# Gravity and Other Fields Under the Volcano

Europe/Rome
Catania

#### Catania

Museo Diocesano Piazza Duomo, Via Etnea, 8 - 95121 Catania
, ,
Description

### One of the most pressing issues in modern physics is the quest for the physical laws describing our universe at very high energies.  Experimental data from collider physics and from primordial cosmology constrain our theoretical descriptions normally encoded in effective (quantum) field theories, which are low-energy models of a, yet unknown, fundamental theory.  In recent years the understanding of the ultraviolet completion of the standard model of particle physics has benefited from considerable developments.  Notably, extensions of particle physics models have been found to be asymptotically safe, a property which is also shared by gravity if treated as an ordinary field theory.  Significant progress to understand the fundamental nature of quantum spacetime has also come from other directions, both at the continuum level, as in the case of supersymmetric extensions, and in the discrete formulations, according to which the spacetime is an emergent concept.  The aim of this conference is to put together various experts on unification theories and quantum gravity approaches in order to discuss theoretical and phenomenological implications of these topics in different areas, such as particle physics, high energy astrophysics, Black Holes and Early Universe Cosmology.

Participants
• Alessandro Tronconi
• Alex Mitchell-Lister
• Alexander Kamenshchik
• Alfio Bonanno
• Andrea Trombettoni
• Astrid Eichhorn
• Augusto Sagnotti
• Benjamin Knorr
• Bertrand Delamotte
• Bianca Dittrich
• Carlo Pagani
• Carlos Nieto
• Chris Ripken
• Damiano Anselmi
• Daniel Litim
• Dario Benedetti
• Dario Zappala'
• Ergin Sezgin
• Fabio Scardigli
• Fabrizio Nesti
• Fiorella Burgio
• Gabriele, S.J. Gionti
• Georgios Kofinas
• Gian Paolo Vacca
• Giorgio Immirzi
• Hristu Culetu
• Jan M. Pawlowski
• Kevin Falls
• Kirill Krasnov
• Luca Griguolo
• Luca Zambelli
• Ludwik Dabrowski
• Manuel Reichert
• Marcello Baldo
• Martin Reuter
• Matthew Kellett
• Michele Lenzi
• Oleg Antipin
• Omar Zanusso
• Renate Loll
• Riccardo Ben Ali Zinati
• Roberto Percacci
• Saverio Lombardi
• Stefan Lippoldt
• Steffen Gielen
• Tereza Vardanyan
• Tim Morris
• Tommaso De Lorenzo
• Vasilios Zarikas
• Vincenzo Branchina
Secretariat
• Monday, 10 June
• 08:50 09:05
Registration 15m
• 09:05 09:15
Welcome from Directors (INFN , INAF) 10m
• 09:15 10:00
Resummation, renormalons and asymptotic safety 45m
Speaker: Oleg Antipin
• 10:00 10:45
Rethinking asymptotic freedom 45m

The renormalization-group flow of Higgs-Yukawa models with a non-Abelian gauge sector has been studied for several decades by adopting two simplifying assumptions: that the theory is perturbatively renormalizable and that all mass terms are negligible at high energies. Within this theoretical framework, total asymptotic freedom appears to be a rare phenomenon which severely constrains the matter content and the symmetry groups. We show how dropping the two above-mentioned assumptions allows to construct new large families of totally asymptotically free quantum field theories. The latter have strong predictive power and may thus find applications in physics beyond the standard model.

Speaker: Luca Zambelli
• 10:45 11:15
Coffee Break 30m
• 11:15 12:00
Stability Issues with Broken Supersymmetry and Some Clues for Early Cosmology 45m
Speaker: Augusto Sagnotti (PI)
• 12:00 12:45
Fakeons and quantum gravity 45m
Speaker: Damiano Anselmi (PI)
• 12:45 14:15
Lunch 1h 30m
• 14:15 15:00
Aspects of higher spin theories 45m

I will describe the salient features of higher spin theories as gauge theories based on infinite dimensional extension of (A)dS algebras, a la Vasiliev. The fully nonlinear equations of motion are formulated compactly on a product of spacetime with a noncommutative twistor space. I will highlight a powerful method for finding exact solutions of the theory which crucially employs the twistor space, and touch upon prospects for applications to cosmology.

Speaker: Ergin Sezgin
• 15:00 15:45
Metric-affine quantum gravity 45m
Speaker: Roberto Percacci
• 15:45 16:15
Coffee Break 30m
• 16:15 17:00
Massive Gravity 45m

I describe the efforts to implement a theory of massive graviton and how the request for a weakly coupled phase leads to the need to break not only general covariance, but also Lorentz symmetry. Hamiltonian analysis of the nonperturbative degrees of freedom, as well as cosmology and exact solutions generalizing the Schwarzschild one are described.

