Quantum gravity Vs unimodular quantum gravity
Strong gravity tests indicate that general relativity is a very accurate description of the classical dynamics of spacetime even at extreme regimes. Yet, the same dynamics can be described by "alternative" versions of general relativity such as unimodular gravity. In the quest for a quantum theory of the gravitational field, it is unclear if the quantization of such classically equivalent theories leads to the same physical predictions. In this talk, I will report on some recent results regarding this issue in the framework of continuum and perturbative quantum field theory.
The effective action of superrotation modes
Asymptotically flat spacetimes are invariant under an infinitedimensional symmetry group comprised of superrotations and supertranslations. These symmetries are spontaneously broken, leading to an infinite degeneracy of gravitational vacua in asymptotically flat spacetimes. Starting from an analysis of fourdimensional asymptotically flat gravity in first order formulation, I will describe how superrotation parametrization modes labelling distinct superrotation vacua are governed by an Alekseev–Shatashvili action on the celestial sphere.
Emergent cosmology from tensorial group field theories for quantum gravity
We introduce the basic elements of tensorial group field theories (TGFTs) for quantum gravity, emphasizing how they encode quantum geometry and their relation with canonical loop quantum gravity and spin foam models. Next, we discuss briefly the issue of continuum limit and how it could be understood in this framework.
Quadratic Gravity
An extension of general relativity (GR) obtained by adding local quadratic terms to the action will be considered. Such theory can be a viable UV completion of GR. The additional terms soften gravity above a certain energy scale and render gravity renormalizable. The presence of 4 derivatives implies via the Ostrogradsky theorem that the classical Hamiltonian is unbounded from below.
Evolving quantum state for black holes
A fundamental problem of quantum gravity is to understand the quantum evolution of black holes. While aspects of their evolution are understood asymptotically, a more detailed description of their evolving wavefunction can be provided. This gives a possible foundation for studying effects that unitarize this evolution, which in turn may provide important clues regarding the quantum nature of gravity.
Nonlocal cosmological models from infrared quantum gravity effects
The issue of whether quantum effects can affect gravity at cosmological distances still lacks a fundamental understanding, but there are indications of a nontrivial gravitational infrared dynamics. This possibility is appealing for building alternatives to the standard cosmological model and explaining the accelerated expansion of the Universe. In this talk I will discuss some large scale modifications of general relativity due to nonlocal terms, which are assumed to arise at the level of quantum effective action.
Matterdriven phase transition in lattice quantum gravity
The model of Causal Dynamical Triangulations (CDT) is a backgroundindependent and diffeomorphisminvariant approach to quantum gravity,
Getting hot without accelerating: vacuum thermal effects from conformal quantum mechanics
In this talk I will discuss how the generators of radial conformal symmetries in Minkowski spacetime are related to the generators of time evolution in conformal quantum mechanics. Within this correspondence I will show that in conformal quantum mechanics the state corresponding to the inertial vacuum for a conformally invariant field in Minkowski spacetime has the structure of a thermofield double. The latter is built from a bipartite "vacuum state" corresponding to the ground state of the generators of hyperbolic time evolution, which cover only a portion of the time domain.
Underground tests of Quantum Mechanics: Gravityrelated and CSL wave function collapse models
We are experimentally investigating possible departures from the standard quantum mechanics’ predictions at the Gran Sasso underground laboratory in Italy. In particular, with radiation detectors we are searching signals predicted by the collapse models (spontaneous emission of radiation) which were proposed to solve the “measurement problem” in quantum physics and signals coming from a possible violation of the Pauli Exclusion Principle.
Debate on Asymptotically Safe Quantum Gravity

John Donoghue University of Massachusetts Amherst

Roberto Percacci SISSA Scuola Internazionale Superiore di Studi Avanzati
Asymptotically safe gravity is one of the most conservative approaches to quantum gravity. It relies on the framework of quantum field theory and the Wilsonian renormalization group. Recently, questions and open issues have been discussed both within and outside its community.