# Gauge/Gravity Duality 2015

from to (Europe/Rome)
at The Galileo Galilei Institute for Theoretical Physics (GGI)
Arcetri, Florence
 Email ggiw1@fi.infn.it
Go to day
• Monday, 13 April 2015
• 08:15 - 08:55 Registration
• 08:55 - 09:00 Welcome 5'  Speaker: Nick Evans
• 09:00 - 12:50 Morning session
• 09:00 Electric fields and quantum wormholes 40'
A classical Einstein-Rosen bridge changes the topology of spacetime, allowing (for example) electric field lines to penetrate it. It has recently been suggested that in the bulk of a theory of quantum gravity, the quantum entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the quanta, or a “quantum wormhole”. For this “ER=EPR” correspondence to make sense it then seems necessary for a quantum wormhole to allow (for example) electric field lines to penetrate it. I will discuss (within low-energy effective field theory) whether or not this happens.


 Speaker: Nabil Iqbal Material:
• 09:40 Transport in holographic systems with momentum dissipation 40'
Gauge/gravity duality can be used to study the transport properties of strongly interacting systems with no quasiparticles. I will give an overview of some holographic toy models of states like this, in which momentum is not conserved and thus the transport of energy and charge is non-trivial. I will describe how the transport properties of the most basic such example can be understood in terms of two simple, non-holographic, effective theories, one of which is valid when momentum dissipates slowly and one when it dissipates quickly.
 Speaker: Richard Davison Material:
• 10:20 Coffee break 30'
• 10:50 Disorder in AdS/CFT 30'  Speaker: Leopoldo Pando Zayas Material:
• 11:20 Holographic Charged Impurities 30'
I will study the effect of charged impurities on holographic superconductors and brane intersections. Interestingly, for the former setup one can observe that for long enough system size the noise suppress superconductivity. I will present results for the conductivity of these disordered systems.
 Speaker: Daniel Arean Material:
• 11:50 Electromagnetic properties of charged viscous fluids: from string theory to electrons 30'  Speaker: Davide Forcella Material:
• 12:20 Holographic Conductivity: Insulators, Supersolids, and scaling 30'  Speaker: Elias Kiritsis Material:
• 12:50 - 14:20 Lunch break
• 14:20 - 18:10 Afternoon session
• 14:20 Generalized Global Symmetries 40'
We will discuss in a systematic way a generalization of ordinary global symmetries, whose charged operators are line operators, surface operators, etc., and whose charged excitations are strings, membranes, etc. Many of the properties of ordinary global symmetries apply here. They lead to Ward identities and hence to selection rules on amplitudes. Such global symmetries can be coupled to classical background fields and they can be gauged by summing over these classical fields. These generalized global symmetries can be spontaneously broken (either completely or to a subgroup). They can also have ’t Hooft anomalies, which prevent us from gauging them, but lead to ’t Hooft anomaly matching conditions. Such anomalies can also lead to anomaly inflow on various defects and exotic Symmetry Protected Topological phases. Our analysis of these symmetries gives a new unified perspective of many known phenomena and uncovers new results.
 Speaker: Nathan Seiberg Material:
• 15:00 The Holographic Goldstino 40'
We find the fingerprints of the Goldstino associated to spontaneous supersymmetry breaking at strong coupling, using holography. The Goldstino massless pole arises in two-point correlators of the supercurrent, due to contact terms in supersymmetry Ward identities. We show how these contact terms are obtained from the holographic renormalization of the gravitino sector, independently of the details of the background solution.
 Speaker: Matteo Bertolini Material:
• 15:40 Rigid Holography and the 6D (2,0) CFT on AdS_5*S^1 30'
Field theories on anti-de Sitter (AdS) space can be studied by realizing them as low-energy limits of AdS vacua of string/M theory. In an appropriate limit, the field theories decouple from the rest of string/M theory. Since these vacua are dual to conformal field theories, this relates some of the observables of these field theories on anti-de Sitter space to a subsector of the dual conformal field theories. We exemplify this rigid holography' by studying in detail the six-dimensional ${\cal N}=(2,0)$ $A_{K-1}$ superconformal field theory (SCFT) on $AdS_5\times \mathbb{S}^1$, with equal radii for $AdS_5$ and for $\mathbb{S}^1$. We choose specific boundary conditions preserving sixteen supercharges that arise when this theory is embedded into Type IIB string theory on $AdS_5\times \mathbb{S}^5 / \mathbb{Z}_K$. On $\mathbb{R}^{4,1}\times \mathbb{S}^1$, this six-dimensional theory has a $5(K-1)$-dimensional moduli space, with unbroken five-dimensional $SU(K)$ gauge symmetry at (and only at) the origin. On $AdS_5\times \mathbb{S}^1$, the theory has a $2(K-1)$-dimensional moduli space' of supersymmetric configurations. We argue that in this case the $SU(K)$ gauge symmetry is unbroken everywhere in the moduli space' and that this five-dimensional gauge theory is coupled to a four-dimensional theory on the boundary of $AdS_5$ whose coupling constants depend on the moduli'. This involves non-standard boundary conditions for the gauge fields on $AdS_5$. Near the origin of the moduli space', the theory on the boundary contains a weakly coupled four-dimensional ${\cal N}=2$ supersymmetric $SU(K)$ gauge theory. We show that this implies large corrections to the metric on the moduli space'. The embedding in string theory implies that the six-dimensional ${\cal N}=(2,0)$ theory on $AdS_5\times \mathbb{S}^1$ with sources on the boundary is a subsector of the large $N$ limit of various four-dimensional ${\cal N}=2$ quiver SCFTs that remains non-trivial in the large $N$ limit. The same subsector appears universally in many different four-dimensional ${\cal N}=2$ SCFTs. We also discuss a decoupling limit that leads  to ${\cal N}=(2,0)$ little string theories' on $AdS_5\times \mathbb{S}^1$.
