Late-time backreaction from inflationary fluctuations of a non-minimally coupled massless scalar

TL;DR

This paper investigates the late-time quantum backreaction effects of inflationary fluctuations of a non-minimally coupled massless scalar field, revealing significant impacts depending on the coupling parameter and inflation duration.

Contribution

It provides a detailed analysis of the late-time backreaction from inflationary fluctuations of a non-minimally coupled scalar, highlighting conditions for significant effects and sign changes.

Findings

Large backreaction for negative nonminimal coupling 

Backreaction becomes significant for  ew  in coupling

Backreaction sign changes near minimal inflation duration

Abstract

We consider the late time one-loop quantum backreaction from inflationary fluctuations of a non-minimally coupled, massless scalar field. The scalar is assumed to be a spectator field in an inflationary model with a constant principal slow roll $\epsilon$ parameter. We regulate the infrared by matching onto a pre-inflationary radiation era. We find a large late time backreaction when the nonminimal coupling $\xi$ is negative (in which case the scalar exhibits a negative mass term during inflation). The one-loop quantum backreaction becomes significant today for moderately small non-minimal couplings, $\xi\sim -1/20$, and it changes sign (from negative to positive) at a recent epoch when inflation lasts not much longer than what is minimally required, $N \gtrsim 66$. Since currently we do not have a way of treating the classical fluid and the quantum backreaction in a self-consistent manner, we cannot say decidely whether the backreaction from inflationary quantum fluctuations of a non-minimally coupled scalar can mimic dark energy.