Stochastic Background of Gravitational Waves from Fermions

TL;DR

This paper develops a formalism to calculate the gravitational wave spectrum generated by fermions produced during early Universe phenomena like preheating, revealing potential signals for future detectors in certain scenarios.

Contribution

It introduces a new method to compute gravitational wave spectra from fermions and explores their detectability in early Universe models.

Findings

Fermion production can generate a significant stochastic gravitational wave background.

Typical frequencies are outside current detection ranges, but small-coupling scenarios may be observable.

The formalism addresses regularization issues in the calculation.

Abstract

Preheating and other particle production phenomena in the early Universe can give rise to high- energy out-of-equilibrium fermions with an anisotropic stress. We develop a formalism to calculate the spectrum of gravitational waves due to fermions, and apply it to a variety of scenarios after inflation. We pay particular attention to regularization issues. We show that fermion production sources a stochastic background of gravitational waves with a significant amplitude, but we find that typical frequencies of this new background are not within the presently accessible direct detec- tion range. However, small-coupling scenarios might still produce a signal observable by planned detectors, and thus open a new window into the physics of the very early Universe.