 Speaker: Micha Berkooz Material:
• 16:10 Coffee break 30'
• 16:40 Quark mass in backreacted holographic QCD 30'
QCD has an interesting dependence on the quark mass, in particular near the edge of the conformal window at large N_f. This can be studied by using holographic bottom-up models for QCD in the Veneziano limit (V-QCD) where the flavor fully backreacts to the glue. I will sketch the phase diagram as a function of the quark mass and x=N_f/N_c, and discuss phenomena such as the hyperscaling relations of the meson masses and the discontinuity of the S-parameter in the conformal window. I will show how the phase diagram in the presence of a double trace deformation ~(\bar q q)^2 is obtained.
 Speaker: Matti Jarvinen Material:
• 17:10 Nuclear shadowing in the holographic framework 30'  Speaker: Pietro Colangelo Material:
• 17:40 Light-Front Holography and New Advances in Nonperturbative QCD 30'
One of the most fundamental problems in Quantum Chromodynamics is to understand the origin of the mass scale which controls the range of color confinement and the hadronic spectrum. We show that a mass gap and a fundamental color confinement scale arise when one extends the formalism of de Alfaro, Fubini and Furlan to frame-independent light-front Hamiltonian theory. Remarkably, the resulting light-front potential has a unique form of a harmonic oscillator in the light-front invariant impact variable if one requires that the action remains conformally invariant. The result is a single-variable relativistic equation of motion for qq¯ bound states, a "Light-Front Shr\"odinger Equation", analogous to the nonrelativistic radial Schr\"odinger equation, which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number and orbital angular momentum. The same equations with the correct hadron spin dependence arise from the holographic mapping of modified AdS5 space with a specific dilaton profile. A fundamental mass parameter ? appears, determining the hadron masses and the length scale which underlies hadron structure. Quark masses can be introduced to account for the spectrum of strange hadrons. This Light-Front Holographic approach predicts not only hadron spectroscopy successfully, but also hadronic form factors, the QCD running coupling at small virtuality, and the light-front wavefunctions of hadrons. Thus the combination of light-front dynamics, its holographic mapping to gravity in a higher-dimensional space and the dAFF procedure provides new insight into the physics underlying color confinement, chiral invariance, and the QCD mass scale.
 Speaker: Stanley Brodsky Material:
• 18:10 - 19:30 Reception
• Tuesday, 14 April 2015
• 09:00 - 12:50 Morning session
• 09:00 The Membrane Paradigm at large D 40'  Speaker: Shiraz Minwalla Material:
• 09:40 Entanglement Entropy and Boundary Terms: Two Short Stories 40'
Conformal transformations to hyperbolic space are a useful tool for calculating entanglement entropies in conformal field theories. I will use this tool to calculate thermal corrections to entanglement entropy for conformal field theories on spheres. I will also consider the universal log contribution to the entanglement entropy for CFTs in even dimensional flat space. In both cases, we will see the crucial role played by boundary terms.
 Speaker: Christopher Herzog Material:
• 10:20 Coffee break 30'
• 10:50 Twisted index of 3d gauge theories 30'
We discuss general results for a generalized twisted partition function of 3d gauge theories on S^2 X S^1 which are relevant for the holographic interpretation of supersymmetric AdS4 black holes.
 Speaker: Alberto Zaffaroni Material:
• 11:20 A menagerie of non-relativistic physics 30'
Spacetime symmetries lead to non-perturbative constraints on transport, like the Einstein relation between electric and thermal conductivity. I will discuss some recent progress in the understanding of the spacetime symmetries of non-relativistic systems, like the quantum and anomalous Hall effects, as well as the corresponding implications for transport. Unexpectedly, these results also shed light on so-called warped CFTs in two dimensions — a sort of chiral, non-Lorentz-invariant (and so non-relativistic) CFT — which are motivated by string theory but have remained mysterious.
 Speaker: Kristan Jensen Material:
• 11:50 BPS Wilson loops and an exact result for the Bremsstrahlung function in ABJM model 30'
We discuss results and quantum properties of a family of generalized fermionic Wilson loops in ABJ(M) theory. We propose an all-order prescription for computing the Bremsstrahlung function associated to the 1/2-BPS cusp in terms of this family of WL. The validity of this prescription is a non-trivial test of the AdS4/CFT3 correspondence.
