Axion dark matter from topological defects

TL;DR

This paper refines estimates of axion dark matter abundance produced by topological defects in the universe, identifying specific axion mass ranges consistent with observed cold dark matter, and discusses uncertainties in numerical simulations.

Contribution

It provides updated, more accurate calculations of axion production from topological defects using improved field-theoretic simulations, exploring different domain wall models.

Findings

Axions with mass $0.8-1.3 imes 10^{-4}$ eV can account for dark matter in certain models.

Higher axion masses up to $10^{-2}$ eV are possible with mild parameter tuning.

Numerical uncertainties and their impact on axion abundance estimates are discussed.

Abstract

The cosmological scenario where the Peccei-Quinn symmetry is broken after inflation is investigated. In this scenario, topological defects such as strings and domain walls produce a large number of axions, which contribute to the cold dark matter of the universe. The previous estimations of the cold dark matter abundance are updated and refined based on the field-theoretic simulations with improved grid sizes. The possible uncertainties originated in the numerical calculations are also discussed. It is found that axions can be responsible for the cold dark matter in the mass range $m_a=(0.8-1.3)\times 10^{-4}\mathrm{eV}$ for the models with the domain wall number $N_{\rm DW}=1$, and $m_a\approx\mathcal{O}(10^{-4}-10^{-2})\mathrm{eV}$ with a mild tuning of parameters for the models with $N_{\rm DW}>1$. Such higher mass ranges can be probed in future experimental studies.