Now that gravitational waves from compact binary coalescences have been successfully detected by the global LIGO-Virgo network, a key challenge is to improve the detector sensitivity in order to detect more transient sources — weaker or located further away. The detectors' sensitivity can be enhanced by increasing the laser power travelling within the arm cavities, for it reduces the effect of...

I will present few initial steps towards a new general relativistic magneto hydrodynamic (GRMHD) code devoted to the study of compact binary mergers with finite temperature equations of state and neutrino emission. Numerical modeling of neutron stars binaries (NS-NS), black holes binaries (BH-BH) and neutron star black hole binaries (NS-BH) has now become one of the most important fields of...

One fruitful approach to quantum gravity has been the framework of Causal Dynamical Triangulations (CDT). This path integral approach describes space-time in a nonperturbative and background-independent manner. The Planckian regime is characterized by wild and highly non-classical geometries and general relativity is recovered as an effective theory in the IR limit.

An important question is...

Constraining the equation of state (EoS) of cold dense matter in neutron stars (NS) is a major science goal for observing programmes conducted with X-ray,

radio, and gravitational wave telescopes. In this talk we demonstrate how to combine gravitational-wave and electromagnetic observations in order to solve

the relativistic inverse stellar problem, i.e. to reconstruct the main features of...

The second LIGO-Virgo observational witnessed the birth of gravitational-wave multi-messenger astronomy. The first ever gravitational-wave (GW) detection from the coalescence of two neutron stars, GW170817, associated to its gamma-ray counterpart, GRB 170817A, as well as its optical, X-ray and radio counterparts (AT 2017gfo).

In this talk, we will describe the O2 low-latency program of the...

Recently, two simple criteria were proposed to assess if vacua emerging from an effective scalar field theory are part of the string "landscape" or "swampland". The former are the vacua that emerge from string compactifications; the latter are not obtained by any such compactification and hence may not survive in a UV completed theory of gravity. So far, these criteria have been applied to...

The most accurate semi-analytical models for gravitational wave models for compact binaries are based on the effective-one-body (EOB) approach and calibrated to numerical relativity (NR) simulations. These models are however too slow to be used in parameter estimation runs, when $\sim 10^7$ waveforms have to be generated. This has prompted the construction of surrogate models, based on the...

Wave-function collapse following a measurement process is a longstanding controversial issue of quantum physics. It introduces an element of strong non-linearity and irreversibility in an otherwise unitary and reversible dynamics. Several proposals of modification of Quantum Mechanics have been put forward in the past few decades in order to solve such a dichotomy. Among them, some approaches...

In this paper, our prime objective is to investigate the thermal nature of the de- Sitter space generated due to the entanglement between a pair of Unruh-De-Witt detectors in the paradigm of open quantum systems. The Master-equation of pair of a two-level atomic system within a framework of weakly interacting limit in the de-Sitter space is solved. One of the most important phenomena occurring...

We show that compressible, Riemann-S type ellipsoids can emit gravitational waves (GWs) with a chirp-like structure (chirping ellipsoids, CELs). The potential detection of these type of sources with eLISA and other future space-based GW observatories can reveal previously undetected astrophysical processes in system of compact objects (e.g. the postmerger object of white dwarf binary mergers)....

Kaluza-Klein [1,2] mechanism was rejected for inconsistencies due to the Planck length scale.

Nelson [3] derivation of Quantum Mechanics was rejected for having assumed, without justification, a periodic multivalued action and the presence of universal fluctuations. Both the mechanisms can be reinterpreted without problems at the light of the guiding center (for Kaluza-Klein) and gyrocenter...

I review the approach of *precanonical quantization* based on the structures of the De Donder-Weyl Hamiltonian formulation of field theories. The approach requires no splitting to space and time and it leads to a new understanding of quantum fields as a *hypercomplex* generalization of quantum theory rather than an infinite-dimensional one. A relationship with the standard QFT in the...

We analyze the propagation of gravitational

waves in a medium containing bounded

subsystems ("molecules''), able to induce significant Macroscopic Gravity effects. We establish a precise constitutive relation between the

average quadrupole and the amplitudes of a vacuum gravitational wave, via the geodesic deviation equation. Then we determine

the modified equation for the wave inside the...

The simplicity of black holes, as characterized by no-hair theorems, is one of the most important mathematical results in the framework of general relativity. Are these theorems unique to black hole spacetimes, or do they also constrain the geometry around regions of spacetime with arbitrarily large (although finite) redshift? In this talk I will discuss the answer to this question, showing...

