Detecting axion-like particles at radio frequencies

Dark matter in the form of axion-like particles can decay into monochromatic photons. We investigate the prospects for detection of these signals with radio telescopes. We show that the presence of an ambient radiation field induces a stimulated enhancement of the decay rate. Depending on the environment, this effect can boost the photon signal by several orders of magnitude. We analyze different astrophysical targets, namely dwarf spheroidal galaxies, the Galactic Center and galaxy clusters. For axion-photon couplings allowed by astrophysical and laboratory constraints, the signal is within the reach of next-generation radio telescopes such as the Square Kilometer Array.