In this talk I discuss a method to study amplitudes in AdS in the context of the AdS/CFT correspondence. In particular I will discuss how to study loop amplitudes by using the holographic CFT counterpart.
The detection of gravitational waves in 2015, thanks to the LIGO and Virgo interferometers, opened a new window on our Universe. The discoveries during the first three observing runs already had an extraordinary impact on both astrophysics, cosmology, and fundamental physics.
The GW community is now looking at the next long–prepared step: ‘third–generation’ detectors. Thanks to an increase...
In this talk, we delve into the application of the covariant phase space formalism to the study of conservation laws in General Relativity. Our focus is twofold: firstly, we demonstrate the association of the Carter constant with a genuine conserved Noether charge, utilizing the powerful tool provided by the covariant phase space. Secondly, we explore the dependence of the construction of...
In this talk I present some new results in the program of formulating Quantum Cosmology in a tomographic representation. In particularI I show new solutions of the Wheeler-De Witt equation recently obtained together with the correspondent tomograms.
Agency (ASI) that aims to provide Fundamental Physics measurements with the Galileo-FOC constellation of the Global Navigation Satellites System (GNSS). The measurements concern both the analysis of satellite orbits and of their atomic-clocks data. A new accurate analysis of the satellites onboard atomic-clocks can lead to the following significant results: i) measuring the gravitational...
Black-hole binary spin precession admits equilibrium solutions corresponding to systems with (anti-) aligned spins. Among these, binaries in the up-down configuration, where the spin of the heavier (lighter) black hole is co- (counter-) aligned with the orbital angular momentum, might be unstable to small perturbations of the spin directions. The occurrence of the up-down instability leads to...
Generalized Quasitopological Gravities (GQTGs) are higher-order extensions of Einstein gravity in D dimensions satisfying a number of interesting properties, such as possessing second-order linearized equations of motion on top of maximally symmetric backgrounds, admitting non-hairy generalizations of the Schwarzschild-Tangherlini black hole which are characterized by a single metric function...
A longstanding issue is the equivalence between the Jordan and the Einstein frames. It is believed, but not completely proved, that the cosmological physical observables are the same in the two frames. Our aim is to tackle this problem from the perspective of the Hamiltonian formalism. For this reason, we will perform the Hamiltonian analysis of the Brans-Dicke theory with Gibbons-Hawking-York...
Understanding the dynamics of binary black holes is crucial to extract information from gravitational-wave data. By now, a consistent amount of effort has been put into exploring the phenomenology of black-hole binaries in the Post-Newtonian regime that evolve on quasi-circular orbits and undergo spin precession. We present substantial advances in this area using a multi-timescale approach to...
This work investigates, as a first step, the four branches of BMS
transformations, motivated by the classification into elliptic, parabolic,
hyperbolic and loxodromic proposed a few years ago in the literature. We
first prove that to each normal elliptic transformation of the complex
variable z used in the metric for cuts of null infinity, there is a
corresponding BMS supertranslation. We...
The discovery of the Hulse Taylor pulsar gave indirect evidence of gravitational waves, but recent groundbreaking direct detection of gravitational waves by LIGO-VIRGO collaboration opened a new window to look at the celestial entities and cosmos. In this work we focus on exploring the impact of local anisotropic pressure on the quasinormal modes of neutron stars in the framework of general...
There have been some recent claims about the impact of general relativistic corrections on the dynamics of galaxies, with possible implications for their dark matter content. We examine and analyze the proposed models to discuss their reliability and limitations. Then, we focus on the properties of an exact solution of Einstein's equations describing a self-gravitating system, made of dust,...
General relativistic models of disc galaxies can provide non negligible corrections with respect the Newtonian description, for the rotation speeds and their relationship to the required gravitational mass. This result can be counterintuitive, for an object with sub-relativistic speeds such as a galaxy; but General Relativity (GR) does not only provide higher order, post-Newtonian corrections...
