Gravitational Waves from Supercool Axions

TL;DR

This paper explores how different Peccei-Quinn phase transition dynamics in axion models can produce detectable gravitational waves, with potential signals observable by current and future interferometers.

Contribution

It identifies conditions under which the PQ phase transition is strongly first order, leading to significant supercooling and gravitational wave production, a novel insight into axion cosmology.

Findings

First order phase transitions produce strong gravitational wave signals.

Predicted gravitational wave frequencies are within LIGO's sensitivity.

Future detectors can thoroughly test these axion models.

Abstract

We study the dynamics of the Peccei-Quinn (PQ) phase transition for the QCD axion. In weakly coupled models the transition is typically second order except in the region of parameters where the PQ symmetry is broken through the Coleman-Weinberg mechanism. In strongly coupled realizations the transition is often first order. We show examples where the phase transition leads to strong supercooling lowering the nucleation temperature and enhancing the stochastic gravitational wave signals. The models predict a frequency peak in the range 100-1000 Hz with an amplitude that is already within the sensitivity of LIGO and can be thoroughly tested with future gravitational wave interferometers.