Our analysis suggests a running gluon mass, decreasing with the momentum, starting from a value of $\sim 630$ MeV in the infrared region and suggesting a simple $q^2 \ln q^2$ dependence for momenta above 1 GeV. Our data and our best fit are also compatible with the perturbative behaviour in the right momentum region.

Speaker: Bicudo Pedro (Instituto Superior Técnico, Lisboa)

189 Hadron Form Factors at Large Transfer Momentum (II)

We report a recent breakthrough in lattice QCD calculations of hadron form factors at large momentum transfer. Conventional lattice form-factor calculations typically reach about 2.5 GeV$^2$ or less, but in this work the transfer momentum is pushed as high as 6 GeV$^2$. Our approach can be applied to isotropic lattices and lattices with smaller lattice spacing to calculate even larger-$Q2$ form factors. We will discuss the methodology and demonstrate results for the nucleon and pion from 2+1-flavor anisotropic clover lattices. These measurements could give important theoretical input to experiments, such as those of JLab's 12-GeV program, and provide insight into hadronic structure.

Speaker: Huey-Wen Lin (University of Washington)

190 Improved automated lattice perturbation theory in background field gauge

We present an algorithm to automatically derive Feynman rules for lattice perturbation theory in background field gauge. Vertices with an arbitrary number of both background and quantum legs can be derived automatically from both gluonic and fermionic actions. The algorithm is a generalisation of our earlier algorithm based on prior work by L\"uscher and Weisz. We also present techniques allowing for the parallelisation of the evaluation of the often rather complex lattice Feynman rules that should allow for efficient implementation on GPUs, but also give a significant speed-up when calculating the derivatives of Feynman diagrams with respect to external momenta.

Speaker: Georg von Hippel (Institut f. Kernphysik, Uni Mainz)

191 Improved Semileptonic Form Factor Calculations in Lattice QCD

We investigate two alternatives to the Sequential Propagator Method used in Lattice QCD calculations of heavy-light semileptonic form factors.  In the first method, which we refer to as the Stochastic Propagator Method, we replace the sequential propagator with a stochastic all-to-all propagator.  In the second method, we employ the so called "one-end trick".  After minimizing the stochastic noise we compare the three methods using two N_f=2 ensembles with non-perturbatively O(a) improved Wilson fermions.  The Stochastic Propagator Method results in the most efficient approach for any realistic calculation.  We present O(a) improved, matched lattice results on a single ensemble using this approach. In a complementary effort, we present preliminary O(a) improved, matched results for f_D and f_Ds on three ensembles with the same action as those above.  Standard point-to-all propagators are used. We perform a chiral extrapolation for f_D and f_Ds with sea pion masses as low as ~170 MeV.

Speaker: Richard Evans (Universitaet Regensburg)

192 Improving many flavor QCD simulation using multiple GPU's

The Large Hadron Collider (LHC) experiment has begun to trap the tail of Higgs boson and to find the evidence of a theory beyoned the standerd model (SM). Motivated from the unnatural feature of elementary scalar Higgs field, many models beyond the SM have been proposed and studied. The technicolor (TC) model is one of them and describes the origin of electroweak symmetry breaking without introducing elementary scalar particles. The TC is a scaled-up version of QCD, but should have different fetures from the simple scaled-up QCD. The most promissing TC models should have a slowly running (=walking) coupling and a large mass anomalous dimension. The non-perturavative feature of such models has been investigated using lattice technique over the last years. Especially the gauge theories with many fermions, which realizes the walking feature, are very attractive. Simulating lattice gauge theory with many dynamical fermions is, however, a heavier task than that for QCD, since the computational cost is roughly proportional to the number of dynamical fermions. Improving the simulation algorithm with many dynamical flavors becomes more important. In this poster we show the performance improvements on the HMC algorithm using multiple GPU's suitable to the many flavor simulations. We also present the preliminary results on the runnning coupling constant and the mass anomalous dimension for the $SU(3)$ gauge theory with ten dynamical fermions (ten-flavor QCD) using the Schroedinger functional method.

Speaker: Kenichi Ishikawa (Hiroshima University, Department of Physical Science)

193 K -> pi pi matrix elements from 2+1 flavor lattice QCD

We present a new method for determining K->pipi matrix elements from lattice simulations. This method is less costly than direct simulations of K->pipi at physical kinematics, and evades the Maiani-Testa no-go theorem by simulating with both pions at rest. It improves, however, upon the traditional "indirect" approach of constructing the K->pi pi matrix elements using NLO SU(3) ChPT, which can lead to large higher-order chiral corrections. We illustrate the method with the explicit example of the Delta I =3/2 (27,1) operator, and use the result to obtain a value for Re(A_2). All of our simulations use domain-wall valence quarks on the MILC asqtad-improved gauge configurations. This method, however, can be applied to data computed with any fermion formulation.

Speaker: John Laiho (University of Glasgow)

194 Kaon and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

We discuss the computation of the K and D meson masses in the N_f = 2+1+1 twisted mass lattice QCD setup, where explicit heavy flavour and parity breaking occurs at finite lattice spacing. We present three methods suitable in this context, and verify their consistency.

Speaker: Elisabetta Pallante (University of Groningen)

195 Lattice SU(2) on GPU's

We discuss the CUDA approach to the simulation of pure gauge Lattice SU(2). CUDA is a hardware and software architecture developed by Nvidia for computing on the GPU. We present an analysis and performance comparison between the GPU and CPU with single precision. Analysis with single and multiple GPU's, using CUDA and OPENMP, are also presented. In order to obtain a high performance, the code must be optimized for the GPU architecture, i.e., an implementation that exploits the memory hierarchy of the CUDA programming model. Using GPU texture memory and minimizing the data transfers between CPU and GPU, we achieve a speedup of 200x using 2 NVIDIA 295 GTX GPU's relative to a serial CPU, which demonstrates that GPU's can serve as an efficient platform for scientific computing. With multi-GPU's we are able, in one day computation, to generate 1,000,000 gauge configurations in a 48^4 lattice with beta=6.0 and calculate the mean average plaquette. We present results for the mean average plaquette in several lattice sizes for different beta. Finally we present results for the mean average Polyakov loop at finite temperature.

Speaker: Pedro Bicudo (Instituto Superior Técnico, Lisboa)

196 Minimal doubling and point splitting

Minimally doubled chiral fermions have the unusual property of a single local field creating two fermionic species. Spreading the field over nearby neighbors allows construction of combinations that isolate specific modes. Combining these fields into bilinears produces meson fields of specific quantum numbers.

Speaker: Michael Creutz (Brookhaven Lab)

197 Non-perturbative improvement of SU(2) gauge theory with fundamental or adjoint representation fermions

The research of strongly coupled beyond-the-standard-model theories has generated significant interest in non-abelian gauge field theories with different number of fermions in different representations. Motivated by technicolor scenarios, we study the non-perturbative improvement of the Wilson-clover action using SU(2) gauge fields and fermions in fundamental and adjoint representations. The Sheikholeslami-Wohlert coefficients are fixed using Schrödinger functional simulations.

Speakers: Anne-Mari Mykkänen (University of Helsinki and Helsinki Institute of Physics), Jarno Rantaharju (University of Helsinki and Helsinki Institute of Physics)

198 Octet baryon sigma terms and Baryon ChPT

A status report is given for a joint project between the Budapest-Marseille-Wuppertal collaboration and the Regensburg group to study the quark mass-dependence of octet baryons in SU(3) Baryon ChPT. This formulation is expected to extend to larger masses than Heavy-Baryon ChPT. Its applicability will be tested with 2+1 flavor data which cover three lattice spacings and pion masses down to about 190 MeV, in large volumes. Its use for the determination of octet baryon sigma terms will be discussed.

Speaker: Stephan Durr (Wuppertal University and Julich Supercomputing Center)

199 One flavour QCD

The investigated theory has one Wilson fermion in the fundamental representation with colour gauge group SU(3). In addition to studying the one flavour theory particle spectrum, we test by Monte-Carlo simulations the existence of a CP-symmetry breaking phase and predictions from the orientifold planar equivalence. The poster also describes the computation of the Wilson-Dirac operator determinant sign.

Speaker: Jair Wuilloud (uni Bern)

200 Phase diagram of the G2 gauge higgs model

G2 is the smallest simple and simply connected lie group with a trivial center. Therefore investigations of G2 gauge theories may help to clarify the relevance of center symmetry for confinement. Beside this it has an intriguing connection to SU(3) gauge theorie and to QCD. If one couples a scalar field in the fundamental representation to the gauge field one can break the G2 gauge symmetry to SU(3) gauge symmetry. 6 of the 14 gluons of G2 get a mass while 8 gluons stay massless. These 6 gluons transform with respect to their color degrees of freedom as ordinary quarks and antiquarks in QCD. We will show the full phase diagram of the G2 gauge higgs model obtained with monte carlo simulations and discuss the order of different phase transitions.

Speaker: Björn Wellegehausen (TPI, University Jena)

201 QCD Phase Structure and Imaginary Endpoints

We consider the endpoint of the Roberge-Weiss first order transition line, which is present for imaginary values of the baryon chemical potential, and study its nature in two flavor QCD as a function of the quark masses. We present evidence that the endpoint is first order (hence a triple point) for low quark masses, discuss the fate of the further first order lines departing from it, and explore the consequences which may be relevant to the structure of the QCD phase diagram.

Speaker: Massimo D'Elia (Universita` di Genova & INFN)

202 Rho meson at finite temperature from unquenched lattice QCD

We present results of rho meson mass in lattice QCD with two degenerate flavours of dynamical quarks at finite temperature. Our preliminary results show that the ground state mass remains almost unchanged as the temperature is approaching to the critical temperature from the below. Above T_{c}, we find indication that mesonic excitations survive both at finite quark mass and in the physical limit.

Speaker: Mushtaq Loan (International School, Jinan University)

203 Scaling behavior of chiral phase transition in two-flavor QCD with improved Wilson quarks at finite density

We study scaling behavior of a chiral order parameter defined by an axial Ward-Takahashi identity in two-flavor QCD. It has been shown that the scaling behavior of the chiral order parameter agrees with the scaling function of the three-dimensional O(4) spin model by a simulation with the RG (Iwasaki) improved gauge action and clover improved quark action at zero chemical potential. We extend the scaling study to finite density QCD. Calculating derivatives of the chiral order parameter with respect to the chemical potential in two-flavor QCD with the improved Wilson quarks, we discuss the scaling property of chiral phase transition in the low density region.

Speaker: Shinji Ejiri (Niigata University)

204 Shape of the proton in a uniform magnetic field

The effect of a uniform background magnetic field on the wave function of the d-quark in the ground state of the proton is calculated in Lattice QCD. We focus on the wave functions in the Landau and Coulomb gauges. When the quarks are annihilated at different lattice sites, we observe the formation of a scalar u-d diquark pair within the proton in the Landau gauge, which is not present in the Coulomb gauge. The overall distortion of the wave function under a very large magnetic field, as demanded by the quantisation conditions on the field, is quite small.

Speaker: Waseem Kamleh (University of Adelaide)

205 Staggered fermions simulations on GPUs

We will show our implementation of the RHMC algorithm for staggered fermions on Graphics Processing Units using the NVIDIA CUDA programming language. While previous studies exclusively deal with the Dirac matrix inversion problem, our code performs the complete MD trajectory on the GPU. After pointing out the main bottlenecks and how to circumvent them, we discuss the performance of our code.

Speaker: Claudio Bonati (PI)

206 SU(2) analysis of $B_K$ with staggered fermions

We report a recent progress in determining $B_K$ based on the SU(2) analysis of the data. We use HYP staggered fermions as valence quarks and use asqtad staggered fermions as sea quarks. A number of systematic errors are reviewed in some details.

Speaker: Boram Yoon (Seoul National University)

207 SU(3) Analysis of $B_K$ using staggered fermions

We report a recent progress in the SU(3) analysis of $B_K$ calculated using improved staggered fermions in a mixed action environment: valence quarks are HYP staggered fermions and sea quarks are asqtad staggered fermions. The systematic errors reviewed in some details.

