Quantum gravity effects are generally expected to resolve the classical singularity of the Schwarzschild black hole. In this talk we present a general approach to construct effective models for nonsingular black holes and discuss their possible observational signatures.
Tests of the weak cosmic censorship conjecture examine the possibility of a breakdown of predictivity of the gravitational theory considered, by checking if curvature singularities are cloaked behind an event horizon at all times, during the time-evolution of an initial regular configuration. The conjecture has been a subject of intense scrutiny, but no convincing counter-example has been...
A quantum ghost that destabilizes the Schwarzschild solution, transforming it into a naked singularity, may seem like a physicist's worst nightmare. However, in this talk, we will argue that this scenario not only represents the natural evolution of a black hole under a conservative high-energy gravity framework, but is also a desirable outcome. There is much evidence that the Einstein-Hilbert...
Implementing strong curvature modifications to General Relativity (GR) may lead to the resolution of the spacetime singularity that arises at the end of gravitational collapse.
In the following, we consider the toy model of homogeneous dust collapse and explore the conditions under which such modified scenarios may produce a regular black hole.
Finally we showcase two illustrative examples:...
Regular black hole solutions typically come with an outer event horizon and an inner Cauchy horizon. In the case of the Reissner-Nordstrom geometry, the analysis based on the Ori model shows that the Cauchy horizon in unstable against perturbations, because of the mass-inflation effect. However, when such analysis is applied to regular black hole solutions, a richer picture emerges. We present...
This talk provides a conceptual analysis of the AMPS (firewall) and AMPSS paradoxes in black hole physics. We begin by cataloguing the various possible resolutions of the AMPS paradox through "causal structures", explaining that solutions like ER=EPR introduce non-local connections in semiclassical physics. Next, we address the AMPSS paradox, showing how resolutions tied to the program of...
The Galactic Center of the Milky Way can serve as a test bench to investigate physical phenomena at the edge of astrophysics and fundamental physics. As such, it offers a unique laboratory to probe General Relativity, modified theories of gravity, different paradigms of dark matter, and black hole mimickers. I will provide a general overview of the results achieved in recent years, emphasizing...
In this talk we consider the Oppenheimer-Snyder (OS) gravitational collapse in the general framework of scale-dependent gravity. Recent investigations show that a spherically symmetric solution of asymptotically safe gravity, when considered for a negative ω-parameter (so, properly speaking, in scale-dependent gravity), develops a singularity at a finite non-zero radial coordinate. The inner...
We describe a recently developed tool which enables a description
of spacetime as a manifold with a Lorentz-invariant limit length
built-in. This is accomplished in terms of quantities depending
on two spacetime events (bitensors) and looking at two-point function,
all this being well suited to embody nonlocality in the small scale.
What one obtains is a metric bitensor (called...
According to the asymptotically safe gravity, black holes can have characteristics different from those described according to general relativity. Particularly, they are more compact, with a smaller event horizon, which in turn affects the other quantities dependent on it, like the photon ring and the size of the innermost stable circular orbit. We decided to test the latter by searching in...
The literature is flourishing in exotic and theoretical
black hole solutions realized in the framework of general relativity
or modified gravity theories to cure the singularity affecting the
vacuum solutions of general relativity. On the other hand, the
Schwarzschild solution is the standard lore when computing constraints
on primordial black hole abundance arising from the isotropic...
Cosmic birefringence is a rotation of the polarization plane of photons coming from sources of astrophysical and cosmological origin. We discuss the imprints of a cosmological pseudoscalar field on Cosmic Microwave Background (CMB) propagation. Phenomenological or theoretically motivated redshift dependence of the pseudoscalar fields - such as axionlike dark matter, quintessence, or early dark...
Fundamental scale invariance was proposed long ago as a new theoretical principle beyond renormalizability. Besides its highly predictive power, a scale-invariant formulation of gravity could provide a natural explanation for the long-standing hierarchy problem and interesting applications in cosmology.
We present a globally scale-invariant model of gravity and study its cosmological...
I elaborate on the vector space structures of Euler-Mellin-Feynman Integrals,
emerging from the application of Intersection Theory of (twisted) De Rahm Co-homology,
and discuss the crucial role of the intersection numbers as fundamental mathematical quantities,
ruling linear relations (integration-by-parts identities or contiguity relations, differential and difference equations),
as...
