Axion dark matter with explicit Peccei-Quinn symmetry breaking in the axiverse

Understand

It was shown that the required high quality of the Peccei-Quinn (PQ) symmetry can be a natural outcome of the multiple QCD axions model.

• In the axiverse, a hypothetical mass mixing between the QCD axions and axion-like particles (ALPs) can occur, which leads to an interesting phenomenon called the level crossing.
• In this paper, we investigate this mass mixing between one QCD axion and one ALP with the explicit PQ symmetry breaking in the early Universe.
• The dynamics of the axions and their cosmological evolutions when the level crossing occurs in this scenario are studied in detail.