Speaker: Jangho Kim (Department of Physics and Astronomy, Seoul National University)

208 Systemtic Uncertainties in $B_K$ calculated using staggered fermions

We discuss about the systematic errors in $B_K$ calculated on the MILC lattices using improved staggered fermions. We address unresolved issues on the finite volume effect, dependence of $B_K$ on the light sea quark masses, dependence of $B_K$ on the strange sea quark mass, and so on.

Speaker: Yong-Chull Jang (Department of Physics and Astronomy, Seoul National University)

209 The b Quark Mass from Lattice Nonrelativistic QCD

We present a calculation of the b quark mass from lattice NonRelativistic QCD (NRQCD). The b quark mass is extracted using the two-loop NRQCD heavy quark energy shift and mass renormalisation, previously calculated to only one-loop. These parameters are obtained with a hybrid technique: gluonic contributions are extrapolated from a quenched high-beta simulation and the fermionic contributions calculated using automated lattice perturbation theory.

Speaker: Monahan Chris (University of Cambridge)

210 The continuum limit of hadronic correlation functions in the deconfined phase of an SU(3) gauge theory

We explore properties of hadronic excitations at high temperature in the chiral limit by investigating hadron correlation functions in the deconfined phase of quenched QCD. This is achieved by performing a systematic analysis of the influence of cut-off effects on light quark meson correlators at $T=1.5 T_c$ using clover improved Wilson fermions on quenched gauge field configurations.\\ The correlation functions are calculated at four values of the lattice cut-off, i.e. on lattices of size $128^3\times N_\tau$ with $N_\tau = 16,\ 24,\ 32$ and $48$. Whereby we check that finite volume effects are small compared to the significant cut-off dependence observed in the correlation functions. The continuum extrapolation of these correlators are seen to be well under control for distances $0.2 \le \tau T \le 0.5$.\\ We discuss consequences for the determination of hadronic spectral functions and the analysis of their low energy structure.

Speaker: Anthony Francis (Universitaet Bielefeld)

211 The QCD Phase Transition in a Strong Magnetic Background

We investigate the properties of the deconfining/chiral restoring transition for two flavor QCD in presence of a uniform background magnetic field. We adopt a standard staggered discretization of the fermion action, different values of the bare quark mass corresponding to pion masses ranging from 200 to 500 MeV, and magnetic fields up to eB = 1 GeV^2. We present first results regarding the dependence of the deconfinement and chiral transition temperature and strength on the magnetic field.

Speaker: Massimo D'Elia (Universita` di Genova & INFN)

212 The sphaleron rate in the electroweak crossover

The baryon number in the Standard Model is violated by non-perturbative sphaleron transitions. At temperatures above the electroweak scale, the rate of the sphaleron transitions is unsuppressed and has been accurately measured using effective theories on the lattice. At temperatures substantially below the electroweak scale, the Higgs field expectation value is large and the sphaleron rate is strongly suppressed. Here analytical estimates are sufficient. The sphaleron rate, however, has not been calculated in the intermediate temperature range with physical Standard Model parameters. In this work we use an effective electroweak theory on the lattice with multicanonical and real-time simulation methods to calculate the sphaleron rate through the electroweak crossover at Higgs masses of 115 GeV and 160 GeV. The results are significant e.g. for leptogenesis scenarios.

Speaker: Michela D'Onofrio (University of Helsinki)

213 Toward a well defined monopole creation operato

The numerical implementation of monopole creation operator was pointed out to have problems related to bulk transitions that could possibly affect the interpretation of its mean value as an order parameter for monopole condensation. Preliminary evicence is presented that these unexpected behaviours are in fact only due to lattice artefacts and do not overcome the physical intarpretation of the monopole operator.

Speaker: Claudio Bonati (PI)

214 Transport coefficients of causal dissipative relativistic hydrodynamics in quenched lattice simulations

The viscous coefficients are input of the calculation of the relativistic dissipative hydrodynamics and should be given by a microscopic theory. It is known that the coefficients will be calculated by the Green-Kubo-Nakano (GKN) formula if the fluid is described by the relativistic Navier-Stokes (RNS) equation. However, we cannot apply the RNS theory because this theory is acausal and unstable. To avoid these difficulties, we have to consider the effect of retardation by introducing the relaxation time. Theories of this type are called causal dissipative relativistic fluid dynamics (CDRF). Thus, to implement numerical simulations of CDRF, we have to give not only shear and bulk viscosities but also the relaxation times. Recently, a new microscopic formula to calculate the transport coefficients of CDRF from time-correlation functions was proposed [1]. This formula is the analogue of the GKN formula in Navier-Stokes fluids. In this work, we study the transport coefficients of CDFR using the new formula in lattice simulations of SU(3) gauge theory. The simulations are performed on 24^3x4--8 lattices with bare coupling \beta = 6.0, which corresponds to the temperature range of 260--520 MeV. We will discuss temperature dependence of the transport coefficients. [1] T. Koide, E. Nakano and T. Kodama, PRL103, 052301 (2009); G. S. Denicol, X. G. Huang, T. Koide and D.H.Rischke, arXiv:1003.0780.

Speaker: Yu Maezawa (RIKEN)

215 Unquenching the Landau Gauge Lattice Propagators and the Gribov Problem

The gluon and ghost propagators are computed using both quenched and dynamical configurations for the same lattice spacings. The Wilson fermions are simulated at several quark masses. Furthermore, the effect of the Gribov copies is evaluated for all sets of configurations.

Speaker: Paulo Silva (Center for Computational Physics, University of Coimbra)

216 Update on disconnected contributions to hadronic structure.

We report on an ongoing project to calculate disconnected contributions to hadronic structure with results on QCDSF dynamical $n_f=2$ configurations at three volumes.

Speaker: Sara Collins (University of Regensburg)

Wednesday, 16 June

Session 3

217 Computational biology

Speaker: Eytan Domany

Slides domany.pdf

218 LHC results

Speaker: Slawek Tkaczyk

Slides tkaczyk.pdf

10:00 Coffee break

Session 4

219 Lattice quantum gravity

Speaker: Renate Loll

Slides loll.pdf

220 Exact Lattice Susy and AdS/CFT

Speaker: Simon Catterall

Slides catterall.pdf

Lunch and other activities

Excursion

Thursday, 17 June

Session 5

221 Finite temperature QCD

Speaker: Kazuyuki Kanaya

Slides kanaya.pdf

222 The conformal window on the lattice

Speaker: Luigi Del Debbio

Slides deldebbio.pdf

10:00 Coffee break

Session 6

223 QCD at finite density

Speaker: Sourendu Gupta

Slides gupta.pdf

224 Calculation of helium nuclei in quenched lattice QCD

Speaker: Takeshi Yamazaki

Slides yamazaki.pdf

11:30 Lunch and other activities

Parallel 37: Hadronic structure and interactions

225 Forces between static-light mesons

I report about a computation of the isospin, spin and parity dependent potential between a pair of static-light mesons using Wilson twisted mass lattice QCD with two flavors of degenerate dynamical quarks. From the results a simple rule can be deduced stating, which isospin, spin and parity combinations correspond to attractive and which to repulsive forces.

Speaker: Marc Wagner (Humboldt University Berlin)

Slides wagner.pdf

226 Static-light meson potentials

We investigate potentials between pairs of static-light mesons in n_f=2 Lattice QCD, in different spin and isospin channels. The question of attraction and repulsion is particularly interesting with respect to the X(3872) charmonium state and charged candidates such as the Z+(4430). The simulations are performed on QCDSF Sheikholeslami-Wohlert gauge configurations with lattice spacings 0.08 - 0.1 fm.

Speaker: Martin Hetzenegger (University of Regensburg)

Slides martin_hetzenegger_lattice2010.pdf

227 The qbar - q potential from Bethe - Salpeter amplitudes on lattice

The hadron spectroscopy for mesons including heavy quarks has been continuously studied. Various models with the use of non-relativistic framework for QCD (NRQCD) are applied to the studies of the heavy quark bound systems. The potentials between anti-quarks and quarks are the most important ingredients in models from NRQCD. So far, the static `Qbar-Q' potential with relativistic corrections have been studied using Wilson loop in lattice QCD. The static potential reveals that the Qbar-Q potential contains confinement and Coulomb potentials, where the finite mass effects have been included through perturbative expansion in 1/m_Q. In this study, we investigate the `qbar-q' potentials with finite quark masses in quenched lattice QCD simulation. In order to derive the qbar-q potentials, we have utilized the method which has been recently developed by HAL QCD collaboration. In this method, we measure the Bethe-Salpeter amplitudes in qbar-q system, and the potentials are derived from the amplitudes through the effective Schroedinger equation. We present our results of qbar-q potentials in J^{P}=0^-,1^- channel.

Speaker: Yoichi Ikeda (RIKEN, Nishina Center)

Slides ikeda.pdf

228 Nucleon and N*(1535) Distribution Amplitudes

The QCDSF collaboration has investigated the distribution amplitudes and wave function normalization constants of the nucleon and its parity partner, the N*(1535). In this talk, I will report on recent progress in the calculation of these quantities. The calculations have been performed on configurations with two dynamical flavors of O(a)-improved Wilson fermions. New data at pion masses of approximately 270 MeV helps in significantly reducing errors in the extrapolation to the physical point.

Speaker: Rainer Schiel (University of Regensburg, Germany)

Slides Schiel_NNstarDAs.pdf

229 Spatial diquark correlations in a hadron

Using lattice QCD, a diquark can be studied in a gauge-invariant manner by binding it to a static quark in a heavy-light-light hadron. We compute the simultaneous two-quark density of a diquark, including corrections for periodic boundary conditions. We define a correlation function to isolate the intrinsic correlations of the diquark and reduce the effects caused by the presence of the static quark. Away from the immediate vicinity of the static quark, the diquark has a consistent shape, with much stronger correlations seen in the good (scalar) diquark than in the bad (vector) diquark. We present results for pion mass 293 MeV in unquenched QCD and for pion mass 893 MeV in quenched QCD, and discuss the dependence of the spatial size on the pion mass.

Speaker: Jeremy Green (Center for Theoretical Physics, Massachusetts Institute of Technology)

Slides green-diquark.pdf

Parallel 39: Nonzero temperature and density

230 A study of the complex action problem in a simple model for dynamical compactification in superstring theory using the factorization method.

Monte Carlo simulations of matrix models could play an important role in understanding string theories in a similar fashion that lattice QCD has contributed to the understanding of the non-perturbative regime of quantum field theories. The IKKT or IIB matrix model has been proposed as a non--perturbative definition of superstring theory. The model provides a mechanism for the dynamical generation of spacetime, which suggests that also the dimensionality of spacetime can arise dynamically by breaking the SO(10) rotational invariance of the model in the 10-dimensional defining space. We study the complex action problem in a matrix model which has been proposed as a toy model for the study of the dynamical compactification of spacetime dimensions scenario of the IIB matrix model of superstrings. The complex action problem in Monte Carlo simulations of the model turns out to be quite severe and we use the factorization method proposed in hep-th/0108041 for its study. We compute the density of states of the order parameter in the phase quenched model and the corresponding phase factor. Then the large N extrapolation is performed by using their nice scaling properties. The asymptotic behavior is understood by using simple theoretical arguments which enable us to study the important region of configuration space which is heavily suppressed by the fluctuations of the phase. We conclude that the SO(4) rotational symmetry of the four dimensional model is dynamically broken in accordance with the predictions of calculations performed using the gaussian expansion method.

Speaker: Konstantinos Anagnostopoulos (National Technical University of Athens)

Slides Anagnostopoulos.pdf

231 How the Quark Number fluctuates in QCD at small chemical potential

We discuss the distribution of the quark number over the gauge fields for QCD at nonzero quark chemical potential. As the quark number operator is non-hermitian, the distribution is over the complex plane. Moreover, because of the fermion determinant, the distribution is not real and positive. The computation is carried out within leading order chiral perturbation theory and gives direct insight into the delicate cancellations that take place in contributions to the total baryon number.

