Enhanced extragalactic photon flux by PBH in a stimulated axion/ALP decay scenario

In this work, we show that stimulated decay of axions or axion-like particles in black hole superradiance is an efficient way to find and hunt primordial black holes. When de Broglie’s wavelength of the axion/ALP is comparable or larger than the black hole horizon radius, a large population of such particles accumulates in the surroundings of the black hole. When these axions/ALPs couple to photons, the bosonic cloud decays into photon pairs, generating intense stimulated radiation emission that contributes to the X-ray, visible light, and radio wave background flux that can exceed current observational limits measured at Earth. If the masses are in the interval of 10 − 3 eV < μ < 1 eV , to be consistent with current observations of microwave background light, we found that the fraction of primordial black holes should be smaller than f P B H < 10 − 17 for PBHs with masses within 10 − 13 M ⊙ < M B H < 10 − 7 M ⊙ .