 Speaker: Silvia Penati Material:
• 12:20 Supersymmetric AdS(5) solutions of massive type IIA supergravity 30'
We discuss the classification of generic N = 1 supersymmetric  AdS(5) x M solutions of massive type IIA supergravity and the discovery of new analytic ones. The necessary and sufficient conditions  for supersymmetry amount to a system of differential conditions on a local identity structure on M. Known AdS(5) solutions of  type IIA supergravity are reproduced by the latter. Upon making  further assumptions, the system reduces to an ODE whose analytic solution yields new AdS(5) backgrounds with non-zero Romans mass; M is  topologically a three-sphere fibered over a Riemann surface of  negative curvature. The holographically dual 4d SCFTs conjecturally arise by compactifying 6d (1,0) SCFTs on a Riemann surface.
 Speaker: Achilleas Passias Material:
• 12:50 - 14:20 Lunch break
• 14:20 - 17:50 Parallel Session : A
• 14:20 Turbulent strings in AdS/CFT 30'
I will talk about nonlinear dynamics of the flux tube between an external quark-antiquark pair in N=4 SYM using the dual string description in AdS/CFT. Perturbing the endpoints of the string and numerically computing its nonlinear time evolution, I will show that cusps can be formed on the string. I will discuss a connection between this phenomenon and turbulent behavior in the energy spectrum.
 Speaker: Takaaki Ishii Material:
• 14:50 Holographic Charge Oscillations 30'
The Reissner-Nordstrom black hole provides the prototypical description of a holographic system at finite density. We study the response of this system to the presence of a local, charged impurity. Below a critical temperature, the induced charge density, which screens the impurity, exhibits oscillations. These oscillations can be traced to the singularities in the density-density correlation function moving in the complex momentum plane. At finite temperature, the oscillations are very similar to the Friedel oscillations seen in Fermi liquids. However, at zero temperature the oscillations in the black hole background remain exponentially damped, while Friedel oscillations relax to a power-law.
 Speaker: Mike Blake Material:
• 15:20 Holographic three-dimensional YM with compressible matter 30'
We present the holographic dual of strongly coupled, three-dimensional Yang-Mills theories with massless flavour in the Veneziano limit at finite quark density. The fundamental degrees of freedom are modelled by a distribution of D6-branes backreacting the geometry of a stack of colour D2-branes. A finite chemical potential corresponds to the time component of a gauge field living on the flavour branes. We discuss the RG flows triggered by the presence of the charge density and argue that generically the IR is governed by a fixed point with particular scaling properties. We finally comment on interesting observables sensible to the different regimes of the system.
 Speaker: Anton Faedo Material:
• 15:50 Coffee break 30'
• 16:20 Universal properties of cold holographic matter 30'
I will briefly review the Landau-Fermi liquid theory and then discuss the holographic counterpart by modeling the cold matter in terms of D-brane intersections. I will focus on determining universal properties of these systems and study them at finite temperature, charge density, and magnetic fields. In particular, I will present analytic results for the diffusion constants and the zero sound dispersions. Finally, I will explore the (2+1)-dimensional anyonic liquids.
 Speaker: Niko Jokela Material:
• 16:50 Flux and Hall states in Chern-Simons matter theories with flavor 30'  Speaker: Dimitrios Zoakos Material:
• 17:20 Horava-Lifshitz Gravity from Dynamical Newton-Cartan Geometry 30'
It will be shown that (non-)projectable Horava-Lifshitz gravity and the dynamics of (twistless torsional) Newton-Cartan geometry are one and the same thing.
 Speaker: Jelle Hartong Material:
• 14:20 - 17:50 Parallel Session : B  Location: Room B
• 14:20 Superconformal Quantum Mechanics and Emerging Holographic QCD 30'
The observed light-hadron spectrum will be described from a superconformal semiclassical approximation to light-front QCD and its embedding in AdS space.  This procedure uniquely determines the confinement potential for arbitrary spin. To this end, we will show that wave equations in AdS space are dual to light-front supersymmetric quantum mechanical bound-state equations in physical space-time. The specific breaking of dilatation invariance within the supersymetric algebra explains hadronic properties common to light mesons and baryons,  such as the observed mass pattern in the radial and orbital excitations, as well as their distinctive and systematic features. Furthermore, the generalized supercharges connect the baryon and meson spectra. The lowest-lying state, the the pi-meson, is massless in the chiral limit and has no supersymmetric partner. Preliminary results extending the supersymmetric relations across the heavy-light hadronic spectrum will also be presented.
 Speaker: Guy De Teramond Material:
• 14:50 Pion resonances in Holographic QCD 30'
We investigate the leptonic decay constants of pion resonances using a 5-d holographic model for Quantum Chromodynamics (Holographic QCD). We obtain a generalized version of the  partially conserved axial current (PCAC) relation that includes the pion resonances. In the chiral limit, we find that the decay constants vanish, confirming a prediction from nonperturbative QCD based on the Bethe-Salpeter equations.
 Speaker: Alfonso Ballon-Bayona Material:
• 15:20 All order linearized hydrodynamics from fluid-gravity correspondence 30'  Speaker: Michael Lublinsky Material:
• 15:50 Coffee break 30'
• 16:20 Holographic Superconductors in Helical Backgrounds and Homes' Relation 30'
We present results on a holographic s-wave superconductor in a helically symmetric Bianchi VII symmetric space-time, and discuss the validity of Homes' law in this system. We determine the phase diagram in terms of the helix parameters, and the AC conductivity of the different phases. We in particular show that Homes' relation holds for an regime of intermediary momentum relaxation strength. For both weak and very strong lattice perturbations, i.e. weak and strong momentum dissipation, Homes' relation is violated.
