**Bianca Dittrich, Perimeter Institute**

**Title: A holographic description for boundary gravitons in 4D**

PDF of the talk (5M)

Audio+Slides< of the talk (38M)

By Jorge Pullin, LSU

Holography has become a central concept in gravity. It is the idea that the description of gravity in a region of spacetime can be mapped to the description of a quantum field theory on the boundary of the spacetime. It originated in string theory as part of the "Maldacena conjecture" but it proved to be a more fundamental concept that does not require string theory for its formulation.

In this talk, holography was first reviewed in the context of three dimensional spacetimes, where the theory of gravity is much simpler than in four space-time dimensions, as spacetimes are locally flat in 3D. In particular, the example of the torus was discussed in detail. It was presented how to use Regge calculus (an approximation to general relativity using a triangulation in terms of simplices) to construct the boundary theory.

The talk then moved to four dimensional spacetimes starting with the simpler example of the flat sector of gravity where one only considers flat spacetimes. Again, the boundary theory was constructed using Regge calculus and the example of the three torus was discussed. It concluded with some future directions for the full theory, discussion of the symmetry group of the theory at infinity and possible implications for black hole entropy.

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