Backreaction from non-conformal quantum fields in de Sitter spacetime

TL;DR

This paper investigates how non-conformal quantum fields influence de Sitter spacetime stability, highlighting the importance of non-local effects in maintaining a stable universe in semiclassical gravity.

Contribution

It provides a perturbative analysis of the stress tensor for non-conformal fields in de Sitter space, demonstrating the stabilizing role of non-local terms in the effective action.

Findings

Non-local terms cancel late-time divergences.

De Sitter spacetime remains stable under small perturbations.

Large mass fields exhibit different backreaction behavior.

Abstract

We study the backreaction on the mean field geometry due to a non-conformal quantum field in a Robertson-Walker background. In the regime of small mass and small deviation from conformal coupling, we compute perturbatively the expectation value of the stress tensor of the field for a variety of vacuum states, and use it to obtain explicitly the semiclassical gravity solutions for isotropic perturbations around de Sitter spacetime, which is found to be stable. Our results show clearly the crucial role of the non-local terms that appear in the effective action: they cancel the contribution from local terms proportional to the logarithm of the scale factor which would otherwise become dominant at late times and prevent the existence of a stable self-consistent de Sitter solution. Finally, the opposite regime of a strongly non-conformal field with a large mass is also considered.