Gielen, S. orcid.org/0000-0002-8653-5430 and Mickel, L. orcid.org/0000-0002-6749-8494 (2022) Gauge-Invariant perturbations at a quantum gravity bounce. Universe, 9 (1). 29. ISSN 2218-1997
Abstract
We study the dynamics of gauge-invariant scalar perturbations in cosmological scenarios with a modified Friedmann equation, such as quantum gravity bouncing cosmologies. We work within a separate universe approximation which captures wavelengths larger than the cosmological horizon; this approximation has been successfully applied to loop quantum cosmology and group field theory. We consider two variables commonly used to characterise scalar perturbations: the curvature perturbation on uniform-density hypersurfaces ζ and the comoving curvature perturbation R. For standard cosmological models in general relativity as well as in loop quantum cosmology, these quantities are conserved and equal on super-horizon scales for adiabatic perturbations. Here we show that while these statements can be extended to a more general form of modified Friedmann equations similar to that of loop quantum cosmology, in other cases, such as the simplest group field theory bounce scenario, ζ is conserved across the bounce whereas R is not. We relate our results to approaches based on a second-order equation for a single perturbation variable, such as the Mukhanov–Sasaki equation.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. |
Keywords: | quantum gravity; cosmological perturbation theory; bouncing universe; group field theory; loop quantum cosmology |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > School of Mathematics and Statistics (Sheffield) |
Funding Information: | Funder Grant number ROYAL SOCIETY UF160662 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 30 Jan 2023 14:16 |
Last Modified: | 30 Jan 2023 14:16 |
Published Version: | http://dx.doi.org/10.3390/universe9010029 |
Status: | Published |
Publisher: | MDPI AG |
Refereed: | Yes |
Identification Number: | 10.3390/universe9010029 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:195779 |