Inhomogeneous universe from group field theory condensate

Gielen, Steffen

Abstract

One of the fundamental challenges for quantum cosmology is to explain the emergence of our macroscopic Universe from physics at the Planck scale. In the group field theory (GFT) approach to quantum gravity, such a macroscopic universe results from the formation of a "condensate" of fundamentally discrete degrees of freedom. It has been shown that the effective dynamics of such GFT condensates follows the classical Friedmann dynamics at late times, while avoiding the classical singularity by a bounce akin to the one of loop quantum cosmology (LQC). It was also shown how quantum fluctuations in a GFT condensate provide an initial power spectrum of volume fluctuations around exact homogeneity. Here we connect the results for quantum fluctuations in GFT to the usual formalism for cosmological perturbations within quantum field theory in curved spacetime. We consider a bouncing universe filled with a massless scalar field, in which perturbations are generated by vacuum fluctuations in the contracting phase. Matching conditions at the bounce are provided by working within LQC. We then compare the results to the GFT condensate scenario for quantum gravity with massless scalar matter. Here, instead, an initial quantum phase described by a GFT condensate generates initial scalar perturbations through quantum fluctuations. We show general agreement in the predictions of both approaches, suggesting that GFT condensates can provide a physical mechanism for the emergence of a slightly inhomogeneous universe from full quantum gravity.

Citation

Gielen, S. (2019). Inhomogeneous universe from group field theory condensate. Journal of Cosmology and Astroparticle Physics, 2019(2), https://doi.org/10.1088/1475-7516/2019/02/013

• Journal Article Type: Article
• Acceptance Date: Jan 31, 2019
• Online Publication Date: Feb 11, 2019
• Publication Date: Feb 11, 2019
• Deposit Date: Feb 14, 2019
• Publicly Available Date: Feb 14, 2019
• Journal: Journal of Cosmology and Astroparticle Physics
• Electronic ISSN: 1475-7516
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 2019
• Issue: 2
• Article Number: 13
• DOI: https://doi.org/10.1088/1475-7516/2019/02/013
• Keywords: Bouncing cosmology; Group field theory; Cosmological perturbation theory
• Public URL: https://nottingham-repository.worktribe.com/output/1547179
• Publisher URL: https://iopscience.iop.org/article/10.1088/1475-7516/2019/02/013/meta
• Additional Information: This is an author-created, un-copyedited version of an article accepted for publication in Journal of Cosmology and Astroparticle Physics. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.1088/1475-7516/2019/02/013