Phenomenology of fermion production during axion inflation

TL;DR

This paper analyzes how fermions produced during axion inflation influence primordial perturbations, revealing regimes where fermions dominate the scalar spectrum with minimal non-Gaussianities and can sustain inflation despite steep potentials.

Contribution

It provides analytic insights into fermion effects on scalar perturbations and identifies conditions where fermions dominate or enable inflation without slow-roll.

Findings

Fermions can significantly modify the scalar power spectrum.

A regime exists where fermions dominate the spectrum with small non-Gaussianities.

Fermion backreaction can sustain inflation with steep potentials.

Abstract

We study the production of fermions through a derivative coupling with a pseudoscalar inflaton and the effects of the produced fermions on the scalar primordial perturbations. We present analytic results for the modification of the scalar power spectrum due to the produced fermions, and we estimate the amplitude of the non-Gaussianities in the equilateral regime. Remarkably, we find a regime where the effect of the fermions gives the dominant contribution to the scalar spectrum while the amplitude of the bispectrum is small and in agreement with observation. We also note the existence of a regime in which the backreaction of the fermions on the evolution of the zero-mode of the inflaton can lead to inflation even if the potential of the inflaton is steep and does not satisfy the slow-roll conditions.