QCD Axion Dark Matter with a Small Decay Constant

TL;DR

This paper proposes a new cosmological mechanism for QCD axion dark matter production via parametric resonance, allowing for smaller decay constants and potential deviations from cold dark matter in large-scale structures.

Contribution

It introduces a novel origin for axion dark matter through parametric resonance, expanding viable decay constant ranges below previous thresholds.

Findings

Axion decay constants can be as low as 10^8 GeV.

The mechanism can produce warm dark matter effects.

Potential observable deviations in large-scale structure.

Abstract

The QCD axion is a good dark matter candidate. The observed dark matter abundance can arise from misalignment or defect mechanisms, which generically require an axion decay constant $f_a \sim \mathcal{O}(10^{11})$ GeV (or higher). We introduce a new cosmological origin for axion dark matter, parametric resonance from oscillations of the Peccei-Quinn symmetry breaking field, that requires $f_a \sim (10^8 -10^{11})$ GeV. The axions may be warm enough to give deviations from cold dark matter in Large Scale Structure.