Evidence for primordial black hole dark matter from LIGO/Virgo merger rates

Understand

The LIGO/Virgo collaboration has by now observed or constrained the gravitational merger rates of different classes of compact objects.

• We consider the possibility that the bulk of these mergers are primordial black hole (PBH) mergers of PBHs formed during the QCD epoch making up the entirety of the dark matter.
• Having shown in a companion paper that mergers due to the initial binary population formed in the early Universe are likely negligible, we compute current merger rates in PBH clusters in which the typical PBH resides.
• We consider