Speaker
Description
Light primordial black holes (PBHs) can briefly dominate the energy density of the early universe before evaporating via Hawking radiation, generically producing any sufficiently light degree of freedom in the process, including photophilic axion-like particles (ALPs). These ALPs subsequently decay to photons, injecting electromagnetic energy into the cosmic plasma at epochs ranging from BBN through recombination and beyond. In this talk I will present a comprehensive analysis of the resulting cosmological signatures across the (m_a,g_aγγ) parameter space. Combining the full Hawking emission spectrum with the subsequent ALP cosmology, we derive constraints from BBN, CMB μ and y-type spectral distortions, and the diffuse extragalactic photon background, and identify the regions of ALP parameter space excluded once a PBH-dominated era is assumed. A PBH-dominated phase substantially enhances the predicted signal relative to scenarios where PBHs are subdominant, opening sensitivity to ALP couplings well below those probed by helioscopes and stellar cooling, including regions motivated by QCD axion and various ALP constructions. I will quantify the projected reach of PIXIE-class spectral distortion mission, discuss how the signal depends on the PBH mass spectrum and the duration of the matter-dominated phase, and outline the complementarity between these cosmological probes and laboratory and astrophysical ALP searches.