Parametric-Resonance Production of QCD Axions

TL;DR

This paper shows that primordial temperature fluctuations can induce parametric resonance in axion fields during the QCD phase transition, significantly affecting the predicted axion mass range for dark matter.

Contribution

It introduces a novel mechanism where temperature fluctuations enhance axion production via parametric resonance, shifting the viable mass window for axion dark matter.

Findings

Axion mass window for dark matter is shifted to $10^{-4}-10^{-3}$ eV.

Parametric resonance significantly enhances axion production during the QCD transition.

The canonical axion mass window is displaced to higher, previously unexplored ranges.

Abstract

We demonstrate that dark matter axion production is enhanced through a natural and unavoidable mechanism: primordial temperature fluctuations periodically modulate the axion mass during the QCD phase transition, thereby triggering parametric resonance in axion field evolution. This interplay between parametric resonance and the misalignment mechanism shifts the predicted axion mass window for the observed dark matter abundance to $10^{-4}-10^{-3} \, \text{eV}$, displacing the canonical axion mass window to previously unexplored higher ranges.