Gravitational waves from axion wave production

TL;DR

This paper explores how axion-like particles coupled with Chern-Simons gravity can generate detectable gravitational waves in the early universe through parametric resonance, offering a new production mechanism less constrained than traditional axion-photon interactions.

Contribution

It introduces a novel gravitational wave production channel via axion wave resonance in the early universe, expanding potential detection methods for axion-like particles.

Findings

Gravitational waves can be produced directly from axion wave resonance.

Produced gravitational waves are detectable by current and future detectors.

The mechanism is effective over a broad range of axion parameters.

Abstract

We consider a scenario with axions/axion-like particles Chern-Simons gravity coupling, such that gravitational waves can be produced directly from axion wave parametric resonance in the early universe after inflation. This axion gravity term is less constrained compared to the well-searched axion photon coupling and can provide a direct and efficient production channel for gravitational waves. Such stochastic gravitational waves can be detected by either space/ground-based gravitational wave detectors or pulsar timing arrays for a broad range of axion masses and decay constants.