Production of dark matter axions from collapse of string-wall systems

TL;DR

This paper investigates the spectrum of axions emitted during the collapse of domain walls in axion models through lattice simulations, revealing their low relativistic nature and impact on dark matter abundance constraints.

Contribution

It provides a comprehensive simulation of the entire defect evolution process, including string formation, domain wall creation, and their annihilation, focusing on axion spectra and dark matter implications.

Findings

Axions from domain wall collapse have a low-frequency peak.

Decay of defects can significantly contribute to dark matter axion abundance.

Results impose stricter bounds on the axion decay constant.

Abstract

We analyze the spectrum of axions radiated from collapse of domain walls, which have received less attention in the literature. The evolution of topological defects related to the axion models is investigated by performing field-theoretic lattice simulations. We simulate the whole process of evolution of the defects, including the formation of global strings, the formation of domain walls and the annihilation of the defects due to the tension of walls. The spectrum of radiated axions has a peak at the low frequency, which implies that axions produced by the collapse of domain walls are not highly relativistic. We revisit the relic abundance of cold dark matter axions and find that the contribution from the decay of defects can be comparable with the contribution from strings. This result leads to a more severe upper bound on the axion decay constant.