QCD Axion Dark Matter from a Late Time Phase Transition

TL;DR

This paper explores a scenario where QCD axion dark matter is produced after a late-time Peccei-Quinn phase transition, resulting in abundant axions that can account for dark matter even at lower decay constants, with potential observable effects on structure formation and rare Kaon decays.

Contribution

It introduces a novel mechanism for axion production via a late phase transition, expanding viable parameter space for axion dark matter models.

Findings

Abundant axion production after late phase transition.

Dark matter abundance achievable at decay constants below 10^{11} GeV.

Potential observable effects on structure formation and rare Kaon decays.

Abstract

We investigate the possibility that the Peccei-Quinn phase transition occurs at a temperature far below the symmetry breaking scale. Low phase transition temperatures are typical in supersymmetric theories, where symmetry breaking fields have small masses. We find that QCD axions are abundantly produced just after the phase transition. The observed dark matter abundance is reproduced even if the decay constant is much lower than $10^{11}$ GeV. The produced axions tend to be warm. For some range of the decay constant, the effect of the predicted warmness on structure formation can be confirmed by future observations of 21 cm lines. A portion of parameter space requires a mixing between the Peccei-Quinn symmetry breaking field and the Standard Model Higgs, and predicts an observable rate of rare Kaon decays.