The era of gravitational-wave (GW) astronomy is now well under way, with nearly 100 compact binary coalescences (CBCs) confidently detected in the first three observing runs of LIGO and Virgo. With the fourth observing run of LIGO, Virgo and KAGRA starting in early 2023, it is timely to review what has been learned so far, both from the CBC events and from the absence of other types of GW...
We have entered the era of gravitational wave (GW) astronomy with routine detections of GW signals by LIGO-Virgo-KAGRA interferometric detectors. Future perspectives are bright with new generations of GW detectors: Earth based - Einstein Telescope and Cosmic Explorer or space borne - LISA, DECIGO, BBO. Gravitaional waves traveling along null geodesics can undergo strong gravitational lensing...
We analyze about a thousand globular cluster (GC) models simulated using the MOCCA Monte Carlo code for star cluster evolution to study black hole - black hole interactions in these dense stellar sys- tems that can lead to gravitational wave emission. We extracted information for all coalescing binary black holes (BBHs) that merge via gravitational ra- diation from these GC models and for...
We offer a mathematical toolkit for the study of waves propagating on a background manifold with nonvanishing torsion. As an example, we briefly analyze the amplitude propagation of gravitational waves in an Einstein-Cartan-Sciamma-Kibble (ECSK) assuming a dark matter spin tensor sourcing for spacetime torsion at cosmological scales and assess whether a future detection by LISA is possible.
Problem of finding effective banks of templates is very important in match filtering method used in detection of almost monochromatic gravitational waves coming from single rotating neutron stars located in our Galaxy. Construction of effective banks of templates requires finding optimal grid coverings in the space spanned by unknown parameters of the gravitational-wave signal we are looking...
In the context of the late time cosmic acceleration phenomenon, many geometrically modified theories of gravity have been proposed in recent times. In this paper, we have investigated the role of a recently proposed extension of symmetric teleparallel gravity dubbed as $f(Q,T)$ gravity in getting viable cosmological models, where $Q$ and $T$ respectively denote the non-metricity and the trace...
The standard model of cosmology currently allows for three types of geometries (or topologies) for our Universe (Euclidean, spherical or hyperbolic), each of these types corresponding to a set of different (multiconnected)-topologies. Among these geometries, Newton’s theory of gravity is only defined on the Euclidean one. Still, extending the validity of this theory to the other two cases...
The talk will deliver insight into the general relativistic conservative binary dynamics through the fifth post-Newonian (5PN) order. Through the 4PN order, the well established methods and results get summarized. At the 5PN order, a recently completed computation is presented including comparisons with the literature. Partial results through the 6PN order get reported.
I will talk about images of black holes in Saggittarius A* and M87 obtained with the Event Horizon Telescope. Both images have a ring-like morphologies consisstent with predictions of magnetohydrodynamical simulations of gas dynamics in Kerr metric. EHT results provide new window for future tests of gravitational physics and unique way to observe physics of accretion and jet formation around...
The code HARM_COOL, a conservative scheme for relativistic magnetohydrodynamics, is being developed in our group and works with a tabulated equation of state of dense matter. This EOS can be chosen and used during dynamical simulation, instead of the simple ideal gas one. In this case, the inversion scheme between the conserved and primitive variables is not a trivial task. In principle, the...
Neutrino-cooled accretion flow around a spinning black hole, produced by a compact binary merger is a promising scenario for jet formation and launching magnetically and neutrino-driven outflows. Based on GW170817 gravitational wave detection by LIGO and Virgo observatories followed by electromagnetic counterparts, this model can explain the central engine of the short duration gamma ray...
Pushed by a number of advances, electromagnetic observatories have now reached the horizon scale of supermassive black holes. The existence and properties of horizons in our universe is one of the outstanding fundamental issues that can now be addressed. Here we investigate the ability to discriminate between black holes and compact, horizonless objects, focusing on the lensing of hot spots...
Current multi-messenger approach has made it possible to get a much more precise estimation of stellar observables like mass $M$ and radius $R$ of a neutron star which consequently can help us constrain the neutron star equation of state (EOS) like never before. Theoretical stellar models are being refined accordingly. Using Chandrasekhar's variational method, we examine the dynamical...
I will discuss the relation between the angular diameter distance and parallax distance in general relativity. This relation involves the curvature tensor along the line of sight and the difference between distance measures can be used to measure the matter content along the line of sight. Moreover, it is also possible to prove that the parallax distance must be not smaller than the angular...
We study the structure and temporal variabilty properties of the GRB jets considering a magnetically arrested disk as their central engine. We numerically evolve the accretion disk around a Kerr black hole using 3D general relativistic magnetohydrodynamic simulations. We consider two analytical equillibrium disk configurations, the Fishbone-Moncrief and Chakrabarti solutions, as the initial...
Numerical simulations have been an important method for studying complex astrophysical scenarios, such as supernova explosions, showing that the remnant of core-collapse supernova rotates differentially at the initial phase of evolution. For neutron stars, differential rotation allows for significantly larger masses than rigid rotation. In our work, we study the stability of those objects and...
