Astrophysical Appearance of Primordial Black Holes

Interest to astrophysical evidence for primordial black holes (PBHs) formed in the early Universe from initial cosmological perturbations has increased after the discovery of coalescing binary black holes with masses more than dozen solar ones by gravitational-wave (GW) observatories. We briefly discuss increasing evidence that PBHs can provide some fraction of detected merging binary BHs and can be related to an isotropic stochastic GW background recently discovered by pulsar timing arrays. We focus on PBHs with log-normal mass spectrum originated from isocurvature perturbations in the modified Affleck–Dine baryogenesis scenario by Dolgov and Silk (1993). We show that almost equal populations of astrophysical binary BHs from massive binary evolution and binary PBHs with log-normal mass spectrum can describe both the observed chirp mass distribution and effective spin—mass ratio anti-correlation of the LVK binary BHs.