 Speaker: Rene Meyer Material:
• 16:50 On Holographic Insulators and Supersolids 30'
We find holographic insulators and superconductors with a hard gap and a discrete spectrum, from an Einstein-Maxwell-scalar system in a fractionalized phase. The ground state of the system has a hyperscaling violating geometry in the IR. We break the translational invariance by adding massless scalar fields responsible for momentum dissipation.
 Speaker: Jie Ren Material:
• 17:20 Analogue holographic correspondence in optical metamaterials 30'
We assess the prospects of using optical metamaterials for simulating various aspects of analogue gravity and holographic correspondence. Albeit requiring a careful engineering of the dielectric media, some hallmark features reminiscent of the conjectured 'generalized' (non-AdS/non-CFT) holography can be detected by measuring non-local optical field correlations. The possibility of such simulated behavior might also shed light on the nature of certain ostensibly holographic phenomena in the condensed matter, optical, and AMO systems with emergent effective metrics which may not, in fact, require any reference to the original string-theoretical holography.
 Speaker: Dmitri Khveschenko Material:
• Wednesday, 15 April 2015
• 09:00 - 12:50 Morning session
• 09:00 Holographic Quantum Hall Ferromagnetism 40'  Speaker: Charlotte Kristjansen Material:
• 09:40 Is the composite fermion a Dirac particle? 40'
The theory of the fractional quantum Hall effect is based on the notion of the composite fermion, which is the low-energy quasiparticle for filling factor close to 1/2. I will show that the particle-hole symmetry of the half-filled Landau level implies that the composite fermion is a Dirac particle, characterized by a Berry phase of $pi$ around the Fermi surface.  Physical consequences are discussed.
 Speaker: Dam Thanh Son Material:
• 10:20 Coffee break 30'
• 10:50 Holographic graphene bilayers 30'
The possibility of inter-layer exciton condensation in holographic models of a strongly coupled double monolayer Dirac semi-metal are studied in detail. It is showed that, when the charge densities on the layers are exactly balanced so that, at weak coupling, the Fermi surfaces of electrons in one monolayer and holes in the other monolayer would be perfectly nested, inter-layer condensates can form for any separation of the layers. The case where both monolayers are charge neutral is special. There, the inter-layer condensate occurs only for small separations and is replaced by an intra-layer exciton condensate at larger separations. The phase diagram for charge balanced monolayers for a range layer separations and chemical potentials is found. We also show that, in semi-metals with multiple species of massless fermions, the balance of charges required for Fermi surface nesting can occur spontaneously by breaking some of the internal symmetry of the monolayers. This could have important consequences for experimental attempts to find inter-layer condensates.
 Speaker: Gianluca Grignani Material:
• 11:20 Monopoles and magnetic oscillations in holographic liquids 30'
We study monopoles and the role of magnetic field in holographic models of compressible phases of quantum matter, both from a bottom-up and a top-down approach. The former extends previous electron star models to include a magnetic field at finite temperature, while the latter is based on D-brane constructions. I will present these models and their most interesting features, such as quantum oscillations which differ from those predicted by Fermi liquid theory.
 Speaker: Valentina Giangreco Puletti Material:
• 11:50 Diffusion and incoherence 30'
Charge and heat diffusion are essential handles to grasp the transport of strongly coupled systems where momentum is quickly dissipated. Holography without momentum conservation allows to compute the diffusion constants and explore the formulation of (possibly general) bounds in analogy with the eta/s bound. The talk focuses on the description of the diffusion constants computation and properties highlighting the strength and limitations of the associated conjectured bounds, especially in view of attacking the strange metal transport physics from the diffusion side.
 Speaker: Daniele Musso Material:
• 12:20 Semiholography, conductivity and Ward identities 30'
In semiholography, a strongly-coupled conformal field theory with a holographic dual is coupled to another theory that is weakly interacting. We show how semiholography is set up in accordance with the Ward identities of the total theory. As an example, we charge fermions in the total theory under a U(1) gauge field, and compute the total electrical conductivity and Ward identity corresponding to charge conservation. The resulting conductivity can be expressed in vacuum CFT correlators which we compute in the dual holographic spacetime. Most importantly one has to include the 3-point vertex in the curved background for consistency.
 Speaker: Umut Gursoy Material:
• 12:50 - 14:20 Lunch break
• 14:20 - 17:50 Parallel Session: A  Location: Room A
• 14:20 Entanglement entropy associated to a far-from-equilibrium energy flow 30'
The time evolution of the energy transport triggered in a strongly coupled quantum critical system by a temperature gradient is holographically related to the evolution of an asymptotically AdS black brane with a gradient in its planar horizon. A relevant observable that provides physical insight about the evolution of this system and the eventual formation of a steady state is the entanglement entropy. In this talk, I will present an overview of this problem, along with results for the entanglement entropy in the regime where the difference in temperatures is small.