The coadjoint representation of the BMS group is worked out from purely group theoretic considerations. It is then identified in the non-radiative gravitational data at null infinity.
We show that conformal geodesics on a Riemannian manifold cannot spiral: there does not exist a conformal geodesic which becomes trapped in every neighbourhood of a point. This settles an outstanding open problem in General Relativity posed by Friedrich. This is joint work with Peter Cameron and Paul Tod.
In this short talk I will discuss the explicitly-solvable toy-model for the problem of waves propagating outside of an extremal black hole. After showing some results regarding quasinormal modes in such setup I will move to the more complicated case of an extremal Reissner-Nordström-anti-de Sitter black hole. This is a joint work with Claude Warnick.
The talk is devoted to the neutral 4-dimensional spaces. As a basic structure we consider weak, expanding hyperheavenly space, i.e., a space equipped with (at least one) integrable, totally null, 2-dimensional distribution which is not parallely propagated. It is assumed that this distribution is self-dual (SD). If a space is additionally equipped with two anti-self-dual (ASD), parallely...
The theory of Schwarzschild timelike geodesics is revisited. Based on Weierstrass and Biermann's result, a formula describing all non radial, timelike trajectories in terms of Weierstrass elliptic functions is derived. A single formula works for an entire geodesic trajectory, even if it passes through turning points. Additionally, with this formula's help, expressions for the proper and...
I will present recent results on evolving black holes in general relativity. Approximate analytical solutions are obtained by expanding the Einstein field equations close to the trapping horizon for a dynamical spherically symmetric black hole in the presence of a minimally coupled self-interacting scalar field. This is made possible by a new parametrization of the metric, in which the...
Using an efficient pattern-based computational method of generating the so-called ‘resonating’ algebraic structures results in a wide class of the new Lie (super)algebras. They are enlargements of the Poincaré and Anti-de-Sitter (super)algebras, which inherit their base (anti)commutation structure. Obtained superalgebras are rooted in the semigroup expansion method and Maxwell and...
It is not only known that hairy black holes can exist in asymptotically Anti-de Sitter (AdS) spaces, but also that in the context of the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence, such black holes can be interpreted as holographic duals of superfluids. After a perturbation, these black holes usually exhibit an exponentially damped ringing down described by quasi-normal...
We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. At infinity the gas obeys the Maxwell-Juttner distribution, restricted to the equatorial plane. In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular...
We study the simplest possible analytical model for spherical collapse that involves density variations, that of a homogeneous core surrounded by a different homogeneous layer, where both are joined using the Darmois matching conditions. The aim is to obtain an analytical expression for whether or not a naked singularity forms, in terms of both mass densities. Although there have been several...
Linearized gravity could be treated as a linear theory of a field having symmetries of the Weyl tensor (spin-2 field). To obtain linearized gravity equations in this formulation from a variational formula, it is necessary to have a guarantee of the existence of potential for every spin-2 field. This problem is known as an existence of Lanczos potential, which has been fully solved by F. Bampi...
The Halilsoy solution corresponds to cross-polarized standing gravitational waves in cylindrical symmetry. In my talk, I will present recent results on the structure of this spacetime and particles' orbits.
We address the issue of black hole scalarization and its compatibility with cosmic inflation and big bang cosmology from an effective field theory (EFT) point of view. In practice, using a well-defined and healthy toy model which (in part) has been broadly considered in the literature, we consider how higher-order theories of gravity, up to cubic operators in Riemann curvature, fit within this...
Quasinormal modes (QNMs) are the exponentially damped, oscillatory solutions to linearized wave equations that appear in a variety of physical contexts. Most notably, the gravitational waves emitted during the ringdown phase of the merger of two compact objects, such as neutron stars or black holes, are characterized by QNMs. The frequencies of the QNMs encode information about the relic...
Hopfions are a family of `solitonary’ field solutions which have non-trivial topological structure associated with Hopf fibration. I will present a generalisation of such solutions, based on conformal transformations, to de Sitter spacetime. Two physical applications of Hopfion-like solutions: electromagnetism and linear gravitation will be discussed.
The talk concerns the current status of matter fields in the framework of loop quantum gravity, with an emphasis on the recent developments. The presentation will particularly focus on the r-Fock representations and their relation to the standard loop representations, in light of the recent generalization of the construction of r-Fock measures to SU(N) gauge theories, and how one could try...
In the model of a fermion field coupled to loop quantum gravity, we consider the Gauss and the Hamiltonian constraints. According to the explicit solutions to the Gauss constraint, the fermion spins and the gravitational spin networks intertwine with each other so that the fermion spins contribute to the volume of the spin network vertices. For the Hamiltonian constraint, the regularization...
We introduce a new operator representing the three-dimensional scalar curvature in loop quantum gravity. The classical starting point of our construction is to express the Ricci scalar directly as a function of the Ashtekar variables. The construction does not apply to the entire Hilbert space of loop quantum gravity; instead, the operator is defined on the Hilbert space of a fixed cubical...