Speaker: Kim Splittorff (The Niels Bohr Institute)

Slides splittorff.pdf

232 Poisson statistics in the high temperature QCD Dirac spectrum

In the epsilon regime of QCD the low-end of the Dirac spectrum is described by random matrix theory. In contrast, there has been no similarly well established staistical description in the high temperature, chirally symmetric phase. Using lattice simulations I show that at high temperature a band of extremely localized eigenmodes appear at the low-end of the Dirac spectrum. The corresponding eigenvalues are statistically independent and obey a generalized Poisson distribution. Higher up in the spectrum the Poisson distribution rapidly crosses over into the bulk distribution predicted by the random matrix ensemble with the corresponding symmetry. My results are based on quenched lattice simulations with the overlap and the staggered Dirac operator done well above the critical temperature at several volumes and values of N_t. I also discuss the crucial role played by the fermionic boundary condition and the Polyakov-loop in this phenomenon.

Speaker: Tamas Kovacs (University of Pecs)

Slides kovacs.pdf

233 Exact results for two-color QCD at low and high density

We consider the chiral extension of the real Ginibre ensemble of random matrices with dynamical flavors to study the spectrum of the Dirac operator in two-color QCD with nonzero baryon chemical potential. We show that at maximum non-Hermiticity the random-matrix model is equivalent to the low-energy effective theory at high density in the epsilon regime. We obtain the microscopic spectral density of the Dirac eigenvalues in the limits of both strong and weak non-Hermiticity for a general number of flavors. We illustrate the main characteristics of the spectrum and comment on the sign problem for non-degenerate quark masses. Our results can in principle be checked by lattice QCD simulations.

Speaker: Tilo Wettig (University of Regensburg)

Slides wettig.pdf

234 QCD at finite chemical potential in the nilpotency expansion

The nilpotency expansion is an approach to field theories based on time-dependent Bogoliubov transformations. When the theories are regularized on a lattice we perform independent Bogoliubov transformations at each time slice. The time-dependent parameters of the transformations can naturally be interpreted as bosonic fields associated to bosonic composites of fermions. They are caracterized by an index of nilpotency, which is the number of fermionic states in their structure functions.The original action is explicitly transformed in an exactly equivalent action expressed in terms of bosonic fields and fermionic fields with the quark quantum numbers (quasiparticles). By making the parameters of the Bogoliubov transformations time-dependent we can conserve term by term several symmetries, in particular gauge invariance. We can then safely perform different approximations. We construct a perturbative approach assuming the index of nilpotency as an asymptotic parameter and performing an asymptotic expansion in its inverse, the nilpotency expansion. We have studied QCD in the saddle point approximation. We propose a new procedure to investigate the case of finite chemical potential. If we perform also an expansion in the gauge coupling constant we get results compatible with the standard ones.

Speaker: Fabrizio Palumbo (LNF)

Slides palumbo.pdf

Parallel 41: Algorithms and machines

235 Multigrid solver for clover fermions

I will present an adaptive multigrid Dirac solver developed for Wilson clover fermions which offers order-of-magnitude reductions in solution time compared to conventional Krylov solvers. The solver incorporates even-odd preconditioning and mixed precision to solve the Dirac equation to double precision accuracy and shows only a mild increase in time to solution for decreasing quark mass. I will show actual time to solution on production lattices in comparison to conventional Krylov solvers and will also discuss the setup process and its relative cost to the total solution time.

Speaker: James Osborn (Argonne National Lab)

Slides osborn.pdf

236 A mass preconditioning for lattice Dirac operators

In the solution of the lattice Dirac equation with heavy quarks masses the numerical precision obtained at large time distances from the source may be significantly smaller with respect to the precision obtained at small times. This happens for each gauge configuration because typical algorithms used to perform numerical inversions require that a "global" residue is smaller than a certain value while, because of the heavy quark mass, the time-slices at large distances from the source give a negligible contribution to this residue. In such cases we propose to precondition the lattice Dirac operator by multiplying the quark field at different time-slices with a user tunable function alpha(x0) and by modifying accordingly the boundary conditions in the time direction. With a properly chosen function one can improve significantly the numerical precision of heavy quark propagators at large time distances or, by changing the function, accelerate the inversion of lattice Dirac operators with light quark masses.

Speaker: Nazario Tantalo (INFN sez. Roma "Tor Vergata")

Slides tantalo_lattice10.pdf

237 Disconnected Diagrams: Progress, Methods and Prospects

Computation of disconnected or non-valence quark loops presents a computationally challenging problem. Absent these contributions operators with zero flavor quantum numbers can not be studied. This is a report on progress to measure the strange quark contributions to nucleon form factors. The increasing importance of GPU architectures and multigrid methods will be discussed, as will prospects for increased accuracy as these methods are further exploited.

Speaker: Richard C. Brower (Boston University)

Slides brower_lat10.pdf

238 Exact Calculation of Disconnected Loops

The exact computation of the disconnected diagram contribution to a number of hadronic observables, such as the eta prime mass and the nucleon isoscalar form factors, is considered to explicitly expose the gauge noise associated with these diagrams. A Wilson action on lattices of SU(3) SESAM gauge field configurations with two dynamical flavors and a volume of 16^3X32 are utilized. An exact inversion method is employed to perform O(10^6) inversions of the Wilson-Dirac matrix per configuration. To accelerate computations, GPGPU technology is exploited by utilizing conjugate gradient solvers on the NVIDIA CUDA platform. A modified interface to QUDA library is employed which provides mixed precision implementations of both CG and BiCGstab algorithms. In particular, it allows one to achieve a performance level in excess of 100 Gflop/s with respect to NVIDIA GT200 micro-architecture.

Speaker: Alan O'Cais (Cyprus Institute)

Slides ocais.pdf

239 Autocorrelations in Hybrid Monte Carlo Simulations

Simulations of QCD suffer from severe critical slowing down towards the continuum limit. This problem is known to be prominent in the topological charge, however, all observables are affected to various degree by these slow modes in the Monte Carlo evolution. We investigate the slowing down in high statistics quenched and dynamical fermion simulations and propose a new error analysis method, which gives a realistic estimate of the contribution of the slow modes to the errors.

Speaker: Francesco Virotta (NIC, DESY Zeuthen)

Slides virotta.pdf

Parallel 43: Applications beyond QCD

240 Condensate enhancement for mass generation in SU(3) gauge theory.

Models of electroweak symmetry breaking that use new strong interactions may depend on an enhanced chiral condensate in order to be able to generate the known fermion masses. This may be the case for near conformal gauge theories. Here I present preliminary results of the Lattice Strong Dynamics collaboration for the chiral condensate in SU(3) gauge theory with two six and ten DWF flavors in the fundamental representation.

Speaker: Pavlos Vranas (Lawrence Livermore National Laboratory)

Slides vranas.pdf vranas_session_43_lat10.ppt

241 Flavor dependence of hadron spectrum in Technicolor theories

An alternative to the Standard Model Higgs mechanism to explain the generation of the W and Z boson masses is to have dynamical electroweak symmetry breaking as a result of some new strong interactions at high energies. Lattice studies of strongly-interacting theories other than QCD can give us important information about the behaviors of such Technicolor theories in a non-perturbative framework. In this talk we present a study of the light hadron spectrum in the SU(3) gauge theory with $N_f = 2$ and 6 flavors of domain wall fermions in the fundamental representation. In particular, we study the chiral behaviors of the pseudoscalar, vector and axial vector mesons, and test the Weinberg's spectral sum rules under the assumption of vector-pole dominance. Preliminary results with $N_f = 10$ will also be presented.

Speaker: George Fleming (Yale University)

Slides fleming.pdf

242 Flavor dependence of the S parameter in SU(3) gauge theory

Precision electroweak observables such as the Peskin--Takeuchi S parameter have long been used to constrain models of electroweak symmetry breaking that involve new strong dynamics. However, nonperturbative calculations of S from first principles have previously only been performed for QCD. I present initial results by the Lattice Strong Dynamics (LSD) Collaboration for the S parameter in SU(3) gauge theory with 2 and 6 flavors of fermions in the fundamental representation.

Speaker: David Schaich (Boston University)

Slides schaich.pdf

243 Improved Lattice Spectroscopy of Minimal Walking Technicolor

Lattice studies of theories other than QCD have recently begun to shed light on the conjectured conformal window of Yang-Mills field theories, and whether they can help to form viable models of dynamical electroweak symmetry breaking. Minimal Walking Technicolor has attracted particular attention. We describe recent spectroscopic studies of MWT, searching for signs of near-conformal behaviour and efforts to analyse the systematic difficulties encountered in these studies.

Speaker: Eoin Kerrane (School of Physics and Astronomy, University of Edinburgh)

Slides kerrane.pdf

244 Chiral symmetry of graphene and strong coupling lattice gauge theory

Electrons on suspended graphene (monoatomic layer of carbon atoms) can be described as (2+1)-dimensional massless Dirac fermions strongly interacting with (3+1)-dimensional compact or non-compact U(1) gauge field. By employing the techniques of square lattice regularization and strong coupling expansion, we find that the electrons obtain a finite spectral gap in the strong coupling regime do to spontaneous breaking of global chiral symmetry. The magnitude of the gap is analytically calculated up to the next-to-leading order in the strong coupling expansion. We have also derived a mass formula for the pseudo Nambu--Goldstone boson excitation associated to the symmetry breaking, which is analogous to the Gell-Mann--Oakes--Renner relation for pions in QCD.

Speaker: Yasufumi Araki (University of Tokyo)

Slides araki.pdf

Parallel 45: Hadron spectroscopy

245 Electromagnetic splittings of charged and neutral mesons from improved staggered quarks

We extend MILC's initial study of the electromagnetic splittings of charged and neutral mesons, and the violation of Dashen’s theorem. Meson masses are calculated using the MILC Nf = 2 + 1, staggered SU(3) gauge configurations, and independently generated U(1) gauge configurations. The meson correlators are calculated using SU(3)xU(1) gauge fields. A large fraction of the meson correlators are calculated using an implementation of the MILC staggered multi-mass inverter that runs on a single NVIDIA GPU in double precision. When the current analysis is complete, we will have results at three lattice spacings, from about 0.15 to 0.09 fm, with several light quark masses at each lattice spacing. Once electromagnetic effects are included in the corresponding rooted, staggered chiral perturbation theory calculations, we should have excellent control over the chiral and continuum limits.

Speaker: Aaron Torok (Indiana U.)

Slides torok.pdf

246 Isopin breaking study on lattice

We investigate isopin breaking effects due to different masses and electric charges between up and down quarks non-perturbatively using lattice QCD+QED with domain wall quarks. Individual up, down, and strange quark masses are determined using $K^\pm, K^0,$ and $\pi^\pm$ meson masses as inputs. New challenges include calculations for the electromagnetic (EM) correction to the decay constants, introduction of the electric charge effect of sea quarks (full QCD+ full QED), and the disconnected loop diagram in the $\pi^0$ propagator. We employ QCD gauge emsembles using 2+1 flavors of domain wall fermions and the Iwasaki gauge action. These configurations have been generated by RBC and UKQCD collaborations.

Speaker: Taku Izubuchi (Brookhaven National Laboratory & RIKEN-BNL Research Center)

Slides Izubuchi.pdf

247 Electromagnetic corrections to light hadron masses

At the precision reached in current lattice QCD calculations, electromagnetic effects are becoming numerically relevant. We will present preliminary results for electromagnetic corrections to light hadron masses, based on simulations in which a U(1) degree of freedom is superimposed on N_f=2+1 QCD configurations.

Speaker: Antonin Portelli (Centre de Physique Théorique de Marseille (France))

Slides portelli.pdf

248 D_s meson spectroscopy

Preliminary results are presented for the spectrum of D_s mesons using the 2+1 flavor Clover-Wilson configurations made available by the PACS-CS collaboration. For the heavy quark, the Fermilab method is employed and we report on the tuning of the charm-quark hopping parameter. As our main focus, we present initial results for the spectrum of P-wave states, where previous results have been mostly from quenched calculations. As a cross-check, some calculations of the charmonium spectrum are also carried out.

Speaker: Daniel Mohler (TRIUMF)

Slides mohler.pdf

249 Study of the newly discovered mesons in the charm region with chiral fermions.

We investigate if the newly discovered mesons in the charm region, such as D_s(2317), X(3872), Z^+(4430), are tetraquark mesoniums. With quarks and antiquarks in periodic and antiperiodic boundary conditions respectively in the spatial directions, we try to find out if the ground states from the tetraquark interpolation fields are one meson or two meson states. We use valence overlap fermions on 2+1 flavor domain wall fermion configurations. $Z_4$ grid sources are adopted to increase statistics.