 Speaker: Daniel Fernandez Material:
• 14:50 Holographic magneto-transport and strange metals 30'
In this talk we analyze the thermo-electric transport properties of a strongly coupled, planar medium in the presence of an orthogonal magnetic field and disorder. Even though the analysis is performed within the gauge/gravity framework, we propose and argue for a possible universal relevance of the results relying on comparisons and extensions of previous hydrodynamical analyses and experimental data for strange metals.
 Speaker: Andrea Amoretti Material:
• 15:20 Testing the membrane paradigm with holography 30'
For an asymptotic observer a black hole can be replaced by a simple dissipative membrane located at a stretched horizon, i.e. a very small distance outside the horizon. In this talk I will show what are the limits of validity of such approximation scheme. In particular I will argue that it generically fails to capture massive quasinormal modes. I will also show how it instead reproduces hydrodynamical modes of and AdS black brane as long as an additional spurious excitation is removed from the spectrum.

 Speaker: Natalia Pinzani Fokeeva Material:
• 15:50 Coffee break 30'
• 16:20 Thermoelectric Conductivities at Finite Magnetic Field and the Nernst effect 30'
We study electric, thermoelectric, and thermal conductivities of a strongly correlated system in the presence of magnetic field by gauge/gravity duality. We consider a general class of Einstein-Maxwell-Dilaton theory with axion fields imposing momentum relaxation. Analytic general formulas for DC conductivities and the Nernst signal are derived in terms of the black hole horizon data. For an explicit model study we analyse in detail  the dyonic black hole modified by momentum relaxation. In this model, the Nernst signal shows a typical vortex-liquid effect when momentum relaxation effect is comparable to chemical potential. We compute all AC electric, thermoelectric, and thermal conductivities by numerical analysis and confirms that their zero frequency limits precisely reproduce our analytic formulas, which is a non-trivial consistency check of our methods. We discuss the momentum relaxation effect on conductivities including cyclotron resonance poles.
 Speaker: Yunseok Seo Material:
• 16:50 Electron-Phonon interactions, MIT and Holographic Massive Gravity 30'
Massive gravity is holographically dual to ''realistic'' materials with momentum relaxation. In its fully covariant formulation it in fact provides an holographic effective description for electron-phonon interactions. I will show how phonons' degrees of freedom are enconded in massive gravity and which are the interesting phenomenological features concerning the transport properties of the dual theory. In particular non-linear interactions in the phonons-sector can provide a metal-insulator crossover and a pinned response in the optical Conductivity.
 Speaker: Matteo Baggioli Material:
• 17:20 Spontaneous Breaking of U(N) symmetry in invariant Matrix Models 30'
Matrix Models have a strong history of success in describing a variety of situations, from nuclei spectra to conduction in mesoscopic systems, from strongly interacting systems to various aspects of mathematical physics, from holographic models to supersymmetric theories in the localization limit. Traditionally, the requirement of base invariance has lead to a factorization of the eigenvalue and eigenvector distribution and, in turn, to the conclusion that invariant models describe extended systems.
Moreover, Wigner-Dyson statistics for the eigenvalues is a hallmark of eigenvector delocalization. Thus, in virtually all applications of matrix models, eigenvectors are discarded and one considers just the eigenvalues. We show that deviations of the eigenvalue statistics from the Wigner-Dyson universality reflects itself on the eigenvector distribution and that a gap in the eigenvalue density breaks the U(N) symmetry to a smaller one. Moreover, this spontaneous symmetry breaking means that egeinvectors become localized and that the system looses ergodicity and that the system has lost replica symmetry invariance.
We also consider models with log-normal weight, such as those emerging in Chern-Simons and ABJM theories. Their eigenvalue distribution is intermediate between Wigner-Dyson and Poissonian, which candidates these models for describing a system intermediate between the extended and localized phase. We show that they have a much richer energy landscape than expected, with their partition functions decomposable in a large number of equilibrium configurations, growing exponentially with the matrix rank. We argue that this structure is a reflection of the non-trivial (multi-fractal) eigenvector statistics.
 Speaker: Fabio Franchini Material:
• 14:20 - 17:50 Parallel Session: B  Location: Room B
• 14:20 The local renormalization group equation in superspace 30'
The superspace formulation of the local renormalization group  equation is discussed. This is framework in which the constraints of holomorphy and R-symmetry on supersymmetric RG flows are manifest. Background fields are used to define the super-Weyl symmetry off-criticality and to derive the consistency conditions associated with this symmetry. An analog of the "a-maximization" equation, which is valid off-criticality is introduced. This machinery is also applied to the study of conformal manifolds and a simple proof is given that the metric on such manifolds is Kahler.
 Speaker: Roberto Auzzi Material:
• 14:50 Looking for an on-shell regulator 30'
A generic QFT without mass gap may present IR and UV divergencies, which must be regularized before making sense of them. In a Feynman diagram, one thinks of these divergencies as arising from an infinite integration region for a certain off-shell momentum. When one treats the theory purely on-shell, these divergencies must be seen (and regularized) in some other way. In this talk I present an approach to tackle this problem, in the particular case of divergencies of scattering amplitudes, using the so-called on-shell diagrams.
