Secular effects on inflation from one-loop quantum gravity

TL;DR

This paper investigates how one-loop quantum gravity effects, through non-local logarithmic terms, can cause tiny but secular modifications to the expansion rate of the universe in different cosmological scenarios.

Contribution

It extends previous work by correcting errors and analyzing quantum corrections in both matter-dominated and de Sitter universes, revealing their secular impact on cosmic expansion.

Findings

Quantum corrections can slow down de Sitter expansion.

In matter-dominated universes, corrections tend to accelerate expansion.

Secular effects, though small, accumulate over time.

Abstract

In this paper we revisit and extend a previous analysis where the possible relevance of quantum gravity effects in a cosmological setup was studied. The object of interest are non-local (logarithmic) terms generated in the effective action of gravity due to the exchange in loops of massless modes (such as photons or the gravitons themselves). We correct one mistake existing in the previous work and discuss the issue in a more general setting in different cosmological scenarios. We obtain the one-loop quantum-corrected evolution equations for the cosmological scale factor up to a given order in a derivative expansion in two particular cases: a matter dominated universe with vanishing cosmological constant, and in a de Sitter universe. We show that the quantum corrections, albeit tiny, may have a secular effect that eventually modifies the expansion rate. For a de Sitter universe they tend to slow down the rate of the expansion, while the effect seems to have the opposite sign in a matter dominated universe. To partly understand these effects we provide a complementary newtonian analysis.