The total merger rate of primordial black holes

The merger rate of primordial black hole (PBH) binaries is important for understanding the source population of the merging black hole binaries observable through gravitational waves (GWs) and also for constraining the possible contribution of PBHs to dark matter. In the literature, the merger rate of PBHs is calculated analytically, assuming that PBH binaries stay in isolation (i.e., are unperturbed) and evolve solely via GW emission during their entire lifetime. However, if some or all of dark matter consists of PBHs, then as cosmic structures grow, PBH binaries and single PBHs fall inside dark matter halos. In those halos, the PBH binary interactions with their environment significantly affect the subsequent evolution of their orbital properties.

In this talk, I will present a numerical framework that accurately calculates the total PBH merger rate by combining the evolution of isolated binaries outside halos with the dynamics of binaries inside halos. In our work, we have found that the isolated binary channel is suppressed at low redshifts and dynamical interactions, such as binary-single interactions in halos, significantly reshape the merger rate evolution with time, accelerating some mergers. Our results are important for accurate constraints on the PBH abundance from GW observations.