On August 17th, 2017, merger of binary neutron stars was observed

for the first time by gravitational-wave and electromagnetic telescopes.

Optical and infrared observations in particular agree broadly with

the prediction by numerical relativity. From this April, advanced

LIGO and VIRGO will start observation again and we expect

a few more observations of neutron-star mergers (including...

Here we will discuss two questions related to black-hole mimickers: a) whether echoes from a compact object, if observed, should necessarily mean a qualitatively non-Einsteinian behavior near its surface or may also indicate presence of astrophysical environment? b) whether a perfect, stable black-hole mimicker is possible in the form of a Schwarzschild star.

I will discuss existence, properties, and an effective description of standing gravitational waves in general relativity.

One of the most popular points of view on Linearized Gravity is a Massless Spin-2 Particle Theory. This theory often serves as a starting point to formulate a quantum version of gravity theory. The Spin-2 Field has a well defined local energy density equal to $\frac12(E^2 + B^2)$ in analogy to Maxwell Electrodynamics. However, obtaining this energy formula from Hamiltonian formulation is not...

We study the instability of a Reissner-Nordström-AdS (RNAdS) black hole under perturbations of a massive scalar field coupled to Einstein tensor. Calculating the potential of the scalar perturbations we find that as the strength of the coupling of the scalar to Einstein tensor is increasing, the potential develops a

negative well outside the black hole horizon, indicating an instability of...

The effective field theory (EFT) turns out to be an instrument of an immense value in all aspects of modern particle physics being theory, phenomenology or experiment. In this talk I will show how to extend the systematic top down approach to construction of the EFT proposed by Hitoshi Murayama (LBL, Berkeley) and separately by John Ellis (King’s Coll. London) groups to the curved spacetime....

I will present some preliminary results on the evolution of perturbations in quantum cosmological spacetimes. The classical framework is derived with the Dirac procedure from the second order ADM formalism. Then the framework is quantised covariantly, i.e., respecting the symmetries of the phase space. Next, a semi-classical framework is established and the evolution of perturbations in...

Conformal Yano-Killing (CYK) tensor is a generalization of Killing vector to anti-symmetric two-form which describes so called hidden symmetries. (3+1) decomposition of CYK tensor enables one to construct charges from initial data in a new, simple and geometric way. I will present the construction and compare it with traditional ADM approach. Joint work with Jacek Jezierski.

We discuss the relation between the canonical Hamilton-Jacobi theory and the

De Donder-Weyl Hamilton-Jacobi theory known in the calculus of variations using the

examples of a scalar field on curved space-time background and general relativity.

We show that the canonical Hamilton-Jacobi equation of general relativity which preceded

the Wheeler-De Witt formulation of quantum gravity...

Two-sided conformally recurrent complex and real 4-dimensional spaces are considered. It is proved, that such spaces are equipped with nonexpanding congruence of totally null and geodesic 2-dimensional surfaces, null strings. Two-sided conformally recurrent heavenly spaces of the Petrov-Penrose type [D] are considered. Also, some real slices of type [D] heavenly metric are discussed.

During last POTOR's conference I discussed a quantum gravity model defined by Causal Dynamical Triangulations (CDT) where spatial slices of equal proper time have fixed topology of a 3-torus. Identification of phase structure and order of the phase transitions constitute first steps in the quest for a continuum limit of CDT where, following the asymptotic safety conjecture, the resulting...

Causal Dynamical Triangulations is a nonperturbative approach to quantum gravity based on Regge calculus, which uses lattice regularization in the form of a triangulation. To describe the theory for dimension higher than 2 only numerical simulations are available. It is well known through the numerical simulations, that for certain values of bare coupling constants the de-Sitter Universe...

We present a largely non-technical review of loop quantum gravity, describing its basic principles and recent results in applications to cosmology and black holes.

I will present the recent development of numerical tools for GR MHD modeling of the black hole accretion flows.

The black hole appears as the result of a binary neutron star merger, and is surrounded by a remnant debris torus.

The code named HARM_COOL is our implementation of the existing algorithm

for a conservative GR MHD scheme.

The newly added modules cover the neutino cooling and the...

I will briefly show how low mass stars (<0.08 of the solar mass) allow to test modified theories of gravity. Palatini stars will be the main example.

In my talk I will present a simple idea of Supergravity with flat Kahler geometry. I will show how it may lead to simple scalar potentials, which in principle may lead to inflation or dark energy. Furthermore, I will show how a simple generalization of a simplest flat Kahler leads to generic inflationary potentials from the simplest, linear Superpotentials.

It is widely argued, especially in the phenomenological approach to quantum gravity, that at the Planckian scales the geometry of spacetime may become noncommutative. A closely related effect is the generalization of classical spacetime symmetries into quantum-deformed algebras and groups, which are expected to have the structure of Hopf algebras and be characterized by the (classical)...