Gravitational-wave standard sirens present a novel approach for the determination of the Hubble constant. After the recent spectacular confirmation of the method thanks to GW170817 and its optical counterpart, additional standard siren measurements from future gravitational-wave sources are expected to constrain the Hubble constant to high accuracy. At the same time, improved constraints are...

The postmerger-ringdown waveform of coalescing, non-precessing, spinning

binary black holes in the \texttt{TEOBresumS} model is given by a closed form, analytic,

time-domain family of template waveforms, informed by a large set of

Numerical Relativity waveforms from different codes such as the BAM code, the SpEC code and

state-of-the-art test-particle waveforms. The NR waveforms cover the...

We improve and generalize to all multipoles the factorization and resummation approach of Nagar and Shah,designed to improve the strong-field behavior of the post-Newtonian (PN) residual waveform amplitudes $f_{\ell m}$'s entering the effective-one-body, circularized, gravitational waveform for spinning coalescing binaries. For a test-particle orbiting a Kerr black hole, each multipolar...

Premetric teleparallel gravity is a generalization of GR based on two field equations similar to Maxwell’s equations of electrodynamics. In gravitational model, the scalar-valued 2-forms of electrodynamics are replaced by two vector-valued 2-forms. The energy-momentum 3-form of matter and gravity field serves as a source. A general linear constitutive relation between two basic fields...

I introduce the concept of fake particle and study how it is used to formulate a consistent theory of quantum gravity. Fakeons arise from a new quantization prescription, alternative to the Feynman one, for the poles of higher-derivative theories, which avoids the problem of ghosts. The fake particles mediate interactions and simulate true particles in many situations. Nevertheless, they are...

We shall present a SO(2) duality-symmetric form of the

linearized ADM action principle when the linearization is performed on

anti de Sitter and Kasner backgrounds. The analysis is based on the

two-potential formalism, obtained upon resolution of the Hamiltonian

constraints, and generalizes previous works that focused on Minkowski

and de Sitter backgrounds. The implications of our results...

It is widely accepted that the general theory of relativity ceases to explain phenomena in the vicinity and inside a black hole. Wheeler holds the idea that on the surface of a Black hole the space parameters turn into quantum foam. He even contemplates on the geometry of space parameters as one zooms down on a point particle. In this work we aim to solve challenges by employing a pair of...

TEOBResumS and SEOBNR are the two mainstream analytical waveform models (informed by numerical-relativity information) that accurately describe the dynamics of two coalescing compact objects of masses m1 and m2 and spins S1 and S2 up to merger and ringdown. Both use the effective-one-body (EOB) approach, which maps the relative dynamics of two objects into the dynamics of a (spinning) particle...

We start from the state-of-the-art effective one-body (EOB) model and suitably expand it up to 5.5PN order in the orbital (nonspinning) case.

By comparing the so-obtained high-order PN phasing with the corresponding EOB one, we conclude that the 5.5PN approximation delivers a reliable phasing description up to $M\omega = 0.05$ for comparable mass binaries. Although such cutoff frequency is...

Although the existence of dark matter (DM) has been shown through various observations, nobody knows the identity of the DM. Axions were firstly introduced to solve the strong CP problem, and one of the possible candidate of DM.

Due to the super-radiance instability, axion cloud is formed around Kerr BHs.

Recently, it was suggested that once coupling to photons is considered, the laser of...

In this work, we study the effect of a magnetic field on the growth of cosmological perturbations. We develop a mathematical consistent treatment in which a perfect fluid and a uniform magnetic field evolve together in a Bianchi I universe. We then study the energy density perturbations on this background with particular emphasis on the effect of the background magnetic field. We develop a...

In this talk we will present a new method to construct homogenous AdS black strings/p-branes in General Relativity and Lovelock gravity. These configurations are obtained by means of a specific "scalar dressing" of the extended coordinates. We will show how to use this method to construct the Schwarzschild AdS black string, the black string extension of the Boulware-Deser black hole and some...

We show that (Eur Phys J C, 2018), the gravity can be considered as defined not by one but two fundamental constants which enables us to explain quantitatively both dark energy (the cosmological constant) in GR equations and dark matter in weak-field limit simultaneously. Then, in order to throw more light on the nature of the constants appearing here, we generalize the Newton theorem on the...

