Critical properties of lattice gauge models

• Claudio Bonati (University of Pisa)

Critical phenomena in statistical models characterized by gauge symmetries present a richer phenomenology than in standard (i.e. non gauge invariant) statistical models. We discuss the main features of this phenomenology and introduce a possible classification of the different types of critical behaviors that can be expected. This classification is related to the nature of the QFT that encodes the critical behavior, which can for example be a standard LWG phi^4 theory, a gauge field theory, or involve nonlocal objects.

A gravitational collapse singularity theorem consistent with black hole evaporation

• Ettore Minguzzi (University of Pisa)

The global hyperbolicity assumption present in gravitational collapse singularity theorems is in tension with the quantum mechanical phenomenon of black hole evaporation. In this talk I show that the causality conditions in Penrose's theorem can be almost completely removed. As a result, it is possible to infer the formation of spacetime singularities even in absence of predictability and hence compatibly with quantum field theory and black hole evaporation.

Gauge dependence of momentum running in higher-derivative gravity

• Diego Buccio (Heidelberg University)

Running couplings were introduced in quantum field theory to preserve perturbativity in scattering amplitudes, despite the appearance of large logs of external momenta. It is commonly believed that such logarithms are directly related to UV divergencies in one-loop perturbation theory. However, this is not completely true in higher derivative theories: on the one hand, large logs can also emerge from UV finite loop integrals due to IR effects; on the other hand, some UV divergent diagrams do not depend on external momenta. We define a new set of beta functions for quadratic gravity based on the explicit computation of large logs of momenta and discuss their features concerning the asymptotic UV behaviour of the theory and their gauge dependence.

Primordial Regular Black Holes as all the Dark Matter

• Marco Calzà (University of Trento)

Primordial black holes (PBHs) are usually assumed to be described by the Schwarzschild or Kerr metrics, which, however, feature unwelcome singularities. We study the possibility that PBHs are nonsingular objects, considering phenomenological, regular tr- and non-tr-symmetric metric space-times. We characterize the evaporation of these PBHs and constrain their abundance from γ-ray observations. For most metrics, we find that constraints on $f_{pbh}$, the fraction of dark matter (DM) in the form of PBHs, weaken with respect to the Schwarzschild limits, because of modifications to the PBH temperature and graybody factors. Interestingly, we report that limist on the abundance may also tighten, providing an example from LQG.

Gravitational Contribution to Gauge and Yukawa beta functions

• Gabriele Giacometti (Istituto Nazionale di Fisica Nucleare)

The Asymptotic Safety scenario offers a clear way to describe Quantum Gravity that reaches completion in the ultraviolet and also links up with the matter content of the Standard Model. In this work we follow how the Renormalization Group changes when Quantum gravity couples to an SU(5) Grand Unified Theory. We check whether the dimensionless Newton constant g, the cosmological constant λ and the Yukawa coupling fy stay stable. We carry out a step-by-step numerical study of the fixed point structure. We look at the critical exponents θi plus at how gravity feeds into the matter beta functions fg and fy while the coarse graining scale parameter m changes. We test how well the truncation holds - varying the gauge fixing parameter. We uncover a non trivial interacting fixed point for the Yukawa coupling. This fixed point points to a way that gravity alone could set the values of fermion masses.

On the heat kernel of non-minimal second-order operators

• Dario Sauro (University of Jena)

We derive the local part of the trace of the second Seeley-DeWitt heat kernel coefficient for non-minimal second operators in a completely model-independent way. Afterwards, we provide two examples to show how our result can be applied in practical scenarios. We also present some aspects of the implementation in Mathematica of the model-independent result.

Gauge invariant quantum backreaction in U(1) axion inflation

• Davide Campanella Galanti

We study the quantum backreaction of a gauge field coupled to a pseudoscalar inflaton during slow-roll axion inflation. Using a fully gauge-invariant approach up to second order in perturbation theory, we include both inflaton and scalar metric fluctuations. We consider physical observers comoving with the inflaton field, allowing a consistent definition of the effective expansion rate. We find that the backreaction becomes significant early, rapidly moving the system out of the perturbative regime. The helicity of the gauge field dominates the initial dynamics, while the energy density contributes at later times. Overall, the backreaction prolongs inflation more than previously estimated when scalar metric perturbations are neglected.