I will discuss the extensions of Heisenberg Uncertainty Principle onto the gravitational interaction both in small (generalized) and large (extended) scales. Then I will review our results related to the GUP in various nonextensive thermodynamics of black hole and cosmological horizons.
t is well known that gravity in 2+1 dimensions can be recast as the Chern-Simons theory, with the gauge group given by the local isometry group, depending on the metric signature and the cosmological constant. Point particles are added into spacetime as (spinning) conical defects. Then, in principle, one may integrate out the gravitational degrees of freedom to obtain the effective particle...
In this work we explore the quantum Bianchi type IX-model, its semi-classical features, and its relevance in early cosmology to tentatively explain inflation and production of primordial structures. We specially focus on the analytical and numerical exploration of the dynamical system derived from the phase-space portraits. Afterwards we investigate the reliability of our results with regard...
We quantize the solution to the Belinski-Khalatnikov-Lifshitz scenario using the affine coherent states quantization method. Quantization smears the gravitational singularity avoiding its localization in the configuration space. Classical chaotic behavior of the BKL scenario becomes enhanced at the quantum level. Our results strongly suggest that the generic singularity of general relativity...
Quantization of classical models is a non-unique and heuristic procedure. A set of different, in fact non-equivalent approaches is known. In the talk some principles of the integral quantization method is presented. The simplest integral quantization procedure is based on decomposition of unity in the Hilbert state space. More sophisticated way of thinking in this direction is related to the...
The appearance of Hamiltonian constraint in the canonical formalism for general relativity reflects the lack of any preferred notion of time. The dynamics of general relativistic systems can be equivalently expressed with respect to various internal degrees of freedom. However, quantization of general relativistic systems breaks down the diffeomorphism invariance and different time variables...
One of the possible applications of quantum computers in the near future are simulations of physics. An example are quantum gravitational systems associated with the Planck scale physics. Such systems are expected to be of the many-body type, which justifies utility of quantum computations in the analysis of their complex quantum behaviour. In this talk, simulation of loop quantum gravity on...
The galaxy bispectrum will play an important role for future galaxy surveys. On large scales it will be a key probe for measuring primordial non-Gaussianity, and hence help discriminate between different inflationary models and other theories of the early universe. On these scales, a variety of relativistic effects come into play once the galaxy number-count fluctuation is projected onto the...
In my talk, I will argue that the GUT scale is the most natural scale for inflation. I will show why we may actually need to go much lower and why this may cause massive fine-tuning. Finally, I will present a possible solution - warm inflation with (almost) arbitrarily low energy scale.
We present a special case of the plane symmetric model from the G_3/S_2-symmetric space-times solving the Einstein equations for a dust source which exhibits a controlled form of the growth of the matter density inhomogeneities.
In this talk I will present the specific solution to the second-order cosmological perturbation theory. For the background I will consider any Friedmann-Lemaitre-Robertson-Walker model filled with a dust, and a positive cosmological constant. The presented model is a generalization of the previous results obtained with Krzysztof Głód where the background was the Einstein-de Sitter spacetime....
We investigate the possibility of gravitationally generated particle production via the mechanism of non-minimal curvature-matter coupling. An intriguing feature of this theory is that the divergence of the matter energy-momentum tensor does not vanish identically. We explore the physical and cosmological implications of the non-conservation of the energy-momentum tensor by using the formalism...
Extended gravity theories modify gravitational phenomena at various scales, ranging from cosmological to the scale of our Solar System. Given the multitude of possible modifications, it is essential to test the models at different energy regimes. Gravity is well-tested here on Earth; any deviations from general relativity (GR) should be miniscule, which imposes some limitations on possible...
We investigate the FLRW cosmological model with a non-minimally coupled scalar field generalized according to the methods given by the nonlinear field space theory. In this approach, one generalizes the phase space of a given field to a topological space (such as symplectic manifold). We consider the compactification of the phase space to a spherical case, corresponding to a spin system, and...
Scalar tensor theories (STT) of gravity are one of the most fundamental types of modified theories of gravity. By introducing a non-minimally coupled dynamical scalar field, they make it possible to describe gravitational interaction to the extent that the purely tensor general theory of relativity fails, or does not give sufficiently accurate predictions. One of the ideas strongly developed...
In this work, we have investigated some rip cosmological models in an extended symmetric teleparallel gravity theory. We consider the form f (Q, T ) = aQ^m+bT in the Einstein–Hilbert action and expressed the field equations and the dynamical parameters in terms of the non-metricity Q. Three rip models such as Little Rip, Big Rip, and Pseudo Rip are presented also the energy conditions and the...
In the context of the late time cosmic acceleration phenomenon, many geometrically modified theories of gravity have been proposed in recent times. In this paper, we have investigated the role of a recently proposed extension of symmetric teleparallel gravity dubbed as $f(Q,T)$ gravity in getting viable cosmological models, where $Q$ and $T$ respectively denote the non-metricity and the trace...
The talk addresses the possibility of obtaining cosmologically relevant effects from the quantum nature of the Hubble horizon. We show that the Planck scale discreteness of the Hubble horizon naturally leads to a mechanism of condensation in the very early Universe. We argue that this provides a possible resolution of the problem of the initial homogeneity at the onset of inflation....