 Speaker: Eduardo Conde Pena Material:
• 15:20 Holographic Representation of Bulk Fields and Locality in (A)dS 30'
The study of local physics in a theory of quantum gravity is an important problem. (A)dS/ CFT gives us a platform to study this issue from the CFT perspective. The construction of local bulk scalars in semiclassical limit of AdS/ CFT is well-known at order by order in 1/N perturbation. Here we discuss the recent developments on this topic and in particular describe how to extend this program for fields with spin- 1 and higher. We work in both AdS and dS spaces. Local field construction is also made at arbitrary cut-off surfaces in (A)dS and their prospective connections to holographic RG are explored. Finally we argue about various finite N scenarios and their effects on bulk locality and black hole information paradox. Based on 1204.0126, 1408.0415, 1411.4657, 1501.XXXXX and related works.
 Speaker: Debajyoti Sarkar Material:
• 15:50 Coffee break 30'
• 16:20 Fermi gas formulation for D-type quivers 30'
I will explain that the exact partition function of D-type N=4 quivers SCFTs on a three-sphere coincides with the partition function of a gas of free fermions in one dimension with a non-standard Hamiltonian. I will describe briefly the mirror dual quiver theories and show that mirror symmetry is expressed as a simple canonical transformation on the density operator of the quantum mechanics. Finally I will discuss the exact evaluation of the perturbative part of the free energy for these theories, which takes the form an Airy function, and emphasize the perspectives for holography.
 Speaker: Benjamin Assel Material:
• 16:50 Scale vs. Conformal Invariance in Holography with Higher Derivative Corrections 30'
Gravitational theories with higher derivative corrections in AdS are dual to non-unitary QFTs. In particular, these may provide holographic examples of scale but not conformally invariant field theories (SFT). A distinct signature of a SFT is the non-vanishing scale anomaly R^2, which may be computed holographically. We perform a systematic near-boundary analysis of relevant gravitational theories. Generically the R^2 anomaly is not present. However we identify a very special class of theories (e.g. Chern-Simons gravity in 5d) with non-standard near-boundary behaviour. For these theories the R^2 anomaly may be present.
 Speaker: Yegor Korovin Material:
• 17:20 Entanglement entropy in a holographic model of the Kondo effect. 30'
My starting point is a holographic model of the Kondo effect recently proposed by Erdmenger et. al., i.e. of a magnetic impurity interacting with a strongly coupled system. Specifically, I focus on the challenges of computing gravitational backreaction in this model, which demands a study of the Israel junction conditions. I present general results on these junction conditions, including analytical solutions for certain toy models, that may be relevant also more generally in the AdS/boundary CFT correspondence. Furthermore, similar junction conditions for a bulk Chern-Simons field appearing in the holographic Kondo model are discussed. I then focus on the computation and interpretation of entanglement entropy in this holographic model.
 Speaker: Mario Flory Material:
• Thursday, 16 April 2015
• 09:00 - 12:50 Morning session
• 09:00 Quantum quenches & holography 40'
We study quantum quenches in a holographic framework, where the quenches involve varying the coupling of a relevant operator in the boundary theory. The time dependence of the new coupling is characterized by a transition time and the observables exhibit a universal scaling behaviour when this timescale becomes the smallest scale in the problem. The same scaling behaviour is found for mass quenches in free field theories and we argue that, in fact, it will apply for any theory which flows from a ultraviolet fixed point.
 Speaker: Robert Myers Material:
• 09:40 Holographic entanglement entropy in excited states from 2d CFT 40'
I will consider the entanglement entropy in 2d conformal field theory in a class of excited states produced by the insertion of a heavy local operator. I will discuss the universal contribution from the stress tensor to the single interval entanglement entropy, and conjecture that this dominates the answer in theories with a large central charge and a sparse spectrum of low-dimension operators. The resulting entanglement entropy agrees precisely with holographic calculations in three-dimensional gravity. I will illustrate this in two examples: high-energy eigenstates of the Hamiltonian and local quenches.
 Speaker: Alice Bernamonti
• 10:20 Coffee break 30'
• 10:50 Holographic thermalization and AdS instability 30'
I will discuss recent developments in the study of AdS (in)stability and their relation to holographic thermalization.
 Speaker: Ben Craps Material:
• 11:20 Black brane steady states 30'
We follow the evolution of an asymptotically AdS black brane with a fixed temperature gradient at spatial infinity until a steady state is formed. The resulting energy density and energy flux of the steady state in the boundary theory are compared to a conjecture on the behavior of steady states in conformal field theories. Very good agreement is found.
 Speaker: Amos Yarom Material:
• 11:50 Chaos in the matrix model, and formation and evaporation of a black hole 30'
We study real-time evolution of a highly stringy regime of the BFSS matrix model by using a numerical method. We demonstrate that several important properties of a black hole, such as the fast scrambling and evaporation, can be seen, just by following classical time evolution of the matrix model.
• 12:20 Holographic topological entanglement entropy and ground state degeneracy 30'
Topological entanglement entropy, a measure of the long-ranged entanglement, is related to the degeneracy of the ground state on a higher genus surface. We construct a class of holographic models where such relation is similar to the one exhibited by Chern-Simons theory in a certain large N limit. Both the non-vanishing topological entanglement entropy and the ground state degeneracy in these holographic models are consequences of the topological Gauss-Bonnet term in the dual gravitational description.
