Relativity Seminar
of the Institute of Theoretical Physics

Seminar is held on Tuesdays at 13:10 pm in the lecture room of the Institute
on the 10th floor of the department building at Trója, V Holešovičkách 2, Prague 8

May 18, 2021
Zoom link:
Shell shall not stop me! Unruh-DeWitt detection of spacetime features
Ms. Wan Cong
Perimeter Institute for Theoretical Physics, Waterloo, Ontario

The Unruh-DeWitt (UDW) detector was introduced originally to give an operational meaning to particle detection in curved spacetimes. This simple two level quantum system interacts with the quantum field through a monopole type coupling, possibly exciting it to the excited state in the process. As the vacuum state of the field depends on global features of the background spacetime, the transition probability of a detector may be able to pick up these features too. As a result, UDW can be better-than-classical-detectors. Specifically, we shall see that UDW detectors are able to detect the presence and rotation of a massive spherical shell enclosing them even though the spacetime inside the shell is Minkowskian. Moreover in the case of a cylindrical shell, both the interior and exterior spacetimes are locally flat, but there is a conical deficit present outside the shell. This can also be detected by detectors placed in the shell.

May 25, 2021
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Quantum imprints of gravitational shockwaves
Dr. David Kubizňák
Perimeter Institute for Theoretical Physics, Waterloo, Ontario

Gravitational shockwaves are simple exact solutions of Einstein equations representing the fields of ultrarelativistic sources and idealized gravitational waves (shocks). Historically studied abundantly in the context of possible black hole formation in high energy particle collisions, they are at the forefront of research even today. Representing hard modes in the bulk, shocks give rise to the gravitational memory effect at the classical level and implant supertranslation (BMS) hair onto a classical spacetime at the quantum level. The aim of this paper is to further our understanding of the ‘information content’ of such supertranslations. Namely, we show that (contrary to the several claims in the literature) a gravitational shockwave does leave a quantum imprint on the vacuum state of a test quantum field and that this imprint is accessible to local observers carrying Unruh-DeWitt (UDW) detectors in this spacetime.

June 1, 2021
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Accelerating Taub-NUT black hole
Mr. Adam Vrátný

An exact solution of Einstein's equations will be described which represents an accelerating black hole with a NUT parameter. The solution was found by Chng, Mann and Stelea in 2006. A new convenient form of this metric will be presented, together with its algebraic, geometric and physical properties.

Jiří Bičák                                                                                                  Oldřich Semerák