# Gravitational waves from fermion production during axion inflation

## TL;DR

This paper analytically investigates gravitational waves generated during axion inflation due to fermion production, finding that the signal is suppressed and does not surpass standard vacuum fluctuation mechanisms, remaining within observational bounds.

## Contribution

It provides the first analytic calculation of the gravitational wave spectrum from fermion production during axion inflation, highlighting suppression of polarization and compatibility with current bounds.

## Key findings

- Polarized gravitational wave component is parametrically suppressed.
- Gravitational wave amplitude cannot exceed standard vacuum fluctuation signals.
- Produced gravitational waves are consistent with current observational constraints.

## Abstract

We present analytic results for the gravitational wave power spectrum induced in models where the inflaton is coupled to a fermionic pseudocurrent. We show that although such a coupling creates helically polarized fermions, the polarized component of the resulting gravitational waves is parametrically suppressed with respect to the non-polarized one. We also show that the amplitude of the gravitational wave signal associated to this production cannot exceed that generated by the standard mechanism of amplification of vacuum fluctuations. We previously found that this model allows for a regime in which the backreaction of the produced fermions allows for slow-roll inflation even for a steep inflaton potential, and still leads to Gaussian primordial scalar perturbations. The present analysis shows that this regime also results in a gravitational wave signal compatible with the current bounds.