Even from the very name, the international collaboration Event Horizon Telescope may suggest that the stellar objects hidden within the observed shadow are necessarily black holes safely covered inside a trapped region. However, on a purely classical level, one can exhibit models determining a shadow without a horizon. Recent speculations on possible alternative interpretations of the objects...

In a campaign to acquire astrometric data on the stars orbiting the compact source at the Galaxy center, Sgr~A*, the groups led by R. Genzel at Max Planck, and by A. Ghez at University of California, have used the most advanced observational techniques of European (GRAVITY instrument at VLT), and US based (Keck, Gemini North and Subaru), to reach an unprecedented precise determination of the...

We analyze the Brans-Dicke theory with a Gibbons-Hawking-York(GHY) boundary term and perform ADM decomposition both in Jordan and Einstein frames. For ω≠-3/2, we show that, at the Hamiltonian level, the Weyl (conformal) transformations from the Jordan to Einstein frames are not canonical transformations (in Hamiltonian sense). A set of canonical transformations is found. These are Anti-Gravity...

We examine the long-wavelength correlation functions of massive scalar fields in de Sitter space. For the theory with a quartic self-interaction, the two-point function is calculated up to two loops. Comparing our results with the Hartree-Fock approximation and with the stochastic approach shows that the former resums only the cactus type diagrams, whereas the latter contains the sunset...

Here we show that the standard 3D Gross–Pitaevskii equation (GPE) [1,2] for Bose-Einstein condensates (BECs) admits hydrodynamic interpretation in a general Riemannian metric. This is done by deriving the corresponding Euler and Navier-Stokes forms in full generality. We also show [3] that in this metric the momentum equation has a new term that is associated with local curvature and density...

Here we consider the hydrodynamic form of the momentum equation associated with the Gross-Pitaevskii equation (GPE) in general Riemannian metric [1] and show that, under particular steady state conditions, a new Einstein field equation can be determined in presence of negative scalar curvature. Since GPE vortex defects in Bose-Einstein condensates are useful, analogue models in cosmology, a...

The ESA Gaia mission measures directly positions and velocities of more than 1.5 billion stars to create the largest, most precise 6D kinematical map of the Milky Way (MW). High accurate measurements in space force fundamental astronomy to move from the "classical" paradigm, responding to Newton's gravity, to that of Einstein's General Relativity (GR). Then, GR must be at the very core of the...

After recalling its working tenets, the contribution introduces to the technological (including computational) challenges facing

the actual realization of a compact antenna in space that, complementary to current or future facilities, utilizes (sub)-micro-arcsecond

astrometry to estimate strength and pin-point direction of GWs, i.e., by using suitable natural star-like close pairs as...

As the sensitivity of existing ground-based detectors increases and new detectors appear, the number of gravitational-wave detections from compact binary mergers is also increasing. A low latency detection of these sources is primordial to increase the chances of observing counterparts, and an offline search allows for better exploitation of the data. In this talk, I will present how the...

I will review recent non-trivial tests of the AdS/CFT correspondence which provides a dual description of the 4D quantum gravity in terms of 3D Chern-Simons-matter superconformal field theories. After a general discussion, I will focus on BPS Wilson loops that represent one of the best playgrounds to match exact field theory results with dual gravity predictions.

We construct a new class of extension of General Relativity starting from the idea that the coupling between spacetime and matter is the key to understand dark phenomenology. We then focus on one of the simplest examples of such a class of theories which contains only one additional parameter dubbed "MEMe model". We show that this theory is able to offer a unified framework for dark energy and...

We present a simple quantum description of black holes and the late Universe in which the effective Schwarzschild-de Sitter spacetime geometry emerges from a coherent state of background gravitons. Once localised baryonic matter is added consistently, such quantum states are shown to describe regular black holes and to contain the necessary components to describe MoND phenomenology at galactic...

An exact form of the stress-energy tensor in quantum field theory (QFT) with a local equilibrium statistical operator would be a crucial ingredient of the semiclassical Einstein equation, with non-trivial quantum corrections to the equation of state. While a solution in a curved background is still unknown, much can be learned from solving related problems in flat space-time. In this talk, I...

