2026/07/20 by Duncan Rocha, Gordan Krnjaic, Matthew J. Baldwin
#hep-ph
The cosmic axion background (CaB) is a hypothetical population of relativistic axions produced in the early universe. If the CaB is produced from dark matter decays, the axions in this population can convert to photons in the magnetic fields of cosmological filaments, resulting in an isotropic gamma ray background flux. We present new indirect detection constraints on the axion mass and axion-photon coupling, for GeV-TeV dark matter with a decay lifetime below 1030 sec, by comparing this flux against experimental data. We exclude significant parameter space for axion masses below 10-5~eV for a broad range of dark matter masses and lifetimes, assuming conservative filament magnetic field strengths (∼ 1 nG). For large filament fields (∼ 100 nG), our strategy also constrains a portion of the QCD-axion parameter space for TeV-scale dark matter masses.