Back Reaction Of Perturbations In Two Scalar Field Inflationary Models

TL;DR

This paper investigates how long-wavelength perturbations influence the local expansion rate during two-field inflation, showing that back-reaction effects can be significant and potentially observable in certain models.

Contribution

It provides a detailed analysis of infrared back-reaction effects in two-field inflationary models, highlighting their potential observability and impact on cosmic expansion.

Findings

Infrared back-reaction terms do not vanish at fixed clock field values.

Back-reaction of entropy modes can become significant in specific models.

Back-reaction effects may be locally observable in general.

Abstract

We calculate the back-reaction of long wavelength cosmological perturbations on a general relativistic measure of the local expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by two scalar matter fields, one being the inflaton and the other one representing a matter field which is used as a clock. We analyze back-reaction in a phase of inflaton-driven slow-roll inflation, and find that the leading infrared back-reaction terms contributing to the evolution of the expansion rate do not vanish when measured at a fixed value of the clock field. We also analyze the back-reaction of entropy modes in a specific cosmological model with negative square mass for the entropy field and find that back-reaction can become significant. Our work provides evidence that, in general, the back-reaction of infrared fluctuations could be locally observable.