Relativistický seminář

Seminář se koná v úterý ve 13:10 (není-li řečeno jinak) v posluchárně ÚTF MFF UK v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8

Příští semináře:

3. listopadu 2026: Theory meets implementation in the small mass-ratio limit: From self-force perturbation theory to high-fidelity gravitational waveforms; Dr. Zach Nasipak; University of Southampton; (seminář v angličtině); Space-based gravitational wave detectors such as LISA will observe stellar-mass compact objects spiralling into massive black holes over months to years. These extreme-mass-ratio inspirals (EMRIs) will provide exquisite tests of general relativity and probe the environments of galactic nuclei. That science depends on modelling their dynamics and gravitational signals accurately over hundreds of thousands of orbits. Gravitational self-force theory meets this challenge by treating the smaller body as a perturbation of the larger black hole's spacetime and expanding Einstein's equations in powers of the small mass ratio. Combined with a multiscale separation of the slow inspiral from the fast orbital motion, this approach yields models that are both accurate and efficient. However, implementing the theory in practical high-fidelity tools for gravitational wave data analysis is far from straightforward. In this talk, I will present FastEMRIWaveforms (FEW), a framework that combines self-force theory with GPU-accelerated computation to generate years-long waveforms in milliseconds. I will discuss how advances in self-force theory have shaped FEW and how practical modelling demands are, in turn, driving new theoretical developments. Finally, I will show how these advances allow FEW to accurately describe inspirals with mass ratios as large as 1:8. This opens a promising path toward modelling a much broader range of binaries with the speed and accuracy of the self-force framework.
10. listopadu 2026: Black hole thermodynamics beyond leading order in higher-curvature gravity; Dr. Cristóbal Laporte; University of Barcelona; (seminář v angličtině); Higher-curvature terms in effective theories of gravity modify the thermodynamics of black holes. The Reall–Santos method offers a shortcut: the leading correction to the free energy follows from the uncorrected solution alone, with no need to solve the modified field equations. In this talk, I apply this approach to a range of higher-derivative extensions of the Einstein–Hilbert action, focusing on quasi-topological gravities up to quintic order in arbitrary dimensions and on generalized quasi-topological gravities. Since these theories admit exact or well-controlled static black hole solutions, they offer a clean testing ground for the perturbative method at high orders. I also discuss what changes when the action includes covariant derivatives of the curvature, and outline how the method can be extended to Kerr-type ansatz, where exact solutions are no longer available and a perturbative treatment becomes essential.
17. listopadu 2026: no seminar; (seminář v angličtině)
24. listopadu 2026: TBA; Cynthia Arias Pruna; ITP, Charles University; (seminář v angličtině)

Minulé semináře:

27. října 2026: Separation of spinning-particle motion in Kerr-NUT-(A)dS spacetimes; Dr. Viktor Skoupý; ITP, Charles University; (seminář v angličtině); The motion of spinning bodies in curved spacetimes is affected by the coupling between their spin and the curvature of the background, which makes it more complicated than the motion of nonrotating test bodies. However, if there are enough independent constants of motion, the motion is integrable, and often there exists a set of coordinates in which the Hamilton–Jacobi equation separates. It has recently been shown that if the background spacetime admits separation of both the geodesic equations and parallel transport, then the motion of spinning bodies is separable as well. In this talk, I will show that parallel transport, and thus the Hamilton–Jacobi equation for spinning bodies, is separable in Kerr-NUT-(A)dS spacetimes of any dimension. The proof relies on the construction of a parallel-transported frame and closely parallels known separability results in these spacetimes, such as the separability of geodesic motion and of the massive vector field equations, both of which are made possible by the presence of hidden symmetries.
20. října 2026: no seminar - rest well after Mala Skala :); N/A; (seminář v angličtině)
18. října 2026: Beyond the Kerr paradigm: the dynamical fate of black-hole interiors; Prof. Stefano Liberati; SISSA; (seminář v angličtině); Black holes are usually pictured as long-lived Kerr geometries formed by gravitational collapse, changed only gradually by slow, nearly adiabatic Hawking evaporation. But is this picture right? Classical black-hole interiors contain spacetime singularities, which quantum gravity is expected to resolve, and Cauchy horizons, which are generically unstable under classical and semiclassical perturbations. The usual assumption is that the resulting new physics stays hidden behind the event horizon until late in the evaporation. I will argue that this assumption should be reconsidered. Starting from the hypotheses of the singularity theorems, I will outline a geometric classification of regular black holes and their horizonless counterparts. I will then ask whether their interiors can form and persist in realistic semiclassical collapse. Recent semiclassical numerical results point to cascades of trapped and anti-trapped regions. I will show that complementary analytical models capture this behaviour qualitatively. On this view, black holes may be transient phases of a regular, evolving spacetime, and their interiors may actively shape their fate. I will discuss the evidence for this and the self-consistent backreaction calculations needed to establish it.
13. října 2026: Physical Black Holes: Properties and Observational Tests; Prof. Daniel Terno; Macquarie University in Sydney; (seminář v angličtině); A physical black hole is a light-trapping region whose apparent horizon forms in finite time for a distant observer, irrespective of whether an event horizon exists. Recent work shows that, if such objects form, their near-horizon geometry is not merely a dynamical version of the Schwarzschild or Kerr picture: it has unusual structural properties and features that differ substantially from eternal black holes. The central question is whether these differences can become observationally relevant. We take first steps toward this problem by developing effective near-horizon and interpolating descriptions suitable for computing signatures such as light rings and quasinormal modes. In addition, cosmological embedding provides a sharp test: hypothetical physical black holes do not couple to the large-scale structure of the Universe. Together, these results begin to translate the finite-time formation requirement into observational signatures and broader tests of the standard black-hole paradigm.
6. října 2026: Classical-quantum gravity as quantum gravity in disguise; Dr. Sebastian Murk; Charles University; (seminář v angličtině); Whether gravity must be quantized remains one of the biggest open problems in fundamental physics. Classical-quantum hybrid theories have recently attracted attention as a possible framework in which gravity is treated classically yet interacts consistently with quantum matter. In particular, schemes based on completely positive dynamics preserve a consistent probabilistic description while enabling a systematic treatment of quantum backreaction. In this talk, I will show that completely positive classical-quantum dynamics admits an embedding into a fully quantum theory on an enlarged Hilbert space that faithfully reproduces the hybrid evolution. Consequently, experimental agreement with the predictions of this framework would not by itself establish that gravity is fundamentally classical. In the quantum realization, the hybrid degrees of freedom form an open subsystem, for which symmetries of the dynamics need not imply the corresponding conservation laws. As an illustrative example, I will consider a fully closed hybrid system consisting of a qubit interacting with a classical particle and show that its completely positive dynamics violates total angular momentum conservation despite rotational symmetry of the equations of motion.

David Kubizňák <david.kubiznak@matfyz.cuni.cz>; Oldřich Semerák <oldrich.semerak@matfyz.cuni.cz>

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