Gravitational Waves and Dark Photon Dark Matter from Axion Rotations

TL;DR

This paper explores how an axion's rotation in field space can generate dark photons and gravitational waves, offering a new cosmological scenario for dark photon dark matter and baryogenesis, with potential observational signatures.

Contribution

It introduces a novel mechanism linking axion rotations to dark photon production, gravitational wave signals, and baryogenesis within a consistent cosmological framework.

Findings

Dark photon background produced via tachyonic instability.

Detectable gravitational wave signals at pulsar timing arrays.

Potential for future 21-cm line surveys to observe warm dark photons.

Abstract

An axion rotating in field space can produce dark photons in the early universe via tachyonic instability. This explosive particle production creates a background of stochastic gravitational waves that may be visible at pulsar timing arrays or other gravitational wave detectors. This scenario provides a novel history for dark photon dark matter. The dark photons may be warm at a level detectable in future 21-cm line surveys. For a consistent cosmology, the radial direction of the complex field containing the axion must be thermalized. We explore a concrete thermalization mechanism in detail and also demonstrate how this setup can be responsible for the generation of the observed baryon asymmetry.