Gravitational Wave-Induced Freeze-In of Fermionic Dark Matter

TL;DR

This paper proposes that stochastic gravitational wave backgrounds can induce the gravitational production of fermionic dark matter, potentially explaining its abundance more efficiently than previous mechanisms.

Contribution

It introduces a novel mechanism for fermionic dark matter production via gravitational waves, with detailed 1-loop calculations using in-in formalism.

Findings

Gravitational waves can produce Weyl fermions in the early universe.

The mechanism can account for dark matter abundance if fermions acquire mass.

Production efficiency may surpass that of superheavy fermion models.

Abstract

The minimal coupling of massless fermions to gravity does not allow for their gravitational production solely based on the expansion of the Universe. We argue that this changes in presence of realistic and potentially detectable stochastic gravitational wave backgrounds. We compute the resulting energy density of Weyl fermions at 1-loop using in--in formalism. If the initially massless fermions eventually acquire mass, this mechanism can explain the dark matter abundance in the Universe. Remarkably, it may be more efficient than conventional gravitational production of superheavy fermions.