No abstract

1 It is worth mentioning that there are a number of different local measurements, nearly all of which find values of H 0 larger than observed by Planck (see e.g. [38]). Among the more robust of these was a recent attempt to re-calibrate the type-Ia SN distances using the tip of the red giant branch (TRGB) [39]. Using this calibration, [39] inferred H 0 = 69.8 ± 1.9 km/s/Mpc, consistent at the ∼ 2σ level with both the CMB and other local mea-arXiv:1909.04044v1 [astro-ph.CO]

Assuming axion-like particles account for the entirety of the dark matter in the Universe, we study the possibility of detecting their decay into photons at radio frequencies. We discuss different astrophysical targets, such as dwarf spheroidal galaxies, the Galactic Center and halo, and galaxy clusters. The presence of an ambient radiation field leads to a stimulated enhancement of the decay rate; depending on the environment and the mass of the axion, the effect of stimulated emission may amplify the photon flux by serval orders of magnitude. For axion-photon couplings allowed by astrophysical and laboratory constraints (and possibly favored by stellar cooling), we find the signal to be within the reach of next-generation radio telescopes such as the Square Kilometer Array.