Speaker: Ming Gong (University of Kentucky)

Slides gong.pdf

Parallel 47: Theoretical developments

250 Species doublers as supermultiplet partners in lattice supersymmetry: ---General outlook---

Species doublers of chiral fermions have been considered as unwanted particles. We propose a new formulation where the species doublers play a crucial role as supermultiplet partners of lattice supersymmetry. The basic ideas for the simplest model together with the general philosophy of the formulation and the connection with the link approach will be explicitly explained.

Speaker: Noboru Kawamoto (Hokkaido University)

Slides kawamoto_lattice2010-1.pdf

251 Species doublers as supermultiplet partners in lattice supersymmetry. The supersymmetric quantum mechanics case.

By interpreting species doublers as members of the same supermultiplet we describe the N=2 supersymmetric quantum mechanichs (including interaction) on a lattice with both supersymmetries exactly realized. Supersymmetric Ward identities are satisfies and the continuum limit is smooth. Interaction is non-local on the lattice, but locality is recovered in the continuum limit.

Speaker: Alessandro D'adda (INFN, Sezione di Torino and Dipartimento Fisica Teorica, Università di Torino)

Slides d'adda_lattice2010.ppt

252 Supersymmetry non-renormalization theorem from a computer and the AdS/CFT correspondence

We perform Monte Carlo simulation of the plane-wave matrix model or the BMN matrix model, which has 16 supercharges. The model has many degenerate supersymmetric vacua, and by picking up a particular one, we can obtain 4d N = 4 super Yang-Mills theory on R*S^3 in the planar limit based on the idea of a novel large-N reduction. We study correlation functions of non-extremal operators, and find clear evidence that the supersymmetry non-renormalization theorem is at work for two-point and three-point functions for general backgrounds. This suggests that the theorem actually holds in a wide class of supersymmetric theories other than 4d N = 4 super Yang-Mills theory, in which it was already proven. For four-point functions, we observe small violation of the non-renormalization property, which is consistent with a result obtained from the AdS/CFT correspondence.

Speaker: Masazumi Honda (SOKENDAI,KEK)

Slides Lattice2010_honda.ppt

253 Witten index from lattice simulation

I propose a method for measuring the Witten index using a lattice simulation. The index is useful to discuss spontaneous breaking of supersymmetry. As a test of the method, I also report some numerical results for the supersymmetric quantum mechanics, for which the index is known.

Speaker: Issaku Kanamori (INFN, Torino and Univ. of Turin)

Slides lattice2010kanamori.pdf

254 A study of N=2 Landau-Ginzburg model by lattice simulation based on a Nicolai map

It is conjectured that the two-dimensional N=2 Wess-Zumino model with a quasi-homogeneous superpotential provides a Landau-Ginzburg description of the N=2 superconformal minimal models. For the simplest cubic superpotential W=¥lambda ¥Phi^3 /3, it is expected that the Wess-Zumino model describes A_{2} model and the chiral superfield ¥Phi shows the conformal weight (h,¥bar{h})=(1/6,1/6) at the IR fixed point. We will examine this conjecture by a lattice simulation, extracting the weight from the finite volume scaling of the susceptibility of the scalar component in ¥Phi. We adopt a lattice model with the overlap fermion, which possesses a Nicolai map and a discrete R-symmetry. We set a¥lambda=0.3 and sample scalar configurations by solving the Nicolai map on each L ¥times L lattices, with L=18, 20, 22, 24, 26, 28, 30, 32. To solve the map, we use the Newton-Raphson algorithm with various initial configurations. About 640 configurations are analyzed on each L, and the fermion determinants are explicitly evaluated. The result is 1-h-¥bar{h}=0.660¥pm0.011, which is consistent with the conjecture.

Speaker: Hiroki Kawai (University of Tokyo)

Slides Hiroki_Kawai.pdf

16:10 Coffee break

Parallel 38: Hadronic structure and interactions

255 Two-photon decay of $\pi^0$ from two-flavor lattice QCD

We discuss chiral and momentum extrapolation of the transition form factor of $\pi^0$ to two-photon using one-loop chiral perturbation theory (ChPT). Fitting the lattice data with the ChPT formula obtained for off-shell photons, we estimate low-energy constants that describe mass and momentum dependence of the $\pi^0$ to two-photon decay, which can be used to estimate the physical $\pi^0 -> \gamma \gamma$ amplitude.

Speaker: Eigo Shintani (RIKEN-BNL)

Slides 1_shintani-slide100617.pdf

256 Simulations with dynamical HISQ quarks

We study the lattice spacing dependence of physical quantities in simulations with the HISQ quark action, with four flavors of dynamical quarks. This study uses runs at several lattice spacings, but with the light quark mass held fixed at two tenths of the strange quark mass. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses. We also discuss methods for setting the scale, or assigning a lattice spacing to ensembles run at unphysical parameters. Finally, we discuss plans for further generation of four-flavor lattices using the HISQ action.

Speaker: Doug Toussaint (University of Arizona)

Slides 2_lattice10.pdf

257 Leading order hadronic contribution to g-2 from twisted mass QCD

The hadronic contributions to the anomalous magnetic moment of the muon are an interesting challenge for lattice QCD calculations, especially given a persistent discrepancy between theory and experiment. We have calculated the leading order hadronic contribution for pion masses from 270 MeV to 600 MeV using two flavors of dynamical twisted-mass fermions. We have examined the finite-size dependence with spatial volumes ranging from (1.6 fm)^3 to (2.7 fm)^3 and we have studied lattice artifacts with lattice spacings of 0.086 fm and 0.067 fm.

Speaker: Dru Renner (NIC, DESY)

Slides 3_renner.pdf

258 non-locality of the nucleon-nucleon potential from Lattice QCD

Recently, a new approach to calculate the nuclear potential from　lattice QCD has been proposed. In this approach, the nuclear　potential is constructed from Bethe-Salpeter (BS) wave functons　through the Schroedinger equation. The procedure leads to non-local　but energy independent potential U(r,r'), which can be expressed in terms of local functions by derivative expansion. In several recent applications of this method, local potentials, which　correspond to the leading order (LO) terms of the derivative expansion, are calculated from the BS wave function at E \simeq 0 MeV, where E is the center of mass energy. It is therefore important to estimate the validity of the LO potential and size of contribution from higher order terms, which can be done by examining the energy and angular momentum dependence of the LO potential. In this report, we will estimate the energy dependence of LO potential by comparing two LO potentials obtained at two energies in quenched lattice QCD with m_\pi = 530 MeV. We will also examin the possible L dependence of S=0 (spin singlet) potential, by comparing ^1S_0 and ^1D_2 central potentials. We find that, in each comparison, difference of the LO potentials is negligible within the statistical errors. This implies that the contribution from NLO terms are less significant, so that the LO potential obtained at E \simeq 0 (L \le 2) is valid up to (at least) 45 MeV (L=2) to describe the NN interaction in quenched QCD with m_\pi = 530 MeV.

Speaker: Keiko Murano (High Energy Accelerator Research Organization, KEK)

Slides 4_Lat10.murano.pdf

Parallel 40: Nonzero temperature and density

259 Thermodynamics of $SU(N)$ gauge theories in $2+1$ dimensions in the $T < T_c$ regime.

We present Monte Carlo results for the thermodynamics of pure $SU(N)$ gauge theories ($N=2,...,6$) in $2+1$ dimensions. We focused on the confined phase region ($T < Tc$) and discuss scaling properties with $N$. We also compare our results with a glueballs gas and the bosonic string predictions for the Hagedorn spectrum.

Speaker: Alessandra Feo (Universita' di Torino and INFN Torino)

Slides feo.pdf

260 SU(3) thermodynamics at high temperatures

We determine the SU(3) equation of state and the Polyakov loop up to perturbative temperatures on lattices with nt=5,6 and 8.The continuum results are contrasted to various resummations and orders of perturbation theory. At very low temperatures we explain our data in terms of a glueball gas.

Speaker: Kalman Szabo (Wuppertal U.)

Slides Borsanyi.pdf

261 Coherent center domains in local Polyakov loops

Coherent center domains in local Polyakov loops We analyze properties of local Polyakov loops using quenched as well as dynamical SU(3) gauge configurations for a wide range of temperatures. It is demonstrated that for both, the confined and the deconfined phases, the local Polyakov loop prefers phase values near the center elements $1, e^{pm2\pi/3$. We divide the sites of the lattice into three sectors according to these phases and show that the sectors give rise to the formation of clusters. For a suitable definition of these clusters we find that the deconfinement transition manifests itself as the onset of percolation of the clusters.

Speaker: Julia Danzer (Karl-Franzens University)

Slides Danzer.pdf

262 Continuum Thermodynamics of the SU(N) Gauge Theory

The thermodynamics of the deconfined phase of the SU(N) gauge theory is studied. Careful study is made of the approach to the continuum limit. The latent heat of the deconfinement transition is studied, for the theories with 3, 4 and 6 colors. Continuum estimates of various thermodynamic quantities are studied, and the approach to conformality investigated. The bulk thermodynamic quantities at different N are compared, to investigate the validity of 'tHooft scaling at these values of N.

Speaker: Saumen Datta (Tata Institute of Fundamental Research, Mumbai)

Slides datta.pdf

Parallel 42: Algorithms and machines

263 Rational Domain-Decomposed HMC

Test results for a Hybrid Monte Carlo (HMC) algorithm combined the Domain-Decomposed HMC algorithm and the Rational HMC algorithm are presented.

Speaker: Yoshifumi Nakamura (University of Regensburg)

Slides nakamura.pdf

264 A worm-inspired algorithm for the simulation of Abelian gauge theories

We present an algorithm in which the all-order strong coupling expansion of the Abelian U(1) gauge theory with Wilson plaquette action is sampled . In addition to the vacuum closed surface graphs of the partition function we propose to also allow for a class of defects (boundaries) related to Wilson loops in the ensemble. The efficiency of our scheme in estimating various observables is compared to a standard Metropolis algorithm.

Speaker: Tomasz Korzec (HU Berlin)

Slides korzec.pdf

265 The three-dimensional XY model at finite chemical potential using complex Langevin dynamics

The three-dimensional XY model is studied at finite chemical potential using complex Langevin dynamics. The validity of the approach is probed at small chemical potential using imaginary chemical potential and continuity arguments, and at larger chemical potential by comparison with the world line method. While complex Langevin works for larger beta, we find that it fails for smaller beta, in the region of the phase diagram corresponding to the disordered phase.

Speaker: Frank James (Swansea University)

Slides james.pdf

266 Implementation and performance optimization of Lattice QCD Tool Kit on the Cell/B.E.

We report an implementation and an efficient DMA transfer for SU(3) matrix-matrix and matrix-vector multiplication on Cell/B.E., which is a part of our project, Lattice Tool Kit on the Cell/B.E.. Last year, we reported results on QS20. After that we found the measured execution time is wrong because values on a resistor are distorted at the first measurement. The actual speed of the matrix multiplication on SPEs is 20GFLOPS together with data transfer from main memory by DMA, which is 23% of the theoretical peak speed of this calculation. Performance of our code on the Cell B.E. is limited by the bandwidth between main memory and the Cell SPEs. We discuss the cause of this low value and a possible remedy.

Speaker: Shinji Motoki (Graduate School of BioSphere Science Hiroshima University)

Slides motoki.pdf

Parallel 44: Applications beyond QCD

267 Exploration of the phase structure of the $SU(N_c)$ lattice gauge theory with many Wilson fermions at strong coupling

We explore aspects of the phase structure of $SU(2)$ and $SU(3)$ lattice gauge theories at strong coupling with many flavours $N_f$ of Wilson fermions in the fundamental representation. The pseudoscalar meson mass and the quark mass as a function of hopping parameter are observed to deviate from the expected analytic dependence, at least for sufficiently large $N_f$. Implications of this effect and the phase structure about the existence or non-existence of Aoki phase are discussed, including the relevance to recent searches for the conformal window.

Speaker: Keiichi Nagai (KEK, Theory Center)

Slides nagai.pdf

268 MCRG Minimal Walking Technicolor

We present a Monte Carlo renormalization group study of the SU(2) gauge theory with two Dirac fermions in the adjoint representation. Using the two lattice matching tecnhique recently advocated and exploited by Anna Hasenfratz, we measure the running of the coupling and the anomalous mass dimension.

