Conveners
Parallel Sessions: Session I (SI) - Classical relativity, compact objects, gravitational waves (room 19)
- Andrzej Krolak
Parallel Sessions: Session II (SII) - Quantum gravity, QFT and related topics (room 407)
- Jerzy Lewandowski (University of Warsaw)
Parallel Sessions: Session II (SII) - Quantum gravity, QFT and related topics (room 407)
- Jerzy Lewandowski (University of Warsaw)
Parallel Sessions: Session I (SI) - Classical relativity, compact objects, gravitational waves (room 19)
- Andrzej Krolak
Parallel Sessions: Session III (SIII) – Testing relativity, astrophysics (room 19)
- Marek Rogatko (Maria Curie-Skłodowska University, Lublin, Poland)
Parallel Sessions: Session IV (SIV) – Strings, branes, holography (room 407)
- Piotr Sulkowski
Parallel Sessions: Session V (SV) – Extended gravities (room 407)
- Salvatore Capozziello (INFN - National Institute for Nuclear Physics)
Parallel Sessions: Session VI (SVI) - Cosmology (room 19)
- Adam Balcerzak (University of Szczecin)
Parallel Sessions: Session V (SV) – Extended gravities (room 407)
- Salvatore Capozziello (INFN - National Institute for Nuclear Physics)
Parallel Sessions: Session VI (SVI) - Cosmology (room 19)
- Adam Balcerzak (University of Szczecin)
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.
We consider $3$-dimensional isolated horizons (IHs) generated by null curves that form non-trivial $U(1)$ bundles and the Petrov type D equation. From the $4$-dimensional spacetime point of view, solutions to that equation define isolated horizons embeddable in vacuum spacetimes (with cosmological constant) as Killing horizons to the second order such that the spacetime Weyl tensor at the ...
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...
Perturbation theories play an important role in general relativity and cosmology. Depending on the framework and the quantities we perturb we can distinguish two main approaches in perturbation theories: Eulerian and Lagrangian. Like in the Newtonian theory, relativistic Lagrangian perturbations allow us to get insight into a mildly non-linear stages of structure formation, substantially...
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...
I will discuss recent models of stationary, self-gravitating, magnetized tori (disks) around black holes. They are constructed by solving the coupled set of Einstein equations and the equations of ideal general-relativistic magnetohydrodynamics. In the first part of the talk, I will focus on the impact of the magnetic field on the properties of such tori. If time permits, I will also discuss...
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...
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...
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...
It can be shown that all Robinson-Trautman spacetimes are conformal to Kundt spacetimes. For spacetimes with constant Ricci scalar, all quadratic gravity corrections to Einstein gravity can be combined into the Bach tensor which is well behaved under conformal transformations.
Combining these results leads to a considerable simplification of the vacuum field equation of quadratic gravity...
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,...
We consider a specific type of the bimetric theory of gravitation with the two different metrics introduced in the cosmological frame. Both metrics respect all the symmetries of the standard FLRW solution and contain conformally related spatial parts. One of the metric is assumed to describe the causal structure for the matter. Another metric defines the causal structure for the gravitational...
We consider a generalized Schwarzschild-like ansatz and prove that it can be consistently employed to construct $d$-dimensional static vacuum black hole solutions in any metric theory of gravity for which the Lagrangian is a scalar invariant constructed from the Riemann tensor and its covariant derivatives of arbitrary order. After describing the ansatz and the corresponding (reduced) field...
In my talk I consider self-gravitating toroidal disks around black holes that rotate according to the general-relativistic Keplerian rotation law. During our research on the problem of mass estimation in such systems new effects have been discovered. They concern density and circumferential radius and appear, when disks are massive enough. In my talk I would like to present these effects.
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...
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...