Speaker: Fabrizio Nesti (TS)
• 17:00 17:35
Analytic Coupling Structure of Large N_f (Super) QED and QCD 35m
Speaker: Manuel Reichert
• 17:35 18:10
Ultraviolet completion and predictivity from a minimal parameterization of Beyond-Standard-Model physics 35m

I will discuss the fate of the U(1) gauge coupling under the inclusion of vector-like fermions in the standard model. Then, motivated by results on quantum gravity contributions to the running of gauge and Yukawa couplings, I talk about the effect of simple but general corrections on the running of those couplings from the EW to large enough energy scales. One of our goals is to have an explanation for the pattern observed in the masses of the quark sector in the standard model, as well as the mixing angles.

Speaker: Carlos Nieto
• 18:10 18:15
Pausa 5m
• 18:15 18:29
2 minutes Poster presentations 14m
• Tuesday, 11 June
• 09:00 09:45
Background Independent Quantum Field Theory and Gravitating Vacuum Fluctuations 45m
Speaker: Martin Reuter
• 09:45 10:30
Perturbatively renormalizable quantum gravity 45m

The Wilsonian renormalization group (RG) requires Euclidean signature. The conformal factor of the metric then has a wrong-sign kinetic term, which has a profound effect on its RG properties. In particular around the Gaussian fixed point, it supports a Hilbert space of renormalizable interactions involving arbitrarily high powers of the gravitational fluctuations. These interactions are characterised by being exponentially suppressed for large field amplitude, perturbative in Newton's constant but non-perturbative in Planck's constant. By taking a limit to the boundary of the Hilbert space, diffeomorphism
invariance is recovered in the continuum quantum field theory. Thus the so-called conformal factor instability is the key that allows the construction of a genuine continuum
limit for quantum gravity.

Speaker: Tim Morris
• 10:30 11:00
Coffee Breakk 30m
• 11:00 11:45
Effective universality and unitarity in quantum gravity & the spectral function of the graviton 45m
Speaker: Jan Pawlowski
• 11:45 12:30
Fixed points of gauge theories and gravity 45m
Speaker: Daniel Litim
• 12:30 14:00
Lunch 1h 30m
• 14:00 14:45
Wilson loops and curvature in (quantum) gravity 45m
Speaker: Renate Loll
• 14:45 15:30
Towards a phenomenology of scale invariance 45m

Asymptotic safety, i.e., scale invariance in the ultraviolet, is a compelling proposal for the nature of fundamental interactions. Understanding its phenomenological consequences is a critical challenge, as any physical theory requires testing through confrontation with observations and experiments. In this talk I will discuss potential consequences of asymptotic safety for (Beyond) Standard Model physics as well as black holes.

Speaker: Astrid Eichhorn
• 15:30 16:00
Coffee Break 30m
• 16:00 16:45
Asymptotic safety and the dimension of the critical surface 45m
• 16:45 17:30
Geometry of the theory space and the functional renormalization group 45m

We consider the theory space as a manifold whose coordinates are given by the couplings appearing in the effective action. We discuss how to introduce connections on this theory space in the framework of the functional renormalization group (FRG). Finally, we discuss possible developments and limitations of this formalism and how to overcome such difficulties in the FRG setting.

Speaker: Carlo Pagani
• 17:30 18:15
Frame (In)equivalence in Quantum Field Theory and Cosmology 45m

I will discuss whether or not scalar-tensor theories in the Einstein and Jordan frames are equivalent once quantum corrections are taken into account. To understand this problem it is crucial to carefully define the path integral measure that arises in the quantization of the equivalent classical theories. Generically two measures will differ if the spacetime metrics in the two theories are related by a non-trivial conformal factor. Consequently this difference leads to a finite contribution to the effective action which distinguishes the two frames at the quantum level. This contribution is of particular relevance for classically scale invariant theories since quantising the theory in the Einstein frame is equivalent to a scale invariant quantisation procedure in the Jordan frame.

Speaker: Kevin Falls
• 20:00 23:30
Dinner 3h 30m
• Wednesday, 12 June
• 09:45 10:30
Gravitational Waves: a novel powerful tool to test fundamental theories 45m

The recent discoveries of gravitational waves (GWs)
from the LIGO and Virgo interferometers opened a new
era in GWs as well as multi-messenger astronomy, and offered new ways to test gravitational theories beyond Einstein's theory of General Relativity.
Very recently it has been also shown how nonperturbative quantum gravity (QG) can affect the GW luminosity distance associated with the long distance propagation of GWs, hence proposing a new test of QG theories through LIGO and LISA detection of merging events.

