High Quality QCD Axion at Gravitational Wave Observatories

TL;DR

This paper explores how heavy QCD axion models, which address the strong CP problem without fine-tuning, can be tested through gravitational wave signals and electric dipole moment measurements, with future observatories expanding the search.

Contribution

It demonstrates that generic heavy QCD axion models can be probed by current and future gravitational wave detectors and electric dipole moment experiments.

Findings

LIGO-Virgo-KAGRA can detect GW signals from axionic string-domain wall networks.

Future GW observatories will extend the parameter space coverage for heavy QCD axions.

Electric dipole moment measurements can constrain axion models related to the strong CP problem.

Abstract

The axion solution to the strong CP problem is delicately sensitive to Peccei-Quinn breaking contributions that are misaligned with respect to QCD instantons. Heavy QCD axion models are appealing because they avoid this so-called "quality problem". We show that generic realizations of this framework can be probed by the LIGO-Virgo-KAGRA interferometers, through the stochastic gravitational wave (GW) signal sourced by the long-lived axionic string-domain wall network, and by upcoming measurements of the neutron and proton Electric Dipole Moments. Additionally, we provide predictions for searches at future GW observatories, which will further explore the parameter space of heavy QCD axion models.