Multi-messenger Probes of Asteroid Mass Primordial Black Holes: Superradiance Spectroscopy, Hawking Radiation, and Microlensing

Superradiance provides a unique opportunity for investigating dark sectors as well as primordial black holes (PBHs), which themselves are candidates for dark matter (DM) over a wide mass range. Using axion-like particles (ALPs) as an example, we show that line signals emerging from a superradiated ALP cloud combined with Hawking radiation from PBHs in extragalactic and galactic halos, along with microlensing observations lead to complementary constraints on parameter space combinations including the ALP-photon coupling, ALP mass, PBH mass, and PBH DM fraction, fPBH. For the PBH asteroid mass range ~10¹⁶-10²²~ g, where PBHs can provide the totality of DM, we demonstrate that ongoing and upcoming observations such as SXI, JWST, and AMEGO-X will be sensitive to possible line and continuum signals, respectively, providing probes of previously inaccessible regions of fPBH parameter space. Further complementarity from a stochastic gravitational-wave background emerging from the PBH formation mechanism is also considered.