Detecting and coherently characterizing thousands of gravitational-wave signals is a core data-analysis challenge for the Laser Interferometer Space Antenna (LISA).Transient artifacts, or “glitches”, with disparate morphologies are expected to be present in the data, potentially affecting the scientific return of the mission. We present the first joint reconstruction of short-lived...
Stochastic gravitational wave backgrounds (SGWBs) are, to date, yet to be unequivocally observed. At the 𝑛𝐻𝑧 frequencies, tentative evidence for the observation of such signals has been recently reported.
In this talk, I will focus on prospects for the detection of SGWBs of astrophysical origin in the 10−4𝐻𝑧−103𝐻𝑧 frequency range.
I will show how recent progress in statistics and...
In modern cosmology there is an agreement that the seeds of structure formations reside in the quantum fluctuation of the geometry in the early universe, but there is no agreement about how these could be derived from a quantum theory of gravity. In this talk I present a proposal based on the covariant formulation of Loop Quantum Gravity. I describe how to define a wavefunction of the universe...
Fundamental scale invariance has been proposed 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 quadratic gravity and study its solutions in a...
We study the effects of a spatially homogenous magnetic field in Bianchi-I cosmological models. In particular, we review the case of a pure magnetic field and two models with dust and a massless scalar field (stiff matter), respectively. For all these cases, we analyse the approach to the singularity in some details and comment about the issue of the singularity crossing.
The standard model of cosmology, known as the ΛCDM model, is based on the Friedmann-Lemaître-Robertson-Walker (FLRW) class of models. It successfully describes the energy composition of the universe, with 68.3% attributed to Dark Energy, 26.8% to Dark Matter, and 4.9% to Ordinary Matter. However, it leaves us with the challenge of understanding the nature of the Dark Universe. The model...
The grand canonical ensemble of a d-dimensional
Reissner-Nordström black hole space in a cavity is analyzed through
the Euclidean path integral approach. The partition function of the
ensemble is given in terms of the fixed temperature and fixed electric
potential at the boundary of the cavity. One performs the zero loop
approximation, i.e., only the contribution of the solutions which...
I will review recent progress on gluing methods for constructing solutions of the Einstein equations, and other progress in mathematical general relativity
Pulsars are highly-magnetized, rapidly-rotating neutron stars that emit beams of radio waves from their magnetic poles. Due to the misalignment of the magnetic and rotation axes of the pulsar, our radio telescopes on Earth can detect a pulse for each rotation of the pulsar as in the ‘lighthouse effect’. Monitoring those pulses and their arrival times at radio telescopes is called “pulsar...
We investigate different extended scalar-tensor theories of gravity. Particularly, we study the theory in the Jordan frame with different non-minimal coupling, with a standard and non-standard kinetic term, and the impact of a cubic interaction term. The nonminimally coupled scalar field, regulating the gravitational strength, moves around recombination because of its coupling to pressureless...
After a brief description of what is a traversable wormhole we describe the connection between traversability and the Casimir effect. With the help of an equation of state we also discuss different form of solutions generated by the Casimir source. Yukawa deformations and the addition of an electromagnetic field to the original energy density are also discussed.
The first part of this contribution highlights the main results of the ERC project PROTEUS with regard to the conceptual difficulties encountered in current quantum gravity approaches. The second part of the talk is devoted to the discussion of more recent work on the foundations of quantum gravity with emphasis on their impact on the philosophical understanding of space, time and causal...
I will present the second data release of the European Pulsar Timing Array (EPTA), containing high-precision pulsar timing data for 25 millisecond pulsars collected with five of the largest radio telescopes in Europe as well as the Large European Array for Pulsars. This dataset forms the basis for the gravitational wave searches carried out by the EPTA. I will also present results from the...
The accretion of dark matter around the black hole could lead to the formation of surrounding halo. Such a dark matter dressed black hole can leave characteristic imprints in the observations including gamma-ray, gravitational lensing and gravitational waves. In this talk, I will talk several observational phenomena on the black hole with dark matter dress.