Speaker: Liam Keegan (Edinburgh University)

Slides keegan.pdf

269 Mass anomalous dimension and running of the coupling in SU(2) with six fundamental fermions

We simulate SU(2) gauge theory with six massless fundamental Dirac fermions. By using the Schrödinger Functional method we measure the running of the coupling and the fermion mass over a wide range of length scales. We observe very slow running of the coupling and construct an estimator for the fermion mass anomalous dimension at an IR fixed point. Our results are consistent with an IRFP coupling of 2.95 < g^2 < 5.60 and a corresponding anomalous dimension of 0.07 < γ < 0.79.

Speaker: Thomas Pickup (University of Oxford)

Slides pickup.pdf

270 Study of the scaling properties in SU(2) gauge theory with eight flavors

We present our preliminary study of the SU(2) gauge theory with 8 flavor of fermions in fundamental representation. This theory could be a candidate of the gauge theory with conformal fixed point. By studying physical observables such as running gauge coupling in twisted boundary conditions, we investigate a possible signal for a conformal behavior.

Speaker: Hiroshi Ohki (Osaka University)

Slides ohki.pdf

Parallel 46: Hadron spectroscopy

271 Charmonium spectroscopy from Nf=2+1 dynamical anisotropic lattices

Preliminary results for the charmonium spectrum are presented. The calculation uses distilled quark propagators measured on the N_f=2+1 dynamical anisotropic lattices of the Hadron Spectrum Collaboration and includes an exploration of disconnected diagrams and decays relevant for threshold effects.

Speaker: Sinead Ryan (Trinity College Dublin)

Slides SRyanLat2010.pdf

272 Update on charm annihilation contribution to the hyperfine splitting in charmonium

We report our final results for the contributions of the disconnected diagrams to the hyperfine splitting in charmonium. Our study includes both the quenched and dynamical cases on ensembles with lattice spacings of approximately 0.06 fm and 0.09 fm. Our new approach tunes the charm quark mass so that the rest mass of the $\eta_c$ is close to its physical value. This method of tuning gives a better accounting of the glueball interactions contributing to the mass shift of the $\eta_c$ and $J/\psi$.

Speaker: Ludmila Levkova (University of Utah)

Slides LLevkova.pdf

273 Bottom meson masses from a RHQ action on a fine 2+1 flavor DWF lattice

We extend our previous relativistic heavy quark (RHQ) charm calculations performed on the $32^3 \times 64$, $1/a=2.32$ GeV RBC/UKQCD lattice ensembles to states including bottom quarks. We calculate masses of bottomium, bottom-strange and bottom-light states, match and compare them to known experimental values. We also compare our results with those determined on the $24^3\times 64, 1/a=1.73GeV$ to assess the RHQ method.

Speaker: Peng Hao (Columbia University, USA)

Slides talk_hao.pdf

274 The spectrum of static-light baryons in twisted mass lattice QCD

We compute the static-light baryon spectrum with N_f = 2 flavors of sea quarks using Wilson twisted mass lattice QCD. As valence quarks we consider unitary light quarks (with a corresponding pion mass of around 340 MeV) as well as partially quenched light quarks, which have the mass of the physical strange quark. We extract masses of states with isospin I = 0, I = 1/2 and I = 1, with light cloud angular momentum j = 0 and j = 1, and with parity P = + and P = -. We present a preliminary extrapolation in the light u/d and in the heavy quark mass to the physical point and compare with available experimental results.

Speaker: Christian Wiese (Humboldt-University Berlin)

Slides wiese_lattice.pdf

Parallel 48: Theoretical developments

275 Search for non-perturbative mechanisms to generate a W boson mass

As long as a Higgs boson is not observed, the design of alternative mechanisms for electroweak symmetry breaking remains of interest. The question addressed here is whether there are possibly non-perturbative mechanisms, which deconfine SU(2) at zero temperature and generate massive vector bosons. Results for a model with a mixing interaction of SU(2) and U(1) gauge fields, which is invariant under unified SU(2)$\otimes$U(1) gauge transformations, are presented.

Speaker: Bernd Berg (Florida State University)

Slides berg_lattice2010.pdf

276 Topological gravity on a lattice

I review the connection between Chern Simons theory and three dimensional Einstein-Hilbert gravity. I point out that both the moduli space and topological observables in the gravitational theory are shared with a twisted super Yang-Mills theory. The latter possesses a lattice formulation which preserves many features of this topological structure. We thus conjecture that the lattice theory provides a non-perturbative regularization for three dimensional quantum gravity - free from the usual problems of path integral approaches to Euclidean quantum gravity.

Speaker: simon catterall (Syracuse University)

Slides catterall_gravlat10.pdf

277 Large-N beta function and static inter-quark potential

We analyze the numerical findings about the lattice static inter-quark potential of the SU(N) Yang-Mills theory in the light of Luscher-Weisz effective action on the string-theory side and of a recently proposed large-N beta function on the field-theory side. On the field-theory side we explain how the large-N beta function is obtained via a certain version of the loop equation of the pure Yang-Mills theory by localization techniques based on homology theory that are dual to the localization of certain BPS Wilson loops of supersymmetric gauge theories based on cohomology theory.

Speaker: Marco Bochicchio (INFN and Scuola Normale Superiore)

Slides bochicchio_lattice2010.pdf

278 From loops to surfaces

The generating function for the characters of the N totally antisymmetric representations of a Wilson-loop matrix in SU(N) gauge theory is the partition function for fermions living on the closed curve making up the loop. This has an obvious generalization. The talk will present results about the case of surface operators

Speaker: Herbert Neuberger (Rutgers)

Slides neuberger_lattice_2010.pdf

Other activities

Social dinner

Friday, 18 June

Session 7

279 Phenomenology from the lattice

Speaker: Christopher Sachrajda (University of Southampton)

Slides sachrajda_lattice2010.pdf

280 Heavy flavors on the lattice

Speaker: Jochen Heitger

Slides slides_heitger.pdf

10:00 Coffee break

Session 8

281 Improving hadron creation operators on the lattice

Speaker: Mike Peardon

Slides Peardon.pdf

282 String effects in the yang-mills theory

Speaker: Michele Pepe

Slides Pepe_Lattice2010.pdf

Lunch and other activities

Parallel 49: Hadronic structure and interactions

283 Charmonium-Nucleon potential from lattice QCD

Low energy charmonium-nucleon interaction is of particular interest in this talk. The heavy quarkonium state such as the charmonium($c\bar{c}$) state does not share the same quark flavor with the nucleon so that $c\bar{c}$-nucleon interaction might be described by the gluonic van der Waals interaction, which is weak but attractive. Therefore, the detail information of $c\bar{c}$-nucleon interaction is vital for considering the possibility of the formation of charmonium bound to nuclei. We will present the results for $c\bar{c}$-nucleon potential from quenched lattice QCD, which is defined from the equal-time Bethe-Salpeter amplitude with local interpolating operator for the charmonium and nucleon. A $c\bar{c}$-nucleon potential is required for precise prediction of the binding energy of nuclear-bound charmonium in exact few body calculations. Through a study of the $\eta_c$-nucleon interaction at low energy, we have found that $V_{c\bar{c}N}(r)$ is attractive at short distances and screened at long distances. Our simulations are performed at a lattice cutoff of $1/a=2.0$ GeV in a spatial volume of $(3\text{fm})^3$ with the nonperturbatively $O(a)$ improved Wilson action for the light quarks and a relativistic heavy quark action for the charm quark. We will show new results of the $c\bar{c}$-nucleon potential from full QCD simulation using 2+1 flavor PACS-CS configuration as well.

Speaker: taichi kawanai (Department of Physics, Graduate School of Science, The University of Tokyo)

Slides kawanai.pdf

284 Low energy charmonium-nucleon scattering with twisted boundary conditions

We study the charmonium-nucleon interations at low energies by extended L¥"ushcer formula with partially twisted boundary conditions, which allows us to calculate the s-wave phase shift at any small value of the relative momentum even in a finite volume. Our exploratory studeis are carried out in quenched lattice QCD with non-perturbatively O(a)-improved Wilson fermions for light quarks and a relativistic heavy quark action for charm quark. We have successfully evaluated both scattering lengths and effective ranges of eta_c-nucleon and J/psi-nucleon through this new approach. We also report on preliminary results calculated on 2+1 flavor PACS-CS configuration.

Speaker: Shoichi Sasaki (University of Tokyo)

Slides sasaki.pdf

285 Flavor structure of the baryon-baryon interaction from lattice QCD

We report our recent study of the baryon-baryon interactions from lattice QCD. In the flavor SU(3) limit, two octet-baryon states are labeled by six flavor irreducible multiplet. In particular for the S-wave, there are flavor 27-plet, octet and singlet for spin singlet states(1S_0), and flavor anti-decuplet, decuplet and octet for spin triplet states(3S_1). These states provide convenient basis for two octet-baryon system in S-wave, where the interaction matrix becomes diagonal. We have extracted potentials of the interaction following the method recently developed (N. Ishii,S. Aoki and T. Hatsuda, Phys. Rev. Lett. 99, 022001 (2007)). We've found strong flavor dependence of the interaction in that basis. For example, the spin-singlet flavor-octet channel has a very strong repulsion at short distance while the spin-triplet flavor-octet channel has a very weak one. Moreover, it turns out that the spin-singlet flavor-singlet state has no repulsion at short distance but an attraction instead. It is interesting that quark models had predicted these features correctly. This provides us important information about physical origin of the baryon-baryon interaction. Our numerical results are obtained from full QCD gauge configurations in the flavor SU(3) limit corresponding to a pion mass of 834 MeV, provided by CP-PACS/JLQCD Collaborations to Japan Lattice Data Grid(JLDG)/International Lattice Data Grid(ILDG).

Speaker: Takashi Inoue (Nihon University, College of Bioresource Sciences)

Slides Inoue.pdf

286 Lattice QCD study of baryon-baryon interactions in the (S,I)=(-2,0) system using the coupled-channel formalism

We investigate baryon-baryon interactions with strangeness S=-2 and isospin I=0 system from Lattice QCD. The study of S=-2 system opens a gate of multi-strangeness hadronic world and provides the unified understanding of YN and YY interactions. A satisfactory description of YN and YY interaction is not yet obtained with use of phenomenological meson exchange model due to the lack of the direct measurement of hyperon-hyperon scattering to determine many free parameters. It is important to understand these interactions directly from QCD. In order to solve this system, we prepare three types of baryon-baryon operators (Lambda-Lambda, N-Xi and Sigma-Sigma) and construct three operators diagonalizing the 3x3 correlation matrix. Combining of these sink operators with the diagonalized source operators, we obtain nine effective Bethe-Salpeter wave functions. The 3x3 potential matrix is calculated by solving the coupled-channel Schroedinger equation. The flavor SU(3) breaking effects of the potential matrix are also discussed by comparing with the results of SU(3) limit in the same calculation. Our numerical results are obtained from 2+1 flavor QCD gauge configurations with m_pi = 870 MeV and m_pi/m_K = 0.95, provided by the CP-PACS/JLQCD Collaborations.

Speaker: Kenji Sasaki (University of Tsukuba)

Slides ksasaki.pdf

287 The study of the Three Nucleon Force in full QCD Lattice calculations

Recent researches in nuclear/astro physics are pointing to the important role of the three baryon force. It suffers, however, huge uncertainties to this date, and the direct determination from QCD is highly desirable. As a first step to obtain the complete information of the three baryon force, we study the effective two nucleon potential in the three nucleon system. The effective potential is extracted from the corresponding effective Bethe-Salpeter(BS) wave function, in which the DoF of a spectator nucleon is integrated out. In this talk, we present the results of the effective potential in triton, and the comparison with the genuine two nucleon potential is given. Calculations are carried out for m_\pi = 0.57-1.13GeV, where the dynamical clover fermion configurations generated by the CP-PACS Collaboration (N_f=2) and the PACS-CS Collaboration (N_f=2+1) are employed.

