Title: Gravity with null boundaries
Language: English
Authors: Freisinger, Dominik 
Qualification level: Diploma
Advisor: Grumiller, Daniel 
Issue Date: 2019
Number of Pages: 55
Qualification level: Diploma
Abstract: 
We study null boundary segments intersecting each other at non-smooth corners. As a result, a null analog to the common Gibbons-Hawking-York (GHY) counterterm [1,2] and corner counterterms, containing Lorentz angles between hypersurface normals, are presented. Considering that, we follow loosely the treatments in [35] and obtain a slightly more general result. As a prototype spacetime that exhibits null and timelike boundary segments connected via non-smooth corners, we investigate a Bañados-Teitelboim-Zanelli (BTZ) black hole (BH) [6, 7]. The BTZ solution does not preserve Dirichlet boundary conditions (bcs) and therefore needs holographic counterterms added to the action such that we get a well-defined action principle (I| EOM = 0). We show that on the asymptotic (timelike) boundary segment r it is not possible to construct a suitable counterterm solely out of covariant quantities and therefore propose a non-covariant counterterm that can be interpreted as a dilaton-like scalar field on the boundary. Furthermore we show that we cannot find any counterterms to the corner contributions in the action integral such that the variation vanishes. We propose to fix the boost gauge in a suitable manner such that corners do not contribute at all. The full action is then given by the standard Einstein-Hilbert (EH) action plus GHY-like counterterms on the null segments and a non-covariant term on the asymptotic boundary. For the ease of the calculations we work in 2 + 1 dimensions.
Keywords: gravity; null boundaries
URI: https://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-128973
http://hdl.handle.net/20.500.12708/4456
Library ID: AC15475116
Organisation: E136 - Institut für Theoretische Physik 
Publication Type: Thesis
Hochschulschrift
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