Gravitational waves from axion-like particle cosmic string-wall networks

TL;DR

This paper explores how gravitational waves generated by axion-like particle cosmic string-wall networks could be detected by future cosmological observations, providing insights into dark matter composition and early universe phenomena.

Contribution

It introduces a novel mechanism linking ALP string-wall annihilation to detectable gravitational waves across a wide mass range.

Findings

Gravitational waves from ALP networks could be observed if produced below 100 eV.

Detection is possible for ALPs with masses from 10^{-16} to 10^{6} eV.

ALPs could account for all dark matter if these gravitational waves are observed.

Abstract

Axion-like particles (ALPs) are a compelling candidate for dark matter (DM), whose production is associated with the formation of a string-wall network. If walls bounded by strings persist, which requires the potential to have multiple local minima ($N>1$), they must annihilate before they become dominant. They annihilate mostly into gravitational waves and non-relativistic ALPs. We show that for ALPs other than the QCD axion these gravitational waves, if produced at temperatures below 100 eV, could be detected by future cosmological probes for ALPs with mass from $10^{-16}$ to $10^{6}$ eV that could constitute the entirety of the DM.