We consider a theory of a massive scalar field in de Sitter spacetime. Through the Yang-Feldman-type equation, the one-, two-, and three-loop quantum corrections for the long-wavelength modes' two-point and four-point correlation functions have been calculated. The corresponding massive perturbative series being summed rids of secular effects. In contrast to the standard theory of a massive...
I present a general approach to de Sitter and anti de Sitter Quantum Field Theory based on the analyticity properties of the correlation functions which are closely similar to the ones which are equivalent to the positivity of the spectrum of the hamiltonian in every Lorentz frame Minkowski QFT (that is, the spectral condition). In this context I present an important family of plane waves well...
Asymptotic safety is a powerful mechanism for obtaining a consistent and predictive quantum field theory beyond the realm of perturbation theory. It hinges on an interacting fixed point of the Wilsonian renormalization group flow, which controls the microscopic dynamics. Connecting the fixed point to observations requires constructing the set of effective actions compatible with this...
We construct effective spacetime geometries by self consistently deforming the classical Schwarzschild-de Sitter solution. This has been done in the context of the Functional Renormalization Group Asymptotic Safe program by exploring how quantum modifications induced by the running of the Newton and Cosmological constants impact the infrared and ultraviolet regimes of the modified...
We evaluate the quantum backreaction due to a gauge field coupled to a pseudo scalar field driving a slow-roll inflationary stage, the so-called axion inflation. The backreaction is evaluated for the first time using a gauge invariant approach, going to second order in perturbation theory and considering inflaton fluctuations as well as scalar perturbations of the metric. Within our gauge...
Certain types of large-N gauge theories coupled to matter offer interacting UV fixed points that are under strict perturbative control, beyond the paradigm of asymptotic freedom. In this work, we derive and investigate functional RG equations for the quantum effective potential of the theory to leading order in a derivative expansion. We thereby find the RG flows, fixed points, and scaling...
It has been known for a long time, since the seminal works of Fradkin and Tseytlin as well as Taylor and Veneziano, that the calculation of the (euclidean) effective action in quantum gravity gives rise to quartic and quadratic UV-sensitive contributions (Planck scale) to the vacuum energy. The comparison of this result to the measured value of the vacuum energy, that is inferred from the...
It is largely known that the calculation of the (euclidean) effective action in quantum gravity is plagued by the appearance of quartic and quadratic UV-sensitive contributions to the vacuum energy. However, it has been recently shown in the Einstein-Hilbert truncation of pure gravity that a careful treatment of the measure in the path integral reveals the disappearance of these problematic...
In this talk we will introduce and perform ADM analysis for spherically symmetric solution of General Relativity. We will discuss with particular care the problem of the boundary terms to be introduced in the general case of spherical symmetry. We will derive the Hamiltonian equations of motion for Brans-Dicke theory, with spherical symmetry, stressing the importance of the boundary terms. We...
When the Higgs potential or the vacuum energy are derived in the framework of higher dimensional effective field theories on a multiply connected spacetime with compact dimensions and non-trivial boundary conditions (as in the case of the Scherk-Schwarz SUSY breaking), the usual calculations lead to the conclusion that these quantities are naturally UV-insensitive. By means of a thorough...
I will present examples of substructures of the Weyl group of transformations of the metric and discuss the physical properties of theories invariant under such symmetries.
Using cohomological methods, we identify both trivial and nontrivial contributions to the conformal anomaly in the presence of vectorial torsion in d = 2, 4 dimensions. In both cases, our analysis considers two scenarios: one in which the torsion vector transforms in an affine way, i.e., it is a gauge potential for Weyl transformations, and the other in which it is invariant under the Weyl...
When the AdS/CFT duality is used to describe strongly interacting condensed matter system it is referred to as AdS/CMT. In this talk I will consider rotational holographic transport in strongly coupled 2+1 dimensional systems, from the point of view of 3+1 dimensional gravity in anti de-Sitter background. We consider the moment of inertia
$ 𝐼 $ as a kind of transport coefficient, identified...