Speaker: Takumi Doi (University of Tsukuba)

Slides doi.pdf

Parallel 51: Nonzero temperature and density

288 Spectral properties of quarks above Tc -- thermal mass, dispersion relation, and self-energy --

Spectral properties of quarks above the critical temperature for deconfinement are analyzed in quenched lattice QCD on lattices of size $128^3\times16$. We study quark spectral function in energy and momentum space, focusing on the values of the thermal mass and the dispersion relations of normal and plasmino modes at nonzero momentum, as well as their spatial volume dependence. Our numerical result suggests that the dispersion relation of the plasmino mode has a minimum at nonzero momentum even near the critical temperature. The behavior of quark self-energy is also analyzed, which is found to be consistent with the spectral function extracted from the correlation function.

Speaker: Masakiyo Kitazawa (Osaka University)

Slides kitazawa.ppt

289 Longitudinal and transverse meson correlators in the deconfined phase from the lattice

It has long been known that QCD undergoes a deconfining phase transition at high temperature. One of the consequent features of this new, quark-gluon phase is that hadrons become unbounded. In this talk meson correlation functions at non-zero momentum are studied in the deconfined phase using the Maximum Entropy Method. In particular, both the longitudinal and transverse vector correlation functions are studied.

Speaker: Chris Allton (Swansea University)

Slides allton.pdf

290 THE SCALAR DOES NOT DECAY AT FINITE TEMPERATURES.

We investigate medium effects on mesonic screening lengths for QCD with 2-flavours of dynamical staggered quarks on lattices with cutoff a=1/6T. In our study, T ranges from 0.89 Tc to 1.92 Tc, spanning both the hadronic and the quark-gluon plasma phases. While chiral symmetry restoration in the vector channel appears to take place near Tc, it is seen in the scalar channel only above 1.33 Tc. Varying spatial lattice sizes, we find very little volume dependence in our results at 0.94 Tc, which is the expected critical end point temperature. This suggests that the scalar does not decay. We also comment on the nature of interactions around Tc and beyond.

Speaker: Debasish Banerjee (Tata Institute of Fundamental Research)

Slides BANERJEE.pdf

291 Lattice study of transport coefficients in second order dissipative hydrodynamics

The quark-gluon plasma produced in heavy ion collisions at RHIC energy is known to be very close to the ideal fluid. Calculations with viscosities and other transport coefficients, i.e. second order dissipative hydrodynamics is known as a causal theory, it includes many phenomenological transport coefficients. We attempt to constrain those transport coefficients by SU(3) lattice gauge calculation. On the basis of the phenomenological derivation of second order hydrodynamics by Israel-Stewart and Boltzmann-Einstein principle, we relate the Israel-Stewart parameters to fluctuations of off-diagonal components of energy-momentum tensor on the lattice and evaluate them.

Speaker: Yasuhiro Kohno (Osaka University)

Slides kohno.pdf

292 Another mean field treatment in the strong coupling limit of lattice QCD

Strong coupling lattice QCD (SC-LQCD) is a useful approach to study dense matter based on QCD. With the aid of the mean field for the chiral condensate and 1/d expansion, phase diagram has been obtained in the strong coupling limit and with the NLO / NNLO finite coupling effects. Recently, de Forcrand and Fromm investigated the phase diagram in the Monomer-Dimer-Polymer (MDP) algorithm in the strong coupling limit. The phase diagram in MDP is different in shape from that in the mean field result. The origin of this difference is not understood yet. We consider the possibility to incorporate an additional mean field in SC-LQCD, which comes from bosonizing the baryonic action and corresponds to the point split q-qbar expectation value. With this mean field, we obtain an NJL type effective potential with the variable wave function renormalization factor. We discuss the effect of this mean field on the phase boundary and compare the results with those in the MDP algorithm.

Speaker: Akira Ohnishi (Yukawa Institute for Theoretical Physics, Kyoto University)

Slides Ohnishi.pdf

Parallel 53: Algorithms and machines

293 AuroraScience

I will report on the status of the AuroraScience project ( web.infn.it/aurorascience )

Speaker: Luigi Scorzato (ECT*)

Slides 1_Scorzato_AuroraScience_Lattice2010.pdf

294 Solving the Dirac equation on QPACE

I present the implementation of a parallel solver currently used on QPACE for N_f=2 flavours of Clover fermions. I choose the mixed-precision Schwarz preconditioned FGCR algorithm in order to satisfy network bandwidth and latency constraints, to make efficient use of the multicore parallelism and on-chip memory, and to achieve flexibility in the choice of lattice sizes. I present benchmarks on up to 256 QPACE nodes showing a sustained performance of about 20% for the complete solver and very good scaling.

Speaker: Andrea Nobile (uni regensburg)

Slides nobile.pdf

295 apeNET+: a 3D toroidal network enabling petaFLOPS scale Lattice QCD simulations on commodity clusters

apeNET is a seven-years old project aimed at the acceleration of numerical simulations, mainly Lattice QCD, on commodity clusters of O(1000) nodes using a custom-designed 3D toroidal interconnect. In this paper we report on apeNET+, the new generation of our network adapters supporting wire speeds up to 34 Gbit/s per link, PCIe x8 gen 2, improved hardware RDMA support and enhanced communication primitives. The project target is the development of a low latency, high bandwidth direct network, i.e. without external switching hardware, matching the wire performance of the commercial counter-parts and improving on the price/performance ratio when the cluster size increases. apeNET is a network of point-to-point links with a 3D toroidal topology, where each processing node is directly connected to its first neighbours by six bi-directional full duplex links. We adopted a packet-based communication protocol with wormhole dimension-ordered routing and virtual channels. The network interface provides hardware support for the RDMA programming model. A Linux kernel driver, a set of low-level RDMA APIs and a OpenMPI library driver are available, enabling painless porting of standard applications. Preliminary electrical measurements are provided and status update of the hardware developments are reported.

Speaker: Roberto AMMENDOLA (INFN Roma Tor Vergata)

Slides 3_ammendola.pdf

296 Attaining multi-teraflops performance for QCD on GPUs

In recent years, graphics processing units (GPUs) have gained prominence as general-purpose computing devices that offer an order of magnitude improvement in price/performance for a range of applications, including lattice gauge theory. In this contribution, an optimized Dirac solver for Wilson and clover-improved Wilson fermions is described. We discuss strategies for achieving high performance on a single GPU and techniques for employing many GPUs in parallel. We present illustrative results for scaling to as many as 32 GPUs on production lattices, where we achieve performance in excess of 3 Tflops at much lower cost than would be possible on traditional architectures.

Speaker: Ronald Babich (Boston University)

Slides lat10_babich.pdf

297 QUDA Programming for Staggered Quarks

We have been extending the QUDA GPU code developed at Boston University to include the case of improved staggered quarks. Improved staggered quarks such as asqtad and HISQ require both first and third nearest neighbor terms in the Dirac operator. We call the corresponding links fatlinks and longlinks. The fatlinks are not unitary and staggered phases are included in the links, so link reconstruction techniques may either be inapplicable or require modification. A single precision inverter using compressed storage for the longlinks achieves a speed of 100 GF/s on an NVIDIA GTX280 GPU on a $24^3\times 32$ lattice. In addition to the inverter code, we have code for fatlink computation, gauge force and fermion force. They run at 170, 186 and 107 GF/s, respectively, for similar conditions to the solver speed above. The single GPU code is currently in production on NCSA's AC cluster for the study of electromagnetic effects. The double precision multimass solver is running at 20 GF/s, about 80\% of the speed of an 8-node or 64-core job on Fermilab's jpsi cluster. The AC cluster has C1060 Tesla boards with lower memory bandwidth than the GTX280, where the DP inverter runs at 33 GF/s. Multi-GPU code is in development.

Speaker: Steven Gottlieb Gottlieb (Indiana University)

Slides Gottlieb_Lattice2010_GPU.pdf

Parallel 55: Applications beyond QCD

298 Lattice String Field Theory

Abstract: String field theory is a candidate for a full non-perturbative definition of string theory. We aim to define string field theory on a space-time lattice to investigate its behaviour at the quantum level. Specifically, we look at string field theory in one dimension with a linear dilaton. We report the first results of our simulations.

Speaker: Francis Bursa (University of Cambridge)

Slides bursa.pdf

299 Supersymmetry on the lattice and the status of the SYM simulations

Supersymmetry has been a major interest of many theoretical investigations. These investigations should be complemented with the results of lattice simulations. However, a general formulation of supersymmetry on the lattice is still missing. I will review some strategies that allow a simulation of certain supersymmetric theories. The Münster-Desy collaboration has used the suggestion of Veneziano and Curci to simulate supersymmetric Yang-Mills theories. I will summarize the recent results concerning the spectrum of the theories and compare them with the theoretical predictions of low energy effective actions.

Speaker: Georg Bergner (Institutes für Theoretische Physik Universität Münster)

Slides bergner.pdf

300 Effects of a potential fourth fermion generation on the upper and lower Higgs boson mass bounds.

We study the effect of a potential fourth fermion generation on the upper and lower Higgs boson mass bounds. This investigation is based on the numerical evaluation of a chirally invariant lattice Higgs-Yukawa model emulating the same Higgs-fermion coupling structure as in the Higgs sector of the electroweak Standard Model. In particular, the considered model obeys a Ginsparg-Wilson version of the underlying $\mbox{SU}(2)_L\times \mbox{U}(1)_Y$ symmetry, being a global symmetry here due to the neglection of gauge fields in this model. Here we present our first results on the fermion mass dependence of the Higgs boson mass bound as well as its cutoff dependence at very heavy fermion masses.

Speaker: Philipp Gerhold (Humboldt-University Berlin)

Slides gerhold.pdf

301 The bulk transition of many-flavour QCD and the search for an UVFP at strong coupling

We explore the possibility that the observed bulk transition at N_f = 12 be identified with an ultraviolet fixed point (UVFP), whose existence has been recently conjectured by Kaplan and collaborators, based on AdS/CFT. A preliminary scaling analysis favours a first order nature of the bulk phase transition. However, we argue that the AdS/CFT inspired scenario might be realized at the endpoint of the bulk transition line, at the critical value of N_f where conformality is lost.

Speaker: Elisabetta Pallante (University of Groningen)

Slides Pallante.ppt

Parallel 57: Vacuum structure and confinement

302 Study of the QGP physics in center vortices

We study the dynamics of QGP in terms of magnetic center vortices that are responsible for the non-perturbative physics of QCD. Here we report the infrared behavior of thermal gluons and the transport coefficient of QGP before/after the center degree of freedom removed. We discuss the role of magnetic degree of freedom in the QGP physics.

Speaker: Takuya Saito (Kochi Univ.)

Slides tsaito.pdf

303 Non abelian Bianchi identities, monopoles and gauge invariance

A direct connection is proved between the Non-Abelian Bianchi Identities and the Abelian Bianchi identities for the 't Hooft tensor in a generic gauge; the existence of a magnetic current is related to the violation of NABI's. Using this relation it is shown that not all gauges are equivalent to detect monopoles on the lattice, that e.g. the Maximal Abelian Gauge is a legitimate choice while the Landau gauge is not. Nevertheless monopole condensation is found to be a gauge invariant property.

Speaker: Claudio Bonati (PI)

Slides bonati.pdf

304 The QCD vacuum wave functional and confinement in Coulomb gauge

We report results on the Coulomb-gauge ghost propagator and the color-Coulomb potential computed in two lattice gauge-field ensembles: (1) configurations derived from our recently proposed Yang-Mills vacuum wave functional in 2+1 dimensions, and (2) lattices generated by Monte Carlo simulations of the three-dimensional Euclidean SU(2) lattice gauge theory with the Wilson action. We observe remarkable agreement between the ghost propagators in both ensembles, but some differences in the potentials. Those originate from rare configurations with very small values of the lowest eigenvalue of the Coulomb-gauge Faddeev-Popov operator. If the same cuts on such exceptional configurations are applied in both ensembles, then the color-Coulomb potentials are also in reasonably good agreement.

Speaker: Stefan Olejnik (Institute of Physics, Slovak Academy of Sciences, Bratislava)

Slides olejnik.pps

305 Momentum dependence of the topological susceptibility with overlap fermions

We investigate the momentum dependence of the topological susceptibility and its derivative at zero momentum with overlap fermions. We expose the role of the low-lying Dirac eigenmodes for the topological charge density, and find a negative value for the derivative. While the sign of the derivative is consistent with the QCD sum rule in pure Yang-Mills theory, the absolute value is estimated larger if only the contribution from the zero modes and of the low-lying eigenmodes is taken into account. We also examine the effect of dynamical quarks by a reweighting method and find that it reduces the topological susceptibility for smaller quark masses and triggers the change of sign of the derivative.

