Graviton backreaction on the local cosmological expansion in slow-roll inflation

TL;DR

This paper calculates the one-loop quantum graviton correction to the local expansion rate during slow-roll inflation, revealing a finite secular effect that can either accelerate or decelerate cosmic expansion based on slow-roll parameters.

Contribution

It introduces a gauge-invariant method to compute graviton backreaction in slow-roll inflation with finite parameters, extending previous de Sitter and constant deceleration results.

Findings

Quantum correction produces a finite secular effect.

Effect can accelerate or decelerate expansion depending on slow-roll parameters.

Results generalize previous findings in specific inflationary models.

Abstract

We compute the graviton one-loop correction to the expectation value of the local expansion rate in slow-roll inflation, with both slow-roll parameters finite. The calculation is based on a recent method to explicitly construct gauge-invariant observables in perturbative quantum gravity at all orders in perturbation theory, and it is particularly suited in cases of highly-symmetrical space-time backgrounds. Our analysis adds to recent calculations of that correction in de Sitter space-time and in single-field inflation with constant deceleration. In the former case a vanishing one-loop correction was found, while in the latter the quantum backreaction produces a secular effect that accelerates the expansion. The quantum correction we describe here produces a finite secular effect that can either accelerated or decelerate the background expansion, depending on the value of the slow-roll parameters.