 Speaker: Andrei Parnachev Material:
• 12:50 - 14:20 Lunch break
• 14:20 - 18:10 Afternoon session
• 14:20 Simulations of BH Collisions in AdS5 40'
In the context of gauge/gravity duality, it has been suggested that the far-from equilibrium strongly coupled dynamics encountered in ultrarelativistic heavy-ion collisions may be modeled as the collisions of black holes in asymptotic anti-de-Sitter spacetimes. I will present results from the evolution of spacetimes that describe the merger of asymptotically global AdS black holes in 5D with an SO(3) symmetry. The initial trapped regions are sourced by scalar field collapse and we are able to evolve through the ensuing black hole merger as well as subsequent ring-down. The boundary stress tensor corresponding to this evolution is found to correspond to hydrodynamics at late times, but not at early times. Implications and generalizations of this work and signatures that could be relevant to experimental observations at RHIC and the LHC will be discussed.
 Speaker: Paul Romatschke Material:
• 15:00 Equilibration rates in a strongly coupled nonconformal quark-gluon plasma 40'
We study of equilibration rates of strongly coupled quark-gluon plasmas in the absence of conformal symmetry. We primarily consider a supersymmetric mass deformation within N}=2^* gauge theory and use holography to compute quasinormal modes of a variety of scalar operators, as well as the energy-momentum tensor. In each case, the lowest quasinormal frequency, which provides an approximate upper bound on the thermalization time, is proportional to temperature, up to a pre-factor with only a mild temperature dependence. We find similar behaviour in other holographic plasmas, where the model contains an additional scale beyond the temperature. Hence, our study suggests that the thermalization time is generically set by the temperature, irrespective of any other scales, in strongly coupled gauge theories.
 Speaker: Alex Buchel Material:
• 15:40 A more realistic thermalization scenario in holography 30'
Holography has provided a brand new window on the thermalization of Yang-Mills plasmas. Compared to data from Relavistic Heavy Ion Collisions, holographic computations tend to (1) have a shorter thermalization time scale, (2) permit a linearized description in terms of quasinormal modes already at extremely early stages rather than close to the final configuration, (3) thermalize less from the IR up than one would infer from weakly coupled field theories. We will argue in particular that the holographic linearized quasinormal description is an artefact of the large N limit, and that 1/N corrections should make the system more realistic. We test this by introducing an additional decay of the quasinormal modes to each other. Our results show that this diminishes the three discordances between holographic thermalization and experiment.
• 16:10 Coffee break 30'
• 16:40 Holographic Kondo defects and universality in holographic superconductors with broken translation symmetry 30'
For a recently established holographic model of a magnetic impurity coupled to a strongly interacting system, we consider quantum quenches as well as the entanglement entropy. Both provide information about the size and formation of the Kondo cloud which screens the impurity. As a second topic, I will present recent results on universal behaviour in a family of holographic s-wave superconductors obtained by adding a scalar field to translation-breaking gravity backgrounds with Bianchi VII symmetry.
 Speaker: Johanna Erdmenger Material:
• 17:10 Holographic spin fluctuation and competition of two orders 30'  Speaker: Sang-Jin Sin Material:
• 17:40 A Monotonicity Theorem for Two-dimensional Boundaries and Defects 30'
I will propose a proof for a monotonicity theorem, or c-theorem, for a three-dimensional Conformal Field Theory (CFT) on a space with a boundary, and for a two-dimensional defect coupled to a higher-dimensional CFT. The proof is applicable only to renormalization group flows that are localized at the boundary or defect, such that the bulk theory remains conformal along the flow, and that preserve locality, unitarity, and Euclidean invariance along the defect. The method of proof is a generalization of Komargodski’s proof of Zamolodchikov’s c-theorem. The key ingredient is an external “dilaton” field introduced to match Weyl anomalies between the ultra-violet (UV) and infra-red (IR) fixed points. Unitarity of the dilaton’s effective action guarantees that a certain coefficient in the boundary/defect Weyl anomaly must take a value in the UV that is larger than (or equal to) the value in the IR.
 Speaker: Andrew O'Bannon Material:
• 20:30 - 23:30 Social Dinner
The social dinner will take place at 8:30 p.m. at Ristorante Palazzo Gaddi 
• Friday, 17 April 2015
• 09:00 - 12:50 Morning session
• 09:00 Effective actions for fluids from holography 40'
Effective actions based on scalar fields or Goldstone bosons are frequently used to describe fluids. The precise interpretation of such actions from a gravitational point of view has been somewhat unclear. In this talk I will describe a holographic interpretation of such effective actions and discuss the connection to other approaches to fluid/gravity duality.
 Speaker: Jan de Boer Material:
• 09:40 Entwinement and the emergence of spacetime 40'  Speaker: Vijay Balasubramanian
• 10:20 Coffee break 30'
• 10:50 Torsional Newton-Cartan geometry in Lifshitz holography and non-relativistic field theories 30'
I will discuss recent progress in understanding Lifshitz holography, including the appearance of torsional Newton-Cartan geometry on the boundary. The coupling of non-relativistic field theories to such a geometry will be cosnidered, along with the corresponding symmetry structure for the case of a flat Newton-Cartan background. We will show that, depending on the details of the action, such actions can have various degrees of global space-time symmetries ranging from Lifshitz to Schroedinger. On the holographic side, we show that the Lifshitz vacuum is the perfect dual of flat Newton-Cartan spacetime, exhibiting the same symmetries.