• 10:30 10:55
A Multi-Benefit Solution of Dark Energy problem based on the IR behavior of asymptotic safe gravity 25m

Infrared corrections that arise in some theoretical attempts to
understand Quantum Gravity may be the solution to one tantalizing problem of modern physics. Recently a novel Asymptotically Safe cosmology suggested a simple and attractive mechanism towards resolving naturally the structure
of dark energy and its associated cosmic coincidence problem. The novel idea is that the recent accelerated expansion of the universe happens due to infrared quantum gravity modifications at intermediate astrophysical scales galaxies or galaxy clusters. The reason is that structures of matter are associated with a non zero positive cosmological constant of quantum origin. In this context no extra unproven energy scales or fine-tuning are
used. Furthermore, this model was confronted with the most recent observational data from low-redshift probes. Measurements of the Hubble parameter, standard candles (Pantheon SnIa, Quasi-stellar objects), Baryonic Acoustic Oscillations (BAOs) and high redshift probes (CMB shift
parameters) were used to test the model. The overall likelihood analysis constrained the free parameters of the model. Moreover, it was tested against the concordance model (flat $\Lambda$CDM) utilizing a large family of information criteria. This Asymptotically Safe model proved to be statistically equivalent with $\Lambda$CDM, suggesting it as a very
interesting and realistic minimal solution to the problem of dark energy.

Speaker: Vasilios Zarikas
• 10:55 11:25
Coffee Break 30m
• 11:25 12:10
SO(7,7) structure of the SM fermions 45m

It has been suggested in the past (by several different authors) that the Standard Model gauge group can be combined with Lorentz group. If this is done, all fermions of a single generation of the SM receive the interpretation of components of a single spinor of a pseudo-orthogonal group Spin(p,q) of dimension p+q=14. There are only two possibilities that do not lead to the fermion doubling - Spin(11,3) and Spin(7,7). The former has in particular been studied by Roberto Percacci. This talk advocates the second option. We point out that there is some exceptional geometry related to the Weyl representation of Spin(7,7) (components of which are the SM fermions). In particular, we explain that a non-zero generic Weyl spinor of Spin(7,7) defines a metric in 7 dimensions. This suggests that there is some hidden geometric structure behind the pattern of the SM fermions.

Speaker: Kirill Krasnov
• 12:10 12:55
Covariance And Spectral Geometry of Spinor Fields 45m

All the fundamental matter particles are fermions and correspond
to spinor fields.
They arise as projective representation of the rotations
and (pseudo) orthogonal groups, and their installation on curved
space-times requires introducing of particular geometric structures.
I will discuss some of their surprising and nontrivial aspects
including the seldom discussed subtle issue of general covariance.
Another aspect of spinor fields I will survey
is the spectral geometry as described by the Dirac operator
which constitutes a crucial ingredient of a {\em spectral triple};
the appropriate concept for a passage to "quantum" spaces.

Speaker: Ludwik Dabrowski
• 12:55 14:25
Lunch 1h 30m
• 14:25 15:10
Surprises in the O(N) models or why might the standard large N analysis fail 45m

The O(N) models are probably the most studied field theories. Everything is supposed to be known about their symmetric and symmetry broken phases as well as their critical behavior. Many analytical methods were born here and it is the textbook example for both the $\epsilon=4-d$ and the
large-$N$ expansions. We nevertheless show that several
renormalization group fixed points of this model were not found by the usual methods. These new fixed points are relevant for the multicritical physics of the O(N) models.
We also show that the $N\to\infty$ limit was not
able to identify them because of an implicit analyticity prerequisite of this method that turns out to be wrong. The functional and nonperturbative renormalization group plays a key role to find them.

Speaker: Bertrand Delamotte
• 15:10 15:55
Holography for general boundaries 45m

I give a review of recent work on establishing holographic duals for quasi-local boundaries in 3D perturbative and non-perturbative gravity, as well as its extension to 4D gravity.
In particular I will show how holographic duals can be constructed as effective actions for geometric boundary observables. I will then connect this work with more standard holographic considerations at asymptotic AdS and flat boundaries.

Speaker: Bianca Dittrich
• 15:55 16:25
Coffee Break 30m
• 16:25 17:10
Gravity with more or less gauging 45m

General Relativity is conventionally formulated as a theory with gauge invariance under the diffeomorphism group of general coordinate transformations, but there are locally equivalent formulations in terms of either a larger (additional local conformal invariance) or smaller (only "special" diffeomorphisms) group of symmetries. Other formulations with the same number of gauge generators, but a different gauge algebra, also exist. We will discuss how one can relate these different formulations to each other, and illustrate various applications in which one may prefer one or another formalism. The talk is mostly based on arXiv:1805.11626.

Speaker: Steffen Gielen
• 17:10 17:55
Peculiarities of FRG-Quantum-Gravity 45m

In this talk I will point out some properties of general relativity, which are particularly important for the FRG. First I am going to consider the special structure of the gauge symmetry in gravity leading to a discussion of gauge invariance within asymptotic safety. Second I will highlight some consequences of boundaries in path integrals arising, e.g., when restricting the path integral to metrics of Euclidean signature.

Speaker: Stefan Lippoldt
• 17:55 18:05
Closing 10m