Relativistický seminář
Ústavu teoretické fyziky

Seminář se koná v úterý ve 13:10 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8

6. prosince 2022
The Dynamics of Apparent Horizons in a Black Hole Collision (Zoom talk)
Robie A. Hennigar
Department of Quantum Physics and Astrophysics, Institute of Cosmic Sciences, University of Barcelona
(seminář v angličtině)
Apparent horizons are commonly used in numerical relativity to characterize the boundary of a black hole. While a theoretical understanding of the event horizon’s dynamics during a merger has been known for about half a century, significant progress on the corresponding problem for the apparent horizon has been occurring only very recently. In this talk, I will discuss the dynamical evolution of the apparent horizon as it is now understood. Time permitting, I will discuss how various behaviours for marginally outer trapped surfaces observed during the merger can be recovered by studying much simpler, isolated eternal black holes.

Zoom link
13. prosince 2022
The geometry of spacetime from quantum measurements
Tales Rick Perche
Perimeter Institute for Theoretical Physics / University of Waterloo
(seminář v angličtině)

General relativity describes spacetime as a 4 dimensional Lorentzian manifold. The spacetime metric allows one to compute space and time separations between events in spacetime. However, general relativity is a classical theory, and it is not expected to be valid in scales where quantum effects become relevant, such as for distances of the order of the Planck length. In regimes where quantum field theory is valid, one can instead define spacetime separations through correlation functions of a quantum field. In fact, it has been conjectured before that the geometry of spacetime might be emergent from entanglement present in quantum fields. In this description the metric becomes effective, and can be seen as a consequence of the presence of a quantum field in the background spacetime. Moreover, these correlations can be accessed, so that one can rebuild the geometry of spacetime simply by performing quantum measurements on a quantum field.

20. prosince 2022
Simulating particle acceleration in astrophysical shocks
Dr. Allard Jan van Marle
ELI Beamlines, Institute of Physics of the Czech Academy of Sciences
(seminář v angličtině)

Cosmic-rays are charged particles that have been accelerated to relativistic speeds. The general consensus is that the acceleration occurs in astrophysical shocks, with the particles gaining momentum as they repeatedly cross the shock front. In order to understand this process and determine which types of shock contribute to which part of the cosmic-ray spectrum, we need to run numerical simulations that incorporate both the large-scale shock structure and the microphysics of the interaction between charged particles and the local magnetic field. Here we introduce a combined particle-in-cell (PIC) and magnetohydrodynamics (MHD) code that combines the best aspects of both aspects into a single model. This allows us to run large-scale models of astrophysical shocks, incorporating both the particle acceleration process and the feedback of this process on the shock. From these models we can estimate how the characteristics of individual shocks influence their ability to accelerate particles and contribute to the cosmic-ray spectrum.

Jiří Bičák                                                                                                  Oldřich Semerák