We propose a model where, in the Einstein equations, the right-hand side is modified by the addition of a term proportional to the symmetrized partial contraction of the Ricci tensor with the energy-momentum tensor. Bearing in mind the existence of a natural length scale given by the Planck length, dimensional analysis shows that such a term yields a correction linear in hbar to the classical...

Spontaneous symmetry breaking is a transversal concept in modern physics, being pivotal for our understanding of mass generation in particle physics, topological defects formation in cosmology and the appearance of condensed phases of matter. I will discuss some recent results about the way symmetry breaking occurs for systems embedded in a curved background, when curvature acts as an...

We investigate the interplay between gravity and the quantum coherence present in the state of a pulse of light propagating in curved spacetime. We first introduce an operational way to distinguish between the overall shift in the pulse wavepacket and its genuine deformation after propagation.

We then apply our technique to quantum states of photons that are coherent in the frequency degree...

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...

In 2015, the two LIGO detectors revealed for the first time a gravitational wave from the coalescence of two black holes. Two years later Virgo joined LIGO in a worldwide network of advanced gravitational wave detectors, and the detection of a gravitational wave from the coalescence of a neutron binary star in 2017 opened the era of multi-messenger astronomy. Today, the LIGO-Virgo...

I will present the results of numerical relativity simulations of compact object binaries. I will focus in particular on the effects that magnetic fields can have in two different scenarios: binary neutron stars and supermassive black hole binaries. In the first one, magnetic fields can affect the post-merger evolution of the remnant and in particular its gravitational and electromagnetic...

Quantum noise is limiting the sensitivity of ground based gravitational wave detectors both at high and low frequency. Carlton Caves in 1980s proposed to introduce particular quantum states of lights, called vacuum squeezed states, from the output port of the detector to reduce this noise. In O3, the injection of frequency independent squeezing improved Virgo and LIGO sensitivities at high...

In this talk I will present a fully Bayesian parameter-estimation pipeline to measure the properties of inspiralling stellar-mass black hole binaries with LISA.

Our strategy (i) is based on the coherent analysis of the three noise-orthogonal LISA data streams, (ii) employs accurate and computationally efficient post-Newtonian waveforms –accounting for both spin-precession and orbital...

Precision measurements of the Earth rotation make it possible to investigate fundamental physics, as they contain general relativity terms, such as de Sitter and Lense Thirring, and can provide unique data to investigate possible Lorentz violations. These measurements require high sensitivity, usually parametrised as the fraction of the average Earth rotation rate; the limit to be reached to...

We will briefly present a detailed study of the methodology for correlating ‘‘dark sirens'' (compact binaries coalescences without electromagnetic counterpart) with galaxy catalogs. Several improvements on the current state of the art will be examined and applied to the published LIGO/Virgo gravitational wave (GW) detections, studying several sources of systematic errors. We will give the best...

Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. In calculations of spherically symmetric collapse, a Lagrangian relativistic hydrodynamical code is used to...

The introduction of a perfect fluid source in quantum cosmological models has permitted to write down the Wheeler De Witt equation in a form similar to the Schroedinger equation, by the introduction of a fiducial time. In the first part of the talk I introduce the formalism and discuss the nature of this fiducial time. In the second part I introduce the corresponding tomograms in order to...

In this talk we address the measurement concept and the main experimental challenges for LISA, the first space-based GW observatory, to be launched in 2034. The task of using laser interferometry to measure the GW tidal deformation of a constellation of free-falling test masses is discussed, both in the context of heritage from the preparatory single-spacecraft mission - LISA Pathfinder - and...

Gravity at short distances is still an open field for investigation. The measurement scheme we propose, with fluid source masses, overcomes some of the main limitations of torsion pendulum experiments. We overview the scientific motivations for such a search, outline the experimental apparatus and present a progress report on the activities, with the first experimental demonstration of the...

Einstein Telescope was conceived fifteen years ago, significantly before the first observations of gravitational waves. The concept was strongly characterized by the aim of constituting an European pole of development for a new observational branch of astrophysical science, ranging from fundamental interactions studies to cosmology. Many facts happened since that time. Given the quantity and...

Einstein Telescope is the European third-generation gravitational waves detector.

This new detector will detect GW sources in a Universe volume that is a thousand times bigger compared to the volume surveyed by the present detectors, reaching sources at cosmological distances. The promise, among the others, is to unveil new insight on compact objects like neutron stars and black holes, to...