The Cosmological Grassmannian

• Guilherme Leite Pimentel (Scuola Normale Superiore)

I will show how a Grassmannian turns out to be the natural kinematic space for describing correlation functions of massless spinning particles, in four dimensional (Anti)-de Sitter space. In this kinematic space, tree-level cosmological correlators factorize in a simple way and can be bootstrapped with rather ease, revealing some hidden beauty.

Plane waves and two-point functions in AdS

• Ugo Moschella (Istituto Nazionale di Fisica Nucleare)

I present some recent developments in AdS QFT: two new formulae for two-point functions and their application to compute some Feynman diagrams

Forecasting constraints on quintessential inflation

• Simony Santos Da Costa (University of Trento)

In this work, we investigate the constraining power of future CMB and galaxy surveys on models of quintessential inflation realized within the framework of α-attractors. We analyze how these future datasets will probe the parameter space of α-attractor quintessential inflation, specifically the inflationary potential parameters. Our results demonstrate that the synergy between CMB-S4, LiteBIRD, and Euclid can significantly tighten the bounds on the model parameters, achieving forecasted 1σ uncertainties of α = 2 ± 0.17, ns = 0.965 ± 0.0014, ln(1010As) = 3.0447 ± 0.0029 for the CMB+GCsp case. This level of sensitivity will enable us to discriminate between different realizations of quintessential inflation and test the attractor behavior characteristic of these models.

String axions and associated relics

• Nicole Righi (Scuola Normale Superiore)

String axions have been proposed as candidates for solving a number of puzzles in cosmology. In this talk, I will focus on axions as dark matter. After a review on how string axions can occur in our universe, I will provide a string theoretical explanation of dark matter as composed by ultralight axions. Based on the latest bounds, I will show how likely it is for dark matter to be composed of such particles and in which abundance, and I will provide predictions on the preferred ranges of masses and decay constants. On the contrary, requiring the axions to lie in a particular range of the parameter space imposes constraints on the UV theory and imply the existence of additional relics. Finally, I will discuss axions production at the end of inflation and the implications for the proposed cosmic axion background.

Light-Cone Approach to Cosmological Observables beyond Linear Order

• Pierre Béchaz (Istituto Nazionale di Fisica Nucleare)

With high precision data about to be released by large scale cosmological surveys, the development of higher order perturbative descriptions of cosmological observables is becoming increasingly important. The so-called Geodesic Light-Cone (GLC) coordinates are a physically motivated set of coordinates accounting for the fact that light-rays propagate on the past light-cone of an observer. They are a powerful tool to study both the primordial universe and the late-time one. In particular, regarding the latter, they allow for fully non-linear expressions for light-like cosmological observables. In this talk, I will first review how these coordinates are defined. Then, I will show how a cosmological perturbation theory up to the second order can be built on top of a background light-cone geometry. Within this new perturbative framework and adopting a fully gauge-invariant approach, higher order formulae for cosmological observables can be computed. I will focus on the observed redshift, the angular distance-redshift relation and the redshift drift. In particular, by means of the GLC gauge fixing, divergences arising in first- and second-order formulae can be eliminated in a totally model-independent way. Moreover, with this formalism one can obtain compact expressions for general relativistic effects, which play a crucial role in the study of Large Scale Structures as emergent features of primordial inflationary fluctuations.

Twisted period integrals in gravity and cosmology

• Giacomo Brunello (Scuola Normale Superiore)

Accurate modelling of gravitational-wave (GW) signals is essential for extracting masses, spins, and strong-field dynamics from current and future GW detectors. Within the observable-based (KMOC) formalism, gravitational radiation emitted in the scattering of two compact objects is encoded in the Fourier transform of five-point scattering amplitudes. In this talk, I present a novel analytic framework in which the Fourier transform to frequency space is combined directly with the loop integrals arising in the post-Minkowskian expansion, allowing scattering waveforms to be interpreted as twisted period integrals. These objects possess remarkable structural properties: they span finite-dimensional vector spaces and satisfy systems of differential and difference equations. This formulation enables the direct application of modern scattering-amplitude techniques in the frequency domain, including generalised unitarity and integration-by-parts identities with an exponential (Fourier) twist. As a result, gravitational waveforms can be systematically decomposed into a finite set of analytically computable master integrals. This yields the first fully analytic, velocity-exact two-body gravitational waveform and its power spectrum at second post-Minkowskian (one-loop) order. The framework naturally extends to the inclusion of spin effects and to higher post-Minkowskian orders.