Speaker: Yoshiaki Koma (Numazu College of Technology)

Slides koma.pdf

306 Quantum entanglement in SU(3) lattice Yang-Mills theory at zero and finite temperatures

Entanglement entropy measures how the spatial subregion in a total system is entangled quantum mechanically with its complement. Entanglement entropy provides with an insight into phase structures of quantum systems and attracted much interest recently. In particular, it has been argued within the models of AdS/QCD correspondence that the entanglement entropy could exhibit a non-analytic behavior with respect to the size $l$ of the subregion. We measured the entanglement entropy in SU(3) pure Yang-Mills theory (approximating it by the so called $\alpha=2$ entropy). Within the statistical errors the numerical data does not show a non-analytic behavior at zero temperature and is well fitted with the power law $1/l^3$. We also show that the entanglement entropy receives a thermal contribution at finite temperature comparable with the thermal entropy, as is expected on general grounds.

Speaker: Yoshiyuki Nakagawa Nakagawa (Niigata University)

Slides nakagawa.pdf

Parallel 59: Theoretical developments

307 Towards step-scaling with off-shell renormalisation

We apply twisted boundary conditions to off-shell Rome-Southampton non-perturbative renormalisation. This enables us to select momenta that are not necessarily a Fourier mode. The technique allows better controlled continuum extrapolation of results by removing O(4) breaking ambiguity. Continuity of the momentum scale allows us to develop a step-scaling technique that does not require fine tuning of the coupling.

Speaker: Rudy Arthur (University of Edinburgh)

Slides rudy.pdf

308 Testing universality and automatic O(a) improvement in massless lattice QCD with Wilson quarks

The chirally rotated Schroedinger functional (SF) provides a test bed for universality and automatic O(a) improvement. In joint work with Bjoern Leder, we have implemented the chirally rotated Schroedinger functional and carried out extensive quenched simulations. We demonstrate that, after proper tuning of a dimension 3 boundary counterterm, the expected chirally rotated SF boundary conditions are indeed obtained. As a result, automatic O(a) improvement is realised and we demonstrate this with a few examples. Universality of properly renormalized correlation functions is confirmed by comparing to results obtained with the standard set-up of the Schroedinger functional. As a by-product of this study the non-singlet current renormalisation constants Z_A and Z_V are obtained from ratios of 2-point functions.

Speaker: Stefan Sint (Trinity College Dublin)

Slides sint.pdf

309 Transfer Matrix for Partially Quenched QCD

Partially quenched lattice QCD is defined in euclidean space, and usually considered not be unitary. This raises the question whether effective field theory methods, such as chiral perturbation theory, can be justified in the partially quenched case. In this talk, we take a first step, in which we construct a transfer matrix for the ghost sector of partially quenched theories. While this leads to a nonhermitian hamiltonian, we show that the eigenvalues of this hamiltonian have positive real part.

Speaker: Maarten Golterman (San Francisco State University)

Slides golterman.pdf

310 Reflection positivity of the free overlap fermions.

We rigorously show that free overlap Dirac fermions on lattice satisfies the Osterwalder Schrader reflection positivity condition, which leads to the unitarity property of the corresponding quantum theory.

Speaker: Kouta Usui (University of Tokyo)

Slides usui.pdf

311 Classification and Generalization of Minimal-doubling actions

There is a chance that Minimal-doubling fermion actions will remove a numerical expense in Lattice QCD simulations although all the known examples so far lack sufficient discrete symmetries for a good continuum limit. In this talk we discuss classification and unification of Minimal-doubling actions to search for possibiliy of their application. In this context we propose a new class of Minimal-doubling actions, which might possess higher discrete symmetry than Karsten-Wilczek or Borici-Creutz actions. We also study generalization of Minimal-doubling actions to higher dimensions. We show that the parameter range within which the number of doublers becomes minimal gets narrower with the dimension going up.

Speaker: Tatsuhiro MISUMI (Yukawa Institute for Theoretical Physics, Brookhaven National Laboratory)

Slides misumi.pdf

16:10 Coffee break

Parallel 50: Hadronic structure and interactions

312 An extention to the Luescher's finite volume method above inelastic thresholds (formalism)

We propose a new method to calculate scattering amplitudes above inelastic thresholds as an extention to the Luescher's finite volume method for elastic scattering phase shifts. In the inifinite volume, the asymptotic form of hadronic Bethe-Salpeter (BS) wave functions at spatial infinity can be derived in exactly the same manner as given in Ref.[1,2,3]. It contains the information of the T-matrix of QCD in quite analogous way as the scattering theory of quantum mechanics. We introduce an energy-independent generally non-local coupled-channel interaction kernel so that it can simultaneously generate BS wave functions in wide range of energy region with an effective Schroedinger equation (coupled channel version). Note that this interaction kernel can generate T-matrix of QCD by construction. In a finite volume, scattering spectrum is discretized. Each state obtained in a finite volume system corresponds to a particular linear combination of multiple incomming states in the infinite volume. To calculate T-matrix above inelastic thresholds, we need states with different linear combinations at the same energy. However, corresponding states are located at different energies due to the discretized spectrum, which is the reason why the standard Luescher's method is usually restricted to the elastic region. Our plan is to avoid this difficulty by using the interaction kernel introduced above. We first construct the interaction kernel in a finite volume, and then use it to generate BS wave function in the infinite volume. Note that the energy independent interaction kernel is constructed by using BS wave functions from multiple energies, by which the states with different linear combinations of incomming states can be taken into account. For an interaction with finite range, the interaction kernel constructed in a finite volume is insensitive to the spatial size. (as long as the spatial size is sufficiently large) This implies that, once such interaction kernel is constructed, it can be used to generate BS wave functions at arbitrary spatial volume, which enables us to access the S-matrix of QCD in the inifinite volume. We will also discuss possible applications. Reference: [1] C.-J.D.Lin, G.Martinelli, C.T.Sachrajda, M.Testa, Nucl.Phys.B619(2001)467. [2] S.Aoki et al., CP-PACS Coll., Phys.Rev.D71(2005)094504. [3] S.Aoki, T.Hatsuda, N.Ishii., Prog.Theor.Phys.123(2010)89.

Speaker: Noriyoshi Ishii (University of Tokyo)

Slides ishii.pdf

313 Extracting Scattering Parameters using the Isospin Chemical Potential

Hadronic scattering mediated through the strong interaction has been an area of great interest for both theory and experiment. Recently, lattice QCD calculations of scattering processes from first principles have seen remarkable progress, including multiple calculations of two-pion scattering lengths that agree with experiment to within a few percent. However, there exists a certain class of scattering processes, such as pion-nucleon scattering, that contain annihilation diagrams, which are prohibitively expensive to simulate on the lattice. In this talk, I will present a method to extract certain parameters from this class of scattering processes by employing an isospin chemical potential, which can be simulated on the lattice as a result of its positive-definite fermion determinant.

Speaker: Michael Buchoff (University of Maryland, College Park)

Slides buchoff.pdf

314 The chiral and angular momentum content of the $\rho$-meson

The variational method allows one to study the mixing of interpolators with different chiral transformation properties in the nonperturbatively determined physical state. It is then possible to define and calculate in a gauge-invariant manner the chiral as well as the partial wave content of the quark-antiquark component of a meson in the infrared, where mass is generated. Using a unitary transformation from the chiral basis to the $^{2S+1}L_J$ basis one may extract a partial wave content of a meson. We present results for the $\rho$ meson using a simulations with $N_f=2$ dynamical quarks, all for lattice spacings close to 0.15 fm. We point out that these results indicate a simple $^3S_1$-wave composition of the $\rho$ meson in the infrared, like in the SU(6) flavor-spin quark model.

Speaker: Markus LIMMER (Karl-Franzens-Universitaet Graz)

Slides limmer.pdf

315 Rho decay widths from the lattice

While the masses of light hadrons have been extensively studied in lattice QCD simulations, there exist only a few exploratory calculations of the strong decay widths of hadronic resonances. We will present preliminary results of a computation of the rho meson width obtained using N_f=2+1 flavor simulations. The work is based on Luescher's formalism and its extension to moving frames.

Speaker: Julien Frison (Centre de Physique Théorique (Marseille))

Slides frison.pdf

Parallel 52: Nonzero temperature and density

316 The imbalanced Fermi gas at unitarity

Lattice field theory is a useful tool for studying strongly interacting theories in condensed matter physics. A prominent example is the unitary Fermi gas: a two-component system of fermions interacting with divergent scattering length. With Monte Carlo methods this system can be studied from first principles. In presence of an imbalance (unequal number of particles in the two components) a sign problem arises, which makes conventional algorithms inapplicable. We will show how to apply reweighting techniques to generalise the recently developed worm algorithm to the imbalance case, and present results for thermodynamic observables, in particular the critical temperature, for equal, as well as unequal number of fermions in the two spin components.

Speaker: Olga Goulko (University of Cambridge)

Slides OlgaGoulko_lat2010.pdf

317 A new approach for studying large numbers of fermions in the unitary regime

A novel lattice approach is presented for studying systems comprising a large number of interacting nonrelativistic fermions. The construction is ideally suited for numerical study of fermions near unitarity--a strongly coupled regime in which the s-wave scattering length is tuned much larger than all other physical scales. Such systems are experimentally accessible with trapped atoms, and provide a starting point for an effective field theory description of nuclear physics. I discuss the construction of our lattice theory which allows us to study systems of up to (but by no means limited to) 38 fermions with high accuracy and modest computational resources, and offer an overview of several applications of the technique. A detailed discussion of applications and simulation results will be described in companion parallel-session talks given by A. N. Nicholson and J-W. Lee.

Speaker: Michael G. Endres (Columbia University)

Slides MikeEndres.pdf

318 Lattice Study of Trapped Fermions at Unitarity

I describe a lattice study of up to N=20 unitary fermions confined to a harmonic trap. Our results show excellent agreement (within 1%) with high precision solutions to the many-body Schrodinger equation for up to N=8. We are also able to make predictions for larger N which were inaccessible by the Hamiltonian approach due to computational limitations. Harmonic traps are used experimentally to study cold atoms tuned to a Feshbach resonance. We show that they also provide certain benefits to numerical studies of many-body correlators on the lattice. In particular, we anticipate that the methods described here could be used for studying nuclear physics.

Speaker: Amy N. Nicholson (Institute for Nuclear Theory, University of Washington)

Slides AmyNicholson.pdf

319 Lattice calculation for unitary fermions in a finite box

A fundamental constant in systems of unitary fermions is the so-called Bertsch parameter, the ratio of the ground state energy for spin paired unitary fermions to that for free fermions at the same density. I discuss how we computed this parameter as well as the pairing gap using a recently developed lattice construction for unitary fermions, by measuring correlation functions for up to 38 fermions in a finite box. Our calculation illustrates interesting issues facing the study of many-body states on the lattice, which may eventually be confronted in QCD calculations as well.

Speaker: JONG-WAN LEE (University of Washington)

Slides JongWanLee.pdf

Parallel 54: Algorithms and machines

320 GPU Performnace of Conjugate Gradient Solver with Staggered Fermions

The progress in GPUs (graphic processing units) is much faster than that of CPUs. We use GPUs of nVIDIA GTX 295, GTX 285, and GTX 480 models to probe the computing performance of the conjugate gradient solver for the Dirac equations made of staggered fermions. We use MILC fine lattices (283 × 96). The performance test is done using 4 GPUs. We use CUDA v2.3 and v3.0 libraries to compile the code. The GPU performance is reviewed in great details.

Speaker: Hyung-Jin Kim (Seoul National University)

Slides 1_Kim.pdf

321 GPU-Based Conjugate Gradient Solver for Lattice QCD with Domain-Wall Fermions

We present a GPU-based conjugate gradient (CG) solver for lattice QCD with domain-wall fermion (DWF). It is well known that CG is the most time-consuming part in the hybrid Monte Carlo simulation of unquenched lattice QCD, which becomes even more computational demanding for lattice QCD with exact chiral symmetry. We have implemented the CG for a general 5-dimensional DWF operator on NVIDIA's CUDA architecture with mixed-precision, using the defect correction as well as the reliable updates algorithms. For NVIDIA's GTX 285, our CG solver for the optimal domain-wall fermion achieves 180 Gflops (sustained). Since the performances of the defect correction and the reliable updates depend on the source vector, which also change at different stages of the CG, we investigate a dynamically adaptive scheme which can pick the best one among these two algorithms such that the entire CG can attain the optimal performance.