Quantum properties of spacetime can affect the evolution of quantum systems. We discuss this in a noncommutative spacetime setting, showing that the standard Liouville-von Neumann equation is replaced by a Lindblad equation. This leads to a decoherence mechanism by which pure states can evolve into mixed states. The decoherence time for the evolution of a free particle is used to show that the...
I will present the general formalism for including resistive dissipation and mean-field dynamo amplification of magnetic fields in the set of GRMHD equations, needed to simulate numerically the relativistic plasmas in the environment of compact objects. A selection of applications will be discussed, from the exponential growth and saturation of magnetic fields in thick tori around black holes...
Non-Lorentzian kinematical symmetries, especially the ones corresponding to the Galilei or Carroll relativistic limits (i.e., the speed of light taken to infinity or to zero), are nowadays the subject of vigorous investigations. This also concerns (quantum) deformations of such symmetries, described in the formalism of Lie bialgebras and Hopf algebras. The case of 2+1-dimensional spacetime is...
Quantum gravity is expected to introduce quantum aspects into the description of reference frames. Here we set the stage for exploring how quantum gravity induced deformations of classical symmetries could modify the transformation laws among reference frames in an effective regime. We invoke the quantum group 𝑆𝑈𝑞(2) as a description of deformed spatial rotations and interpret states of a...
I present a doubly special relativistic model inspired from the k-lightlike non-commutative spacetime framework. A kinematical IR/UV mixing mechanism emerges naturally from the deformed energy-momentum dispersion relation, when considering particles with very small speeds. Thus, this model is suited for studying Planck-scale corrections to atom interferometry experiments.
EPTA has been taking data for 25 years and has now uncovered the first hint of a common signal in the data. I will discuss what are the consequences on this results for the astrophysics of supermassive black hole binary, processes in the early universe and specific models of dark matter.
GRB (gamma-ray-burst) neutrinos are excellent probes for testing quantum-gravity-induced in-vacuo dispersion. In this scenario, inspired by quantum gravity research and associated with Lorentz Invariance Violation (LIV), empty quantum spacetime behaves like a dispersive medium affecting the propagation of ultrarelativistic particles, whose speed is affected by energy-dependent Planck-scale...
The axially symmetric stationary gravitational perturbations of Kerr black hole are analyzed (a) within the framework of the Debye potentials as well as (b) a perturbations of Kerr black hole within the Weyl\,--\,Lewis\,--\,Papapetrou class of metrics. We find the exact explicit calibration transformation which is needed to connect the metric perturbations in this approach. We also provide the...
The presentation introduces the growing family of the relativistic binary pulsars, highlighting some of the most recent intriguing outcomes resulting from the observations of these systems. In particular the focus will be on the last news from the investigation of the double-pulsar binary PSR J0737-3039. Finally, the perspectives from continuing the monitoring of these systems with present and...
Perturbation theory of vacuum spherically symmetric spacetimes is a crucial tool for understanding the dynamics of black hole (BH) perturbations as well as BH scattering phenomena. Since the pioneering work of Regge and Wheeler it is known that the equations for the perturbations can be decoupled in terms of (gauge-invariant) master functions that satisfy 1 + 1 wave equations. However, while...
There is growing evidence that Hořava gravity may be a viable quantum theory of gravity. It is thus legitimate to expect that gravitational collapse in the full, non-projectable version of the theory should result in geometries that are free of spacetime singularities. Previous analyses have shown that such geometries must belong to one of the following classes: simply connected regular black...
The stochastic gravitational wave background (SGWB) originates from numerous faint gravitational wave (GW) signals arising from coalescing compact binary objects. Based on the currently estimated merger rate, where the binary merger events are Poisson-distributed at any instance, the SGWB signal is expected to originate from non-overlapping GW signals. Current efforts to detect this signal...