I try to revive, and possibly reconcile, a debate started a few years ago, about the relative roles of a bare cosmological constant and of a vacuum energy, by taking the attitude to try to get the most from the physics now available as established. I take as starting point the proposals on how to regularize the particles vacuum energy without violating Lorentz invariance. I notice that the...

The detection of GW170817, the first neutron star-neutron star merger observed by advanced LIGO and Virgo, and its following analyses represent the first contributions of gravitational wave data to understanding dense matter. Imposing a lower limit on the maximum mass value and parametrizing the high density section of the equation of state of both neutron stars through spectral decomposition...

Basic aspects of the Hamiltonian structure of the parity-violating Poincar\'e gauge theory are studied. We found all possible primary constraints, identified the corresponding critical parameters, and constructed the generic form of the canonical Hamiltonian. In addition to being important in their own right, these results offer dynamical information that is essential for a proper...

Time in physics is always viewed from the point of view of duration, but this interpretation causes many problems and paradoxes. I would like to explore a change of interpretation of time. By thinking time as a cut, many problems could be easily solved. Particularly, with such interpretation, quantum gravity theories based on 3+1 spacetime (e.g. Kuchar or Ellis' evolving block universe) may...

The objective, statistical nature of SDSS astrophysical datasets, which were not driven by any theoretical agenda, reveal false and misleading prior measurements (e.g., redshift-distance) driven by confirmation bias in the context of such agendas. SDSS theta-z, redshift-magnitude (both spectroscopic and photometric pipelines), and galaxy population-density data are shown to conflict with the...

A very general reconstruction and estimation of the gravitational wave features, i.e. not based on prior knowledge of the waveform models, is useful to catch unexpected characteristics of the signal. In addition, it can complement the analyses based on parametrized models of the detected emissions from compact binary coalescences. In fact, we know that parametrized models may not always...

The second observing run of Advanced LIGO and Virgo ended on August 2017 with the detection of several coalescences. We report the results of a general search for gravitational waves of short duration using minimal assumption on the waveforms and sensitive to a wide range of sources. The analysis includes the results of three different algorithms over the frequency from 32 to 4096 Hz targeting...

Gravitational waves (GWs) have been detected from mergers of binary black holes and binary neutron stars.

Core collapse supernovae (CCSNe) are recognized as the most energetic explosions in the modern Universe

The main reason GWs from CCSN have not yet been detected is the low event rate, about one per century,

observable within the Milky Way.

We report on the construction of a Convolutional...

In the context of the unmodelled search for gravitational waves associated to *gamma-ray bursts* (GRB), we present a sensitivity study conducted using *X-Pipeline*, a software which combines the data from LIGO and Virgo in correlation with the GRB direction in the sky. The goal is to understand how the addition of Virgo to the network of interferometers impacts the sensitivity of the search....

We compute the Zero Point Energy (ZPE) induced by quantum fluctuations around a fixed background with the help of a reformulation of the Wheeler-DeWitt equation. A variational approach is used for the calculation with Gaussian Trial Wave Functionals. The one loop contribution of the graviton to the ZPE is extracted keeping under control the UltraViolet divergences by means of a distorted...

Anti-de Sitter spacetime is a solution of Einstein’s equations with a negative cosmological constant. This fact allows for unusual black hole solutions with non-spherical horizon topology. We calculate the renormalised vacuum polarisation for black holes with spherical, flat and hyperbolic event horizons, following the “extended coordinates” method, which uses a mode-sum representation for the...

Driven by the the fact that a wide family of Ricci-based metric-affine theories of gravity can be reduced to a metric compatible framework, a formal correspondence between the space of solutions of these generalized gravity theories and the space of solutions of general relativity will be presented. The correspondence will be detailed in the cases where modified gravity is coupled to scalar...

Using a geocentric ecliptical coordinate system to analyze the data of a proposed new Earth's satellite, provisionally named ELXIS, in a circular orbit perpendicular to both the equator and the reference direction of the Vernal Equinox should allow, in principle, to measure the general relativistic Lense-Thirring and De Sitter effects on the satellite's inclination $I$ and node $\Omega$ to a...

It is well known that a spinning body moving in a fluid suffers a force orthogonal to its velocity and rotation axis --- it is called the Magnus effect. Recent simulations of spinning black holes and (indirect) theoretical arguments suggest that a somewhat analogous effect may occur for purely gravitational phenomena. The magnitude and precise direction of this "gravitational Magnus effect"...

