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Group field theory and its cosmology in a matter reference frame

Gielen, Steffen


Steffen Gielen


While the equations of general relativity take the same form in any coordinate system, choosing a suitable set of coordinates is essential in any practical application. This poses a challenge in background-independent quantum gravity, where coordinates are not a priori available and need to be reconstructed from physical degrees of freedom. We review the general idea of coupling free scalar fields to gravity and using these scalars as a “matter reference frame”. The resulting coordinate system is harmonic, i.e., it satisfies the harmonic (de Donder) gauge. We then show how to introduce such matter reference frames in the group field theory approach to quantum gravity, where spacetime is emergent from a “condensate” of fundamental quantum degrees of freedom of geometry, and how to use matter coordinates to extract physics. We review recent results in homogeneous and inhomogeneous cosmology, and give a new application to the case of spherical symmetry. We find tentative evidence that spherically-symmetric group field theory condensates defined in this setting can reproduce the near-horizon geometry of a Schwarzschild black hole.

Journal Article Type Article
Publication Date Oct 2, 2018
Journal Universe
Print ISSN 2218-1997
Publisher MDPI
Peer Reviewed Peer Reviewed
Volume 4
Issue 10
Pages 103
APA6 Citation Gielen, S. (2018). Group field theory and its cosmology in a matter reference frame. Universe, 4(10), 103.
Keywords quantum gravity; group field theory; harmonic coordinates; spherical symmetry
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