Hidden axion dark matter decaying through mixing with QCD axion and the 3:5 keV X-ray line

Tetsutaro Higaki, Naoya Kitajima, Fuminobu Takahashi

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


Hidden axions may be coupled to the standard model particles through a kinetic or mass mixing with QCD axion. We study a scenario in which a hidden axion constitutes a part of or the whole of dark matter and decays into photons through the mixing, explaining the 3:5 keV X-ray line signal. Interestingly, the required long lifetime of the hidden axion dark matter can be realized for the QCD axion decay constant at an intermediate scale, if the mixing is sufficiently small. In such a two component dark matter scenario, the primordial density perturbations of the hidden axion can be highly non-Gaussian, leading to a possible dispersion in the X-ray line strength from various galaxy clusters and near-by galaxies. We also discuss how the parallel and orthogonal alignment of two axions affects their couplings to gauge fields. In particular, the QCD axion decay constant can be much larger than the actual Peccei-Quinn symmetry breaking.

Original languageEnglish
Article number004
JournalJournal of Cosmology and Astroparticle Physics
Issue number12
Publication statusPublished - 2014 Dec 1
Externally publishedYes


  • Axions
  • Dark matter theory
  • Particle physics - Cosmology connection

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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