An axion-like spectator during inflation can trigger a tachyonic instability which amplifies the modes of one of the helicities of the gauge field, resulting in the production of parity-violating gravitational waves (GWs). In this paper we investigate the impact of the coupling RFF of the gauge field to gravity on the production of GWs. We find that such a coupling introduces a multiplicative factor to the tachyonic mass, which effectively enhances the amplitude of the gauge field modes. Produced GWs are expected to be observed by future space-based GW detectors. Additionally, we find that the strong backreaction due to particle production leads to multiple peaks in the energy spectrum of GWs.
@article{arxiv.2409.08312,
title = {Gravitational Waves from a Gauge Field Non-minimally Coupled to Gravity},
author = {Jian-Feng He and Chengjie Fu and Kai-Ge Zhang and Zong-Kuan Guo},
journal= {arXiv preprint arXiv:2409.08312},
year = {2025}
}