Coarse-Grained Back Reaction in Single Scalar Field Driven Inflation

TL;DR

This paper develops a stochastic coarse-graining method to analyze the back reaction of long wavelength perturbations in single-scalar inflation, revealing conditions under which back reaction can be significant and potentially lead to primordial black holes.

Contribution

It introduces a self-consistent stochastic approach including metric and scalar fluctuations, exploring back reaction effects up to second order in inflation models.

Findings

Back reaction is negligible during the last 70 e-foldings for smooth potentials.

Non-smooth potentials can produce significant back reaction.

Such potentials may generate primordial black holes, offering observational constraints.

Abstract

We introduce a self-consistent stochastic coarse-graining method, which includes both metric and scalar field fluctuations, to investigate the back reaction of long wavelength perturbations in single-scalar driven inflation, up to the second (one loop) order. We demonstrate that, although back reaction cannot be significant during the last 70 e-foldings of inflation with a smooth potential, there exist non-smooth inflaton potentials which allow significant back reaction, and are also consistent with cosmological observations. Such non-smooth potentials may lead to the generation of massive primordial black holes, which could be further used to constrain/verify these models.