In this talk we will consider the possibility to enlarge the class of symmetries under which a local (polynomial) action is invariant by introducing nonlocal (non-polynomial) operators. In particular, we will show how to construct nonlocal actions, consisting of infinite order derivatives, which are invariant under a wider class of symmetries, containing the Galilean shift symmetry as a...

We consider time-independent scattering of gravitational waves by a compact horizon-less body such as a neutron star. The neutron star is modelled with a polytropic equation of state. The metric perturbation in the exterior can be solved for using the gauge invariant master functions and formalism presented by Martel and Poisson [2005]. For the interior we work in Regge-Wheeler gauge and solve...

Scenarios that strive to describe quantum theory as an emergent, non-primitive concept typically run into difficulties when trying to address a relativistic generalization. In this talk we discuss a possible way out of this situation by showing that the observed relativistic behavior in the quantum world might well be just a statistically emergent phenomenon out of deeper no-relativistic level...

We analyze the semiclassical stability of the Schwarzschild AdS black hole

in the Euclidean partition function approach. We perform this computation

in the large D limit and focus on scalar perturbations. We obtain the equa-

tions for non-spherically symmetric scalar perturbations in a simple form.

For a class of perturbations stability is demonstrated by the S-deformation

method. For some...

In this talk, I explore the Casimir effect for a massless scalar field in the context of a generic curved background. In this perspective, the mean vacuum energy density and the pressure between the binding plates are the relevant physical objects to evaluate. After the above general discussion, a systematic procedure to derive interesting pieces of information on the free parameters of...

In this work, we study the impact of quantum entanglement on the two-point correlation function and the associated primordial power spectrum of mean square vacuum fluctuation in a bipartite quantum field theoretic system. The field theory that we consider is the effective theory of axion field arising from Type IIB string theory compactified to four dimensions. We compute the expression for...

Following Whittaker(*Proc.Roy.Soc.A***116**,720(1927)) we derive the partial differential equation whose solution is the electrostatic potential in curved spaces with the metric given :

a.in 2 + 1 dimensions by i)S.Deser,R.Jackiw and G.'tHooft,*Ann.Phys.152*,220(1984) and G.Clement,Int.J.Theor.Phys.24**,267(1985)and by ii)M.Banados,C.Teitelboim and...

We show that in the post-merger phase of binary neutron star (BNS) merger are present convective instabilities that excite inertial mode oscillations. These oscillations emit gravitational waves in the frequency band where ground-based detectors are within reach of planned third-generation detectors and could be used also as sensitive probes of the rotational and thermal state of matter in the...

We investigate the gravitational radiation from binary systems in conformal gravity (CG) and conformal Einstein-Weyl gravity (CEWG). CG might explain observed galaxy rotation curves without dark matter, and both models are of interest in the context of quantum gravity. Gravitational radiation emitted by compact binaries allows us to strongly constrain both models.

We derive the linearized...

GW170817 with its coincident optical counterpart has led to a first "standard siren" measurement of the Hubble constant independent of the cosmological distance ladder. The Schutz "statistical" method, which is expected to work in the absence of uniquely identified hosts, has also started bringing in its first estimates. In this talk we report the current results of the gravitational-wave...

We derive the form of the partition function in conformal gravity using an extended form of the Faddeev-Popov method. The method uses conformal gauge fixing and special (third) conformal ghosts. In this way, at one-loop, the theory is proven to be conformally invariant also on the quantum level without performing an additional final conformal transformation. The partition function is discussed...

Nowadays, our modeling of the Universe depends critically on our understanding of gravity; despite the fact General Relativity (GR) is the standard theory of gravity, deviations from GR could profoundly impact our conclusions on the best theory suitable to explain the "dark" ingredients that make up the Universe. On the other hand, experimental verifications of the GR weak effects are...

We consider the dynamics of the Mixmaster Universe, focusing on the Bianchi IX cosmological model (this model have a closed Universe with a spherical topology). We use f (R) gravity, which is the simplest modification of the general relativity, considering the Palatini formalism, and compare the results with those of the quadratic correction. To describe the Mixmaster model, we use the Misner...

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. A connection with the Quantum Weak Energy Condition is also presented.

Regular models of black holes replace the central singularity with a

nonsingular spacetime region, in which an effective classical geometric

description is available. It has been argued that these models provide

an effective, but complete, description of the evaporation of black

holes at all times up to their eventual disappearance. However, I will

show that known models fail to be...