Primordial black holes (PBHs) could have been formed in the very early Universe from large amplitude perturbations of the metric. Their formation is naturally enhanced during the quark-hadron phase transition, because of the softening of the equation of state: at a scale between 1 and 3 solar masses, the threshold is reduced of about 10% with a corresponding abundance of PBHs significantly...
This presentation delves into the study of 'hairy' black holes within the framework of Einstein scalar Maxwell gravity and Einstein scalar Gauss-Bonnet theories, with a focus on revealing new scalarized black hole solutions. We revisit established scalarization phenomena and venture into new solution territories, particularly highlighting the blend of linear and non-linear scalarization in...
Dark energy (DE) typically violates the same energy conditions that imply cosmological singularities, hence a DE that dominates at high energy can produce a singularity-free cosmology. If the DE conservation equation admits a high-energy fixed point, this represents an unstable de Sitter vacuum: for flat and open FLRW models this de Sitter state represents the past attractors for what then is...
As was shown by Ellis in gr-qc/0411096, one can establish a correspondence between the Schwarzschild metric and a particular Natario warp drive metric, making it possible for a warp drive spaceship to cross the black hole horizon. We generalize this result to Morris-Thorne wormholes and demonstrate that wormholes without horizons can be mapped to a different "quasi-Natario" class of metrics...
Adopting geometric-optics approximations in black hole spacetimes enables the construction of a mapping between black hole images and eikonal black hole quasinormal modes (QNMs). More explicitly, the real part and imaginary part of the QNM frequencies correspond to the ring size and the detailed ring structure of the image, respectively. This correspondence may be violated when going beyond...
We investigate possible manifolds characterizing traversable wormholes under the existence of a scalar field that is minimally coupled to gravity and has a kinetic and a potential energy. The feature of traversability requires the violation of the null energy condition followed by the existence of an exotic matter providing a negative energy density to the system. For this reason, we use a...
New physics beyond general relativity can modify image features of black holes and increase the separation between photon rings. For horizonless objects, new physics can generate a set of inner photon rings. Both cases motivate the exploration of synthetic images consisting of two rings. The talk will be focused on assessing the detectability of these features using closure quantities, with...
The Oppenheimer-Snyder model is the prototypical example of black hole formation by gravitational collapse. It predicts that a black hole horizon is formed once a star collapses to within its own Schwarzschild radius. After that, the collapsing matter reaches Planckian densities in a short proper time. What happens next is outside the reach of general relativity, as it involves the quantum...
Testing the strong gravity regime of general relativity is a primary goal of gravitational wave detectors. While it is expected that corrections to GR are small and unlikely to be identified with individual events, third generation GW detectors will allow to detect tens-of-thousands of events per year. Therefore, they will pave the way to precision tests by carefully stacking all the detected...
Black holes in General Relativity are famously characterized by two "hairs" only, the mass and the spin of the Kerr spacetime. Theories extending General Relativity, however, allow in principle for additional black hole charges, which will generally modify the multipole structure of the Kerr solution. Here, we show that gravitational wave observations of the post-merger ringdown signal from...
We employ Ehlers transformations, Lie point symmetries of the Einstein field equations, to efficiently endorse accelerating metrics with a nontrivial NUT charge. Under this context, we begin by re-deriving the known C-metric NUT spacetime described by Chng, Mann, and Stelea in a straightforward manner, and in the new form of the solution introduced by Podolský and Vrátný. Next, we construct...
In modified theories of gravity, the potentials appearing in the Schrödinger-like equations that describe perturbations of non-rotating black holes are also modified. In this talk, we ask how such modifications can be constrained with future, high-precision measurements of quasi-normal modes. We use a perturbative framework that allows one to map modifications of the effective potential, in...
The notion of particles is ambiguous in curved spacetimes. This often makes it difficult to explicitly picture the process of Hawking radiation in terms of pair creation of particles (one going to infinity as Hawking radiation and the other falling into the singularity).
I will show how such a difficulty can be circumvented in the case of near extremal black holes in 4d for scale invariant...
