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Sebastian Steinhaus (FSU Jena)09/12/2024, 13:55
Spin foam models are a non-perturbative, background independent approach to quantum gravity derived from general relativity formulated as a constrained topological field theory. The sum over histories is codified in group theoretic data associated to a triangulation, which can be understood as area and angle variables. Extracting physics from these models requires efficient numerical...
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Francesco Di Filippo (Charles U)09/12/2024, 14:15
Within the context of general relativity, black holes must contain a singular core. It is widely believed that singularities are not truly a physical feature, but rather a sign indicating the breakdown of the general relativistic description. Among the possible non-singular scenarios, regular black holes and or horizonless ultracompact stars have taken a particular preeminence. In this talk, I...
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Michal Bobula (U Wroclaw)09/12/2024, 14:35
I will discuss a (quantum mechanically) modified model for the Oppenheimer-Snyder collapse scenario where the exterior of the collapsing dust ball is a Hayward black hole spacetime and the interior is a dust Friedmann-Robertson-Walker cosmology. This interior cosmology is entirely determined by the junction conditions with the exterior black hole. It turns out to be non-singular, displaying a...
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Robert Svarc (Charles U)09/12/2024, 16:00
The extension of General Relativity by including quadratic curvature invariants in the Einstein-Hilbert action is one of the most extensively studied alternative gravity theories today. In this contribution, we employ the quadratic gravity field equations, formulated using the Newman-Penrose formalism, to analyse extensions of the Kerr black hole spacetime going beyond GR. We derive...
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Gloria Odak (Charles U)09/12/2024, 16:20
In this work, we compute the Hamiltonian surface charges of gravitational systems under a range of conservative boundary conditions, including Dirichlet, Neumann, and York’s mixed boundary conditions, where the conformal induced metric and the trace of the extrinsic curvature are fixed. We demonstrate that for all these boundary conditions, the canonical approach produces results consistent...
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Marek Liška (Dublin IAS)09/12/2024, 16:40
The covariant phase space construction first introduced by J. Lee and R. Wald represents a versatile computational tool. It allows us to compute Noetheresque conserved quantitites in a number of different settings, and also to straightforwardly compare various theories of gravity. In my talk, I show how to extend this formalism beyond the class of diffeomorphism invariant theories, in...
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David Kubiznak (Charles U)10/12/2024, 13:55
Kerr-NUT-AdS spacetimes possess hidden symmetries encoded in the so-called principal Killing-Yano tensor. Focusing on 4 dimensions, we present a number of symmetry operators for scalar, vector, and tensor perturbations, that are of degree 2 (to be defined) and homogeneous in the principal tensor.
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Milton Ruiz (U Valencia)10/12/2024, 14:15
The oscillation modes of neutron star (NS) merger remnants, as encoded by the kHz post-merger gravitational wave (GW) signal, hold great potential for constraining the as-yet undetermined equation of state (EOS) of dense nuclear matter. Previous works have used numerical relativity simulations to derive quasi-universal relations for the key oscillation frequencies, but most of them omit the...
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Kabir Chakravarti (Czech Academy of Sciences)10/12/2024, 14:35
Binary compact object mergers are the result of typically tens to hundreds of million years of evolution. Such evolution follows specific pathways, the details of which at current state-of-art are not yet completely understood. These gaps in our understanding are expected to leave residual ambiguities in the prediction of the astrophysical merger rate which can potentially turns out to bias...
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Petra Suková (Czech Academy of Sciences)10/12/2024, 16:00
In recent years, a mysterious new class of astrophysical objects has been uncovered. These objects are spatially coincident with the nuclei of external galaxies and exhibit X-ray variations that repeat over timescales ranging from minutes to months. They manifest in three distinct ways in the data: stable quasi-periodic oscillations (QPOs), quasi-periodic eruptions (QPEs), and quasi-periodic...
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Shilpa Sarkar (Harish Chandra Research I)10/12/2024, 16:20
We investigate accretion flows around rotating black holes (BHs) and obtain self-consistent transonic solutions in full general relativistic prescription. The flow is assumed to be viscous and radiative. Viscosity helps in the removal of angular momentum outwards, allowing matter to get accreted inwards. In addition, viscous heat dissipated makes the matter hotter. On the other hand, radiation...
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Zexin Hu (Tübingen U)10/12/2024, 16:40
Future observations with next-generation radio telescopes are expected to discover radio pulsars closely orbiting around Sagittarius A (Sgr A), the supermassive black hole (SMBH) at our Galactic Center (GC). Such a system can provide a unique laboratory for measuring the spacetime of SMBH and testing gravity theories. We provide a numerical timing model for the pulsar-SMBH systems based on the...
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Georgios Loukes-Gerakopoulos (Czech Academy of Sciences)11/12/2024, 13:55
Teukolsky equation allows the study of perturbations of the Kerr metric in linear approximation. We shall discuss how the solution of this equation can be used to compute the evolution of an extreme mass ratio inspiral, where a stellar compact object inspirals towards a supermassive black hole due to gravitational radiation reaction. We will address both time domain and frequency domain...
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Angelica Albertini (Charles U)11/12/2024, 14:15
The effective-one-body (EOB) approach is a powerful formalism that maps the two-body problem in general relativity into the motion of a single body in an effective metric. EOB-based waveform models are nowadays providing fast and accurate templates for comparable-mass coalescing compact binaries, where the latter are the events observed by the currently operating detectors. Third-generation...
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Davide Usseglio (SSM Napoli)11/12/2024, 14:35
Self Force Analytical computations has been used in the past years as an useful tool to calibrate the numerical simulations of waveforms for EMRIs. At the same time, in the field of Scattering Amplitudes, a lot of parallel work has been done in trying to compute observables related to the unbound two-bodies scattering. It has also emerged a theoretical argument that shows how it is possible to...
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Ondřej Zelenka (Czech Academy of Sciences)11/12/2024, 16:00
Conventional searches for gravitational wave signals in detector data are computationally demanding and struggle when certain transient noise sources are present. Recently, machine-learning algorithms have been proposed to address current and future challenges. We present a neural-network based algorithm to search for binary black hole waveforms. We also apply our algorithm to real O3b data...
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David Kofron (Charles U)11/12/2024, 16:20
The study of black hole perturbations typically follows two main approaches: the direct metric perturbation and perturbation via the Newman-Penrose (NP) or Geroch-Held-Penrose (GHP) formalism. In the latter case, a reconstruction method is required, such as the Debye (or Hertz) potential method, to obtain the corresponding metric perturbation. However, the reconstructed metric is expressed in...
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Petr Kotlařík (Czech Academy of Sciences)11/12/2024, 16:40
When a black hole rings due to some external perturbation it emits gravitational waves described by quasi normal modes (QNMs) – a series of exponentially damped harmonic oscillations. If the final state is fully described by the Kerr(-Newman) metric, this ring-down carries a unique signature of its parameters encoded in the modes' complex frequencies. However, astrophysical black holes are...
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