 Speaker: Niels Obers Material:
• 11:20 How far can we push the AdS/Ricci-flat correspondence? 30'
The AdS/RF correspondence connects classes of Ricci-flat spacetimes to asymptotically anti-de Sitter spacetimes, and thus endows these vacuum gravity solutions with a generalized conformal symmetry and a holographic structure, both inherited from AdS. The precise map requires however the dimensional reduction over a round sphere, and is therefore unsuitable to gain insights into asymptotically flat spacetimes, such as the Schwarzschild black hole. In this talk, I will explore the possibility of circumventing this limitation and to extend the correspondence to more general classes of spacetimes.
 Speaker: Marco Caldarelli Material:
• 11:50 AdS black hole thermodynamics with scalar hair 30'
I will discuss the thermodynamics of asymptotically AdS black holes with scalar hair whose mass lies in the window allowing mixed (multi-trace) boundary conditions. Such boundary conditions on the scalars require a careful definition of the asymptotic charges, but the first law and other thermodynamic properties continue to hold in their usual form.
• 12:20 From strange metals to black holes and back: effective theories of thermoelectric transport 30'
What can Gauge/Gravity duality teach us about Condensed Matter physics? While the search goes on for gravitational duals to strange metals and other strongly-coupled Condensed Matter systems, I'll discuss two specific examples where holographic computations have allowed us to formulate effective theories of thermoelectric transport, the existence of which does not rely on holography or long-lived Landau quasiparticles. One is a scaling theory of thermal quantum critical transport, the other a theory of 'hydrodynamics' without conserved momentum.
 Speaker: Blaise Gouteraux Material:
• 12:50 - 14:20 Lunch break
• 14:20 - 18:10 Afternoon session
• 14:20 Entanglement and differential entropy for massive flavors 40'
In this talk we will discuss entanglement entropy for massive flavors, from both holographic and field theory perspectives. We will describe efficient computational methods for the holographic entanglement entropy of brane systems, and we will show that the holographic entanglement entropy agrees precisely with field theory expectations. We will explain how to extract finite terms in the the entanglement entropy unambiguously and give physical interpretations to these finite contributions. Finally we will discuss the differential entropy for such systems, arguing that (in contrast to earlier work) the differential entropy does not capture global spacetime structure.
 Speaker: Marika Taylor Material:
• 15:00 Behind the geon horizon 40'
We explore the Papadodimas-Raju prescription for reconstructing the region behind the horizon of one-sided black holes in AdS/CFT in the case of the RP^2 geon - a simple, analytic example of a single-sided, asymptotically AdS_3 black hole, which corresponds to a pure CFT state that thermalises at late times. We show that in this specific example, the mirror operators involved in the reconstruction of the interior have a particularly simple form: the mirror of a single trace operator at late times is just the corresponding single trace operator at early times. We use some explicit examples to explore how changes in the state modify the geometry inside the horizon.
 Speaker: Monica Guica Material:
• 15:40 Position space analysis of the AdS (in)stability problem 30'
We investigate whether arbitrarily small perturbations in global AdS space are generically unstable and collapse into black holes on the time scale set by gravi- tational interactions. We argue that current evidence, combined with our analysis, strongly suggests that a set of nonzero measure in the space of initial conditions does not collapse on this time scale. On the other hand, existing results do not provide an equally strong indication whether the unstable solutions also form a set of nonzero mea- sure. We perform an analysis in position space to address this puzzle, and our formalism allows us to directly address the vanishing-amplitude limit. We show that gravitational self-interaction leads to tidal deformations which are equally likely to focus or defocus energy, and we sketch the phase diagram accordingly. We also clarify the connection between gravitational evolution in global AdS and holographic thermalization.
 Speaker: Matthew Lippert Material:
• 16:10 Coffee break 30'
• 16:40 A Simple Holographic Superconductor with Momentum Relaxation 30'  Speaker: Keun-Young Kim Material:
• 17:10 Spin Matrix theory as a model for the AdS/CFT correspondence 30'
We introduce a new type of quantum mechanical theory called Spin Matrix theory. It is a generalization of nearest-neighbor spin chain theories. We show that Spin Matrix theory arise from N=4 super Yang-Mills theory near certain zero-temperature critical points. We find that Spin Matrix theory contains a variety of phases that mimics that of the AdS/CFT correspondence, and hence gives a quantum mechanical model of the AdS/CFT correspondence. Finally, we suggest that Spin Matrix theory by itself can describe a Holographic correspondence. 
 Speaker: Troels Harmark Material:
Motivated by holographic stringy hadrons, I propose a model of stringy hadrons in four flat space-time dimensions. Mesons are rotating open strings with massive quarks" in their endpoints. Baryons are open strings with a quark on one end and a baryonic vertex and a di-quark on the other end. Glueballs are rotating folded closed strings.
A detailed fit of the model to  experimental data will be presented including extracting the best fit parameters for the string tension, intercept and endpoint masses. The issue of the identification  nature's gluballs" will be addressed.
I will discuss and report on  certain progress about  the yet unsolved problem of the quantization of rotating bosonic open ( with massive endpoints) and folded closed  strings in four dimensions.`