It is made a post-Newtonian analysis of a class of Palatini $f(R)$ theories of gravity where the lagrangian density is assumed to be a polynomial function of the Ricci scalar. The resulting metric is not covered by the classical parametrized post-Newtonian formalism (PPN) since new gravitational potentials emerges. I will then discuss post-Newtonian equations of motion of massive bodies and...

Gamma ray bursts are highly energetic and brightest explosions that have been observed in EM spectrum. These can last from few seconds to few hours. The progenitors of long GRBs are believed to be massive stars exploding due to the collapse of their cores. Matter from the star around the core falls down towards the center forming a gaseous envelope and (for rapidly rotating stars) swirls into...

Interactions among black holes and branes could have been relevant in the early stages of the evolution of the Universe. Primordial black holes could have formed out of matter density perturbations, while phase transitions in the cooling Universe may have resulted in an occurrence of extended topological defects. There can exist two types of static configurations within the brane - black hole...

We have modelled the accretion disk around the primary black hole in the binary black hole system OJ 287 as a self-gravitating, stationary torus of barotropic matter in Keplerian motion. Using a consistently general-relativistic approach, we found solutions that satisfy either geometric requirements on the disk or the requirements on its mass density

found by Lehto, Valtonen, and their...

Cosmography can be considered as a sort of a

model-independent approach to tackle the dark energy/modified gravity

problem. In this talk, the success and the shortcomings of the

$\Lambda$CDM model, based on General Relativity and standard model of

particles, are discussed in view of the most recent observational

constraints. The motivations for considering extensions and modifications

of...

Gravitational waves offer a unique window to study the strong-field regime of general relativity. In 1916-18, Einstein showed their existence in linearized approximation which was followed by a period of confusion. Finally cemented theoretically by Bondi, Sachs, Trautman gravitational waves are an important tool to discover new information about fundamental gravity effects.

One of the...

We present a cosmological model where the cosmological constant is a topological invariant. The cosmological constant is derived from the curvature of exotic $R^4$ embedded in $K3\# \overline{\mathbb{C}P^2}$. Both of the manifolds are perfectly smooth however the 3-diemnsional slices they generate contain topological changes. Then the value of cosmological constant is expressed via...

The presence of a gravitational field modifies significantly particle decay rates compared to the usual Minkowski space results. Because of the lack of energy conservation, new particle processes, forbidden in Minkowski space, are to be considered leading to new Feynman diagrams even at first order. I will give a brief introduction to the problems one encounters when trying to calculate decay...

Space-time curvature affects quantum uncertainty. This effect is commonly known as the Extended Uncertainty principle. In this talk I briefly present a method to calculate the influence of curvature on the uncertainty relation. Moreover I apply it to cosmological and Rindler horizons and interpret the results in the context of horizon thermodynamics.

In my talk I will present a method to quantise and solve the dynamics of gravitational waves in a quantum Friedmann-Lemaitre-Robertson-Walker spacetime filled with radiation.

The classical model is formulated in the ADM formalism. The system is then de-parametrised and reduced phase space is found. With the use of phase space symmetry respecting quantisation map the perturbed quantum FLRW...

After a (necessarily) short introduction about why and how General Relativity, assumed as the established consensus gravity theory, should be modified/extended, we will discuss the constraints we obtained for a particular class of Extended Theory of Gravity (technically defined as “Beyond Horndeski” and “Vainshtein-breaking” theory), using data from clusters of galaxies, both from X-ray...

The Kerr metric, which describes the geometry surrounding an isolated, rotating compact object, is unique in general relativity (GR), in the sense that all asymptotically flat, stationary, vacuum black holes must be locally isometric to the Kerr spacetime. As such, probing the Kerr metric is one of the best means to test GR. However, because modified theories of gravity are often built such...

The kinematical phase space of classical gravitational field is flat (affine) and unbounded. Because of this, field variables may tend to infinity leading to appearance of singularities, which plague Einstein's theory of gravity. During the talk the idea of generalizing the theory of gravity by compactification of the phase space will be discussed. The procedure of compactification of the...

Analytical models which generalize the Friedmann-Lemaitre-Robertson-Walker space-time are important tools in the analysis of a possible impact of the large-scale structure inhomogeneities on the cosmological observables (angular diameter distance-redshift relation, local measurements of the Hubble constant, etc.)

In this talk I will present some progress in the construction of the dust-like...

The Taub-NUT metric represents quite intriguing space-time configuration supposedly possessing gravitational analog of the magnetic monopole. We will deal with the new approach to this subject. Starting from realizing that the source of many inconsistencies lies in neglecting the effects of the wire singularities present in that solution, we are able to explain the existence of the NUT...

