Peccei-Quinn Phase Transition at LIGO

TL;DR

This paper explores the potential for LIGO to detect gravitational waves from early universe phase transitions related to Peccei-Quinn symmetry breaking, highlighting conditions for strong signals and implications for future detectors.

Contribution

It analyzes conditions for strong first-order Peccei-Quinn phase transitions and their gravitational wave signatures, including scenarios with electroweak symmetry breaking at high scales.

Findings

Detectable gravitational wave signals require some supercooling.

Strong first-order transitions can occur in Coleman-Weinberg or strongly-coupled models.

Signals from high-scale electroweak breaking may be observed by Einstein Telescope.

Abstract

The LIGO observatories can potentially detect stochastic gravitational waves arising from phase transitions which happened in the early universe at temperatures around $T\sim 10^{8}$ GeV. This provides an extraordinary opportunity for discovering the phase transition associated with the breaking of the Peccei-Quinn symmetry, required in QCD axion models. Here we consider the simplest Peccei-Quinn models and study under which conditions a strong first-order phase transition can occur, analyzing its associated gravitational wave signal. To be detectable at LIGO, we show that some supercooling is needed, which can arise either in Coleman-Weinberg-type symmetry breaking or in strongly-coupled models. We also investigate phase transitions that interestingly proceed by first breaking the electroweak symmetry at large scales before tunneling to the Peccei-Quinn breaking vacuum. In this case, the associated gravitational wave signal is more likely to be probed at the proposed Einstein Telescope.