Recently, the search for departures from the symmetries of General Relativity has received significant attention in the literature. In this talk, I outline the techniques for probing the nature of spacetime symmetries using the generation stage of gravitational waves. By using a generic effective-field theory, I show our solution scheme of the modified Einstein equations and I write down the...
It's a well-known fact that Lorentz Violating (LV) theories of gravity, such as Horava-Lifshitz gravity, highlight possibility of a renormalizable, non-Lorentz-invariant UV completion of General Relativity (GR).
On the phenomenological side, the breaking of Local Lorentz Invariance gives a different notion of causality, for which the LV-Black Hole solutions assume a different internal...
The second postulate of special relativity states that the speed of light in vacuum is independent of the emitter's motion. The test of this postulate so far remains unexplored for gravitational radiation. We analyzed data from the LIGO-Virgo detectors to test this postulate within the ambit of emission models, where the speed of gravitational waves emitted by a source moving with a velocity 𝑣...
It is well known that the response of a black hole (BH) to an external perturbation consists in a series of damped sinusoids, dictated by complex frequencies called quasi-normal modes (QNMs). Massive fields also admit a different family of solutions called quasi-bound states (QBSs). Both families of modes dissipate energy at the BH horizon, and QNMs also radiate at infinity. This dissipation...
Superradiant scattering provides a interesting way of extracting energy from a rotating black hole by means of amplification of low-frequency electromagnetic (EM) radiation. If plasma in the accretion disk prevents the outgoing radiation from escaping to infinity, this process can happen repeatedly, triggering an instability that can lead to the appearance of bursts.
However, investigating...
Both Einstein's equations and the field equations of a modified theory of gravity can be derived as equations of state from purely thermodynamical considerations, leading to the identification of GR with an equilibrium state of gravity and modified gravity with a non-equilibrium one. This breakthrough made the relationship between gravity and thermodynamics even more intriguing. I will present...
We study how self gravitation of quantum systems affects the quantum coherence present in their state. Spatial superpositions of static, large, heavy systems tend to rapidly lose coherence, whereas light or massless particles are unaffected. Furthermore, large and heavy objects also rapidly localize into a single classical position. The ratio of the characteristic size of the system and its...
The geodynamic satellites LAGEOS (NASA, 1976), LAGEOS II (ASI/NASA, 1992) and LARES (ASI, 2012) were taken as test masses and their motions were carefully studied and compared with that of a time-like geodesic of General Relativity (GR). This allowed to obtain a series of significant results in the study of the gravitational interaction in the so-called weak-field and slow-motion (WFSM) limit...
MICROSCOPE’s final results report no violation of the Weak Equivalence Principle (Universalityof Free Fall) for Pt and Ti test masses quantified by an E ̈otv ̈os parameter η∼10−15, an improvementby about two orders of magnitude over the best ground tests. The measurement is limited byrandom noise with 1ν√ frequency dependence attributed to thermal noise from internal dampingoccurring in the...
Close hyperbolic encounters of black holes (BHs) generate certain Burst With Memory (BWM) events in the frequency windows of the operational, planned, and proposed gravitational wave (GW) observatories. We provide details of our HyperbolicTD & GW_hyp packages that should allow both LIGO-Virgo-KAGRA (LVK) and Pulsar Timing Array (PTA) consortia to search for such BWM events in their respective...
Black holes can be simulated by water in a tank or in general in analogue gravity models known as dumb holes. If one simulates the Hawking radiation in these models finds that the loss of information is equal to the loss of the momentum of the fluid over the dumb hole horizon. However, due to the steadiness of the horizon one expects that there is a missing momentum over the horizon. By...
It is well-known that the (1+1) dimensional Schwarzschild and spatially flat FLRW spacetimes are conformally flat. This work examines entanglement harvesting from the conformal field vacuums in these spacetimes between two Unruh-DeWitt detectors, moving along outgoing null trajectories. In (1+1) dimensional Schwarzschild spacetime, we considered the Boulware and Unruh vacua for our...
