Bounds on PBH fraction in a stimulated axion/ALP decay scenario

In this work, we show that stimulated decay of axions or axion-like particles (ALP) in black hole superradiance is an efficient way to find and hunt primordial black holes (PBH). When de Broglie’s wavelength of the axion/ ALP is comparable or larger than the black hole horizon radius, a large population of them accumulates in the surroundings of the black hole. When these axions or ALPs couple to photons, the bosonic cloud decays into radiation 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 ${10}^{-3}\mathrm{e}\mathrm{V}<\mu <1\mathrm{e}\mathrm{V}$, to be consistent with current observations of microwave background light, we found that the fraction of primordial black holes should be smaller than $f_{PBH}<{10}^{-17}$ for primordial black holes with masses within ${10}^{-19}{M}_{\odot }<M_{BH}<{10}^{-7}{M}_{\odot }$.