The theory of $f(T)$ gravity shall be discussed in the context of gravitoelectromagnetism (GEM) where the modified GEM equations are discussed and derived. Through use of linearisation and perturbation techniques, specific metric solutions are obtained which are then used to investigate specific GEM effects such as the de Sitter and Lense-Thirring precessions. Following observations from...

We present a covariant approach to the problem of light beam propagation in cosmological models. We develop our considerations within the framework of classical geometric optics in general relativity. Using the concept of screen surface orthogonal to the observer velocity and to the bundle of geodesics, we introduce covariant four-dimensional definitions for Sachs and Jacobi fields and for the...

At first we define Riemannian geometry in general relativity (GR) as geometry determined by Riemannian, Finsler-like metric

\begin{equation}

h_{ab}(x;v) :=2V_a V_b - g_{ab}(x).

\end{equation}

Here $g_{ab}$ is the Lorentzian metric of a spacetime and ${\vec v}$ is an unit timelike vector field: $v = \sqrt{g_{ab}v^a v^b} =1$. Then, we compare this Riemannian geometry with original,...

On September 14th, 2015 the LIGO-Virgo collaboration made the first direct detection of gravitational waves, nearly one hundred years after Einstein first predicted them. Since, several gravitational waves have been detected, and we have been able to study new black holes and analyse the collision of two neutron stars. Now the Advanced LIGO and Advanced Virgo observatories are on their third...

Canonical quantization of massive symmetric rank-two tensor in string theory has been studied.

The Lagrangian describing symmetric rank-two tensor, containing two Stueckelberg fields,

was obtained by Siegel and Zwiebach from string field theory. Performing canonical analysis,

we found that the Lagrangian possesses first class constraints only, which generate a local gauge transformation....

I outline the approach of precanonical quantization applied to a scalar field on curved space-time. It leads to the description of quantum fields as sections of the Clifford bundle over the bundle of field variables over space-time. The approach does not require 3+1 decomposition and the corresponding description of quantum fields is a hypercomplex rather than an infinite-dimensional...

Antisymmetric tensor fields arise naturally in superstring theory as well as in some theories with broken Lorentz invariance. However, models containing antisymmetric tensor fields often include anisotropic pressure. I will present a general prescription for constructing ansäzte for antisymmetric tensor fields for use in cosmology. With a series of coordinate-dependent constraints I will show...

The Einstein's theory of gravity, General Relativity was build on the theory of Special Relativity. This generalisation required utilising the full generality of the Riemannian geometry. Many of the present-day cosmological tests of GR are still based on the assumption of the Riemannian geometry. However, in order to fully study and test various extensions of GR one is also required to move...

If one analyses the quantum creation of the universe, it turns out that the most natural way in which the universes can be created is in pairs of universes whose time flow is reversely related. It means that the matter that propagates in one of the universes can be seen, from the point of view of the other universe, as antimatter, and viceversa. They thus form a universe-antiuniverse pair....

It is widely believed that in the presence of positive cosmological constant, heavy black holes can exhibit behaviour different than the standard Hawking radiation, namely there is a possibility of anti-evaporation of such objects. We point out that all those results (obtained in different frameworks) rely heavily upon the identification of the Naiari spacetime with the Schwarzschild--de...

In 2013, Koushik Balasubramanian presented a 5+1 dimensional holographic toy model that allows for an exact solution to Einstein's equations in the bulk in which the isometries of 𝐴𝑑𝑆5 appear to be broken to an isometry group describing a discretely scale invariant and Poincare invariant setup [arXiv:1301.6653]. By analytically solving the Killing equations, we prove that the full 𝐴𝑑𝑆5...

Gravitational waves offer a unique window to study the strong-field regime of general relativity. In 1916-18, Einstein showed their existence in linearized approximation which was followed by a period of confusion. Finally cemented theoretically by Bondi, Sachs, Trautman gravitational waves are an important tool to discover new information about fundamental gravity effects.

One of the...

In light of the promising and imminent multi-messenger observational era, we suggest a method to constrain the cosmological background by future observation involving gravitational lensing of radiation emitted by a gravitational wave source.

We measure the impact of different cosmological parameters in the value of the time delay due to gravitational lensing. The measured time delay is...

Rigid rotation has gained a lot of interest in the field of relativistic heavy ion collisions due to the experimentally observed polarization of the Lambda hyperons [1]. This polarization can be explained via various mechanisms (spin-orbit coupling [2], axial chemical potential [3]) using quantum field theory at finite temperature. On Minkowski space, exact expressions can be obtained for...

Despite the fact that the exact de Sitter space is free of spacetime singularity, the absence of singularity in inflationary universe is still non-trivial. I will focus on singularity problem of two kinds of inflationary universe: past asymptotic de Sitter space and torus compactified de Sitter space. In the former case, I find that the presence of the singularity depends on how fast the scale...