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Relativity Seminar

usually takes place the first Thursday of each month at 13.30 IM, rear building, ground floor – please check the current calendar
Chair: Marcello Ortaggio. Deputy chair: Vojtěch Pravda
Old web page with some of the seminar history: http://gravity.math.cas.cz/ .

Constructing accelerating NUT black holes

José Barrientos

MÚ AV ČR

Thursday, 15. June 2023 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
LIBRARY

We employ Ehlers transformations, Lie point symmetries of the Einstein field equations, to efficiently endorse accelerating metrics with a nontrivial NUT charge. Under this context, we begin by re-deriving the known C-metric NUT spacetime described by Chng, Mann, and Stelea in a straightforward manner, and in the new form of the solution introduced by Podolský and Vrátný. Next, we construct for the first time an accelerating NUT black hole dressed with a conformally coupled scalar field. These solutions belong to the general class of type I spacetimes, therefore cannot be obtained from any limit of the Plebanśki-Demiański family whatsoever and their integration needs to be carried out independently. Including Maxwell fields is certainly permitted, however, the use of Ehlers transformations is subtle and requires further modifications. Ehlers transformations do not only partially rotate the mass parameter such that its magnetic component appears, but also rotate the corresponding gauge... more

Charged free bosons in 2d and spontaneous symmetry breaking from holography

Felipe Diaz

Universidad Andres Bello

Thursday, 1. June 2023 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
rear building, ground floor

Extending the holographic prescription for obtaining the Renyi entropy in theories with global symmetries to the case where the global symmetries are generated by nonlinear sources, we show that conformal electrodynamics in 2+1 dimensions reproduce the exact same entropies and conformal weight of the generalized twist operators of a two-dimensional conformal complex free boson. Moreover, we consider thermal fluctuations in the gravity partition function which generates new subleading divergences in the entanglement entropy which resembles the one appearing in field theories with spontaneous symmetry breaking due to infrared perturbations of the ground state. We comment on the possibility of interpreting these results in terms of holography beyond the saddle point approximation

Impulsive gravitational waves

Robert Švarc

ÚTF MFF UK

Thursday, 13. April 2023 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
rear building, ground floor

We summarize a suitable construction of exact spacetimes representing expanding gravitational impulses generated by snapped cosmic strings and propagating on the constant curvature backgrounds. The main attention is paid to the geodesic motion analysis, which provides direct insight into the structure of string-like topological defects, their geometric properties, and the resulting physical interpretation of such impulsive solutions.

Radiative nonlinear electrodynamics solutions in Robinson-Trautman geometry

Tayebeh Tahamtan

ÚTF MFF UK

Thursday, 30. March 2023 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
rear building, ground floor

Radiative electromagnetic solutions for several nonlinear electrodynamics models are derived in Robinson-Trautman geometry. Linear perturbations of the obtained solutions are investigated.

Black hole scalarization in Einsteinian Cubic Gravity and its compatibility with cosmic Evolution

Cristián Erices

Universidad Central de Chile

Thursday, 24. November 2022 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
rear building, ground floor

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 context. Interestingly enough, we find that already at this minimal level, there is a nontrivial interplay between the Wilson coefficients which are otherwise completely independent, constraining the parameter space where scalarization may actually occur. Conclusively, we claim that the EFT does exhibit black hole scalarization, remaining compatible with the inflationary paradigm, and admitting general relativity as a cosmological attractor.

Graviton corrections to the Newtonian potential using invariant observables

Markus B. Fröb

Institut für Theoretische Physik, Universität Leipzig

Monday, 26. September 2022 - 13:30 to 14:30

Institute of Mathematics of ASCR, Zitna 25, Praha 1
rear building, ground floor

We consider the effective theory of perturbative quantum gravity coupled to a point particle, quantizing fluctuations of both the gravitational field and the particle's position around flat space. Using a recent relational approach to construct gauge-invariant observables, we compute one-loop graviton corrections to the invariant metric perturbation, whose time-time component gives the Newtonian gravitational potential. The resulting quantum correction consists of two parts: the first stems from graviton loops and agrees with the correction derived by other methods, while the second one is sourced by the quantum fluctuations of the particle's position and energy-momentum, and may be viewed as an analog of a ``Zitterbewegung''. As a check on the computation, we also recover classical corrections which agree with the perturbative expansion of the Schwarzschild metric.

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