Speaker: Yao-Yuan Mao (National Taiwan University)

Slides 2_Mao.pdf

322 Implementation of the Neuberger overlap operator in GPUs

To describe a decay like $K \to \pi\pi$ a formulation of lattice QCD has to be found which respects chiral symmetry. For this, the Dirac operator has to fulfill the Ginsparg-Wilson relation and one particular solution to this is the Neuberger overlap operator. The downside of having a chiral formulation of QCD on the lattice is that its computational costs are orders of magnitudes higher. On the other hand, recent development has shown that a lot of computing power can be gained from GPU hardware. I intend to give a review of our implementation of the Neuberger overlap operator on the GPU and give an outlook of the applications we like to aim. Topics covered include the calculation of exceptional low-modes to the Wilson-Dirac operator and the exact treatment, computation of the index of the Neuberger overlap operator and the zero-mode expansion of the propagator.

Speaker: Bjoern Walk (Institut für Kernphysik, Universität Mainz)

Slides 3_Walk.pdf

323 Domain decomposition method on GPU cluster for Lattice

The modern graphic processing unit (GPU) has become one of the powerful computational device. Applying GPU to the lattice QCD computation has been investigated especially for the inversion solver of the discretized Dirac operators. Most of the previous works on lattice QCD with GPU, however, have been done with single GPU card. Since the single GPU performance and the memory size are limited at a few TFlops and of a few GBytes, the lattice sizes are limited to rather small sizes. Thus, to simulate QCD on more realistic lattice we need a cluster system with multiple GPU’s. The GPU cluster system requires a special care on the GPU- GPU-intercommunication because the modern GPU lacks the direct GPU-GPU communication feature. In order to make a good performance with a cluster with GPU, we investigated a domain decomposition preconditioner for the O(a)-improved Wilson-Dirac fermion inverter, where the lattice is decomposed into domains. In this talk we report some performance results on the additive Schwarz preconditioner on GPU cluster computing.

Speaker: Yusuke Osaki (Hiroshima University, depertment of physical science)

Slides 4_Osaki.pdf

Parallel 56: Applications beyond QCD

324 Dimensional reduction and confinement from five dimensions

We study non-perturbatively five-dimensional gauge theories by means of the mean-field expansion on the lattice. On the anisotropic torus we show that a continuum limit can be defined where the anisotropy is a relevant parameter. The analysis of the static force supports the fact that the four-dimensional hyperplanes decouple from each other in the continuum limit. Clear signs of confinement are found in the static potential along the hyperplanes.

Speaker: Francesco Knechtli (University of Wuppertal)

Slides knechtli.pdf

325 Center Symmetry Restoration with 2 Flavor Large N Yang-Mills in the Adjoint Representation.

We report on the restoration of center symmetry in two flavor large N Yang Mills lattice field theory with dynamical fermions in the adjoint representation. Numerical evidence is given to show correlators of $P_\mu$ tend to zero in the large N limit. Wilson fermions were employed on a $2^4$ sized lattice for a variety of bare quark masses and coupling strength. We argue that this model may offer an alternative route to understanding the conformal window of Yang Mills with dynamical fermions.

Speaker: Richard Galvez (Syracuse University)

Slides RichardLattice2010.pdf

326 Orientifold Planar Equivalence: The Quenched Meson Spectrum

Orientifold Planar Equivalence is a powerful analytical tool that allows us to relate certain observables (among which, meson masses) in SU($N$) gauge theory with one (anti-)symmetric Dirac flavour and ${\cal N}=1$ SU($N$) SUSY in the limit in which the number of colours $N$ goes to infinity. This enables us in principle to transcribe SUSY results to QCD, provided that the latter is close (in the sense of an appropriate $1/N$ expansion) to its large-$N$ limit. We present a lattice study of the meson and rho mass in the quenched theory for $N$ ranging from 3 to 8, fermions in two-index irreducible representations and fixed lattice spacing. A comparison of the spectra among the various theories allows us to estimate the size of the expected corrections at finite $N$. Consequences of our findings for the application of Orientifold Planar Equivalence to study real-world QCD are discussed.

Speaker: Biagio Lucini (Swansea University)

Slides lucini.pdf

327 Lattice Wess-Zumino Model Simulation with GPUs

We describe our studies of the lattice Wess-Zumino model with overlap type operators, using GPUs. We have checked that at one loop there is a nonrenormalization of the superpotential, and that in the simulations the simplest Ward identity of the continuum theory is satisfied to a good approximation at weak coupling.

Speaker: Joel Giedt (RPI)

Slides giedt.pdf

Parallel 58: Vacuum structure and confinement

328 Properties of gauge orbits

In gauge theories, all physically equivalent field configurations lie on a common gauge orbit. Selecting a particular representative on the gauge orbit fixes a gauge. This is useful for practical reasons, like to facilitate calculations of gauge-invariant observables, or to provide gauge-dependent correlation functions which can serve as input for methods other than lattice. It is also of fundamental interest, as many questions, e.g. related to confinement and interactions of gluons, can be most easily formulated in a fixed gauge. However, non-perturbatively the presence of Gribov copies complicate a unique choice, affecting correlation functions severely at or below scales of 1 GeV. This non-perturbative structure of gauge orbits is investigated in detail using lattice gauge theory. In particular, possibilities how to define and implement consistently the non-perturbative extensions of the Landau gauge are discussed. This includes many details on the properties of gauge orbits, and thus of the underlying structure of gauge theories on the level of the gauge fields. Also, the resulting gauge-dependence of correlation functions will be presented.

Speaker: Axel Maas (Karl-Franzens-University Graz)

Slides mass.pdf

329 Universal Aspects of Deconfinement: Interfaces, Flux Tubes and Self-Duality in 2+1 Dimensions

We study center vortex free energies and ’t Hooft’s electric fluxes on the lattice in 2+1 dimensions, where SU(2) for example, is in the universality class of the 2d Ising model. This places a wealth of exact results at our fingertips. In particular, spacelike center vortices in SU(2) near criticality correspond to spin interfaces in the 2d Ising model, whose universal scaling functions are known exactly. We exploit this to locate the deconfinement transition with unprecedented precision and subsequently for a finite size scaling analysis, where the self-duality of the 2d spin model is reflected in a duality between the spacelike vortices and confining electric fluxes. The corresponding relation between the string tension and its dual in the high temperature phase is arguably the simplest example of a universal amplitude ratio. Around the transition, both can be efficiently extracted from the exact results with a global one-parameter fit which allows straightforward continuum extrapolation.

Speaker: Lorenz von Smekal (TU Darmstadt)

330 Gauge-independent "Abelian" dominance and magnetic monopole dominance in SU(3) Yang-Mills theory

Recently we have proposed a new reformulation of Yang-Mills (YM) theory based on new variables on a lattice by extending the Cho-Faddeev-Niemi-Shabanov decomposition. Our reformulation allows options discriminated by the stability group $\tilde{H}$ of the gauge group $G$. When $\tilde{H}$ agrees with the maximal torus group $H$, it reduces to a manifestly gauge-independent reformulation of the conventional Abelian projection in the maximal Abelian gauge. Within this framework, a non-Abelian Stokes theorem enables us to express the Wilson loop operator in the fundamental representation by the ``Abelian" variable extracted in association with the stability group in the minimal option, and to rewrite the Wilson loop operator using a non-Abelian magnetic monopole defined in a manifestly gauge-independent way. For $G=SU(3)$, two options are possible: minimal one with $\tilde{H}$ $=U(2)$ and maximal one with $\tilde{H}=H= U(1) \times U(1)$. In this talk we summarize the results of Monte Carlo simulations for $SU(3)$ in the minimal option. Especially, we compare three Wilson loop averages defined by the ``Abelian" variable, the monopole part and the original YM field. We confirm that the quark--antiquark confining potential is reproduced by the ``Abelian" variable (``Abelian" dominance), and that the string tension is reproduced by the non-Abelian magnetic monopole (magnetic monopole dominance). Moreover, we mention the behaviors of correlation functions for new variables.

Speaker: Akihiro Shibata (Computing Reaearch Center, KEK)

331 Confinement in G2 gauge theories

G2 is the smallest simple and simply connected lie group with a trivial center. Therefore investigations of G2 gauge theory may help to clarify the relevance of center symmetry for confinement. Beside this it has an intriguing connection to QCD where the center symmetry is broken by dynamical quarks transforming under the fundamental representation. In both theories the flux tube between static quarks can break due to dynamical particle production. In this talk we will present our results obtained with monte carlo simulations for the static quark-antiquark potential in different representations and we will show casimir scaling at intermediate distances and string breaking at larger distances.

Speaker: Björn Wellegehausen (TPI, University Jena)

Slides WELLEGEHAUSEN.pdf

Parallel 60: Theoretical developments

332 Quantum entanglement and KPZ relations

The entanglement of inaccessible subsystems of a quantum system may modify, under certain conditions, the universality class of its phase transitions. Numerical experiments on critical Ising model in two dimensions indicate that its modified universality class is well described by the Knizhnik-Polyakov-Zamolodchikov relations.

Speaker: Ferdinando Gliozzi (TO)

Slides gliozzi.pdf

333 Fisher's zeros as boundary of RG flows in complex coupling space

We discuss the possibility of extending the RG flows to complex coupling spaces. We argue that the Fisher's zeros are located at the boundary of the complex basin of attraction of IR fixed points. We support this picture with numerical calculations at finite volume for 2D O(N) models and the hierarchical Ising model using the two-lattice matching method. We present numerical evidence supporting the idea that, as the volume increases, the Fisher's zeros of 4D pure gauge SU(2) lattice gauge theory with a Wilson action, stabilize at a distance larger than 0.1 from the real axis in the complex beta=4/g^2 plane. We show that when a positive adjoint term is added, the zeros get closer to the real axis. We compare the situation with the U(1) case. We discuss the implications of this new framework for proofs of confinement and searches for nontrivial IR fixed points in models beyond the standard model.

Speaker: Yannick Meurice Meurice (University of Iowa)

Slides meurice.pdf

334 A Ginsparg Wilson renormalisation group approach to lattice CP symmetry

Until recent work, chiral gauge theories constructed on the lattice have violated CP symmetry. This has caused difficulties in constructing, for example, the electroweak theory on the lattice ,where applying standard CP symmetry generates a non-local shift in the fermion propagator in the presence of a Higgs field. Starting from Wilson's formulation of the re-normalisation group, using a similar procedure to that originally used to derive the Ginsparg-Wilson relation, I demonstrate that CP symmetry has to be modified when applied to the lattice. Extending the recent ideas of Igarashi and Pawlowski, and building on a renormalisation group construction of the overlap formalism, I show that on the lattice one should use a modified form of CP symmetry, which solves the various anomalies in chiral gauge theories and which can be applied to the family of chiral symmetry transformations satisfied by overlap fermions. This method can be easily extended to other Ginsparg-Wilson lattice Dirac operators.

Speaker: Nigel Cundy (Universität Regensburg)

Slides cundy.pdf

Other activities

Saturday, 19 June

Session 9

335 Technicolor phenomenology

Speaker: R. Sekhar Chivukula (Michigan State University)

Slides Chivukula_Lattice2010.pdf

336 Strong coupling expansion monte carlo

Speaker: Ulli Wolff (Humboldt University)

Slides Wolff_Lattice2010.pdf

337 Graphene: from material science to particle physics

Speaker: Joaquin Drut (The Ohio State University)

Slides Drut_Lattice2010.pdf

10:00 Coffee break

Session 10

338 Nuclear physics on the lattice

Speaker: Tetsuo Hatsuda (Phys. Dep., Univ. Tokyo)

Slides Hatsuda_Lattice2010_web.pdf

339 Light flavors on the lattice

Speaker: Jack Laiho

Slides Laiho_Lattice2010.pdf

Closing