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  Homogeneous cosmologies as group field theory condensates

Gielen, S., Oriti, D., & Sindoni, L. (2014). Homogeneous cosmologies as group field theory condensates. Journal of high energy physics: JHEP, 2014(06): 013. doi:10.1007/JHEP06(2014)013.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-0014-A91A-1 Version Permalink: http://hdl.handle.net/11858/00-001M-0000-001A-2404-4
Genre: Journal Article

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 Creators:
Gielen, Steffen1, Author              
Oriti, Daniele1, Author              
Sindoni, Lorenzo1, Author              
Affiliations:
1Microscopic Quantum Structure & Dynamics of Spacetime, AEI-Golm, MPI for Gravitational Physics, Max Planck Society, ou_67201              

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Free keywords: General Relativity and Quantum Cosmology, gr-qc,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO,High Energy Physics - Theory, hep-th
 Abstract: We give a general procedure, in the group field theory (GFT) formalism for quantum gravity, for constructing states that describe macroscopic, spatially homogeneous universes. These states are close to coherent (condensate) states used in the description of Bose-Einstein condensates. The condition on such states to be (approximate) solutions to the quantum equations of motion of GFT is used to extract an effective dynamics for homogeneous cosmologies directly from the underlying quantum theory. The resulting description in general gives nonlinear and nonlocal equations for the 'condensate wavefunction' which are analogous to the Gross-Pitaevskii equation in Bose-Einstein condensates. We show the general form of the effective equations for current quantum gravity models, as well as some concrete examples. We identify conditions under which the dynamics becomes linear, admitting an interpretation as a quantum-cosmological Wheeler-DeWitt equation, and give its semiclassical (WKB) approximation in the case of a kinetic term that includes a Laplace-Beltrami operator. For isotropic states, this approximation reproduces the classical Friedmann equation in vacuum with positive spatial curvature. We show how the formalism can be consistently extended from Riemannian signature to Lorentzian signature models, and discuss the addition of matter fields, obtaining the correct coupling of a massless scalar in the Friedmann equation from the most natural extension of the GFT action. We also outline the procedure for extending our condensate states to include cosmological perturbations. Our results form the basis of a general programme for extracting effective cosmological dynamics directly from a microscopic non-perturbative theory of quantum gravity.

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 Dates: 2013-11-052014
 Publication Status: Published in print
 Pages: 48 pages (including three appendices), revtex
 Publishing info: -
 Table of Contents: -
 Rev. Method: -
 Identifiers: arXiv: 1311.1238
DOI: 10.1007/JHEP06(2014)013
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Title: Journal of high energy physics : JHEP
Source Genre: Journal
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Publ. Info: Bologna, Italy : Società italiana di fisica
Pages: - Volume / Issue: 2014 (06) Sequence Number: 013 Start / End Page: - Identifier: ISSN: 1126-6708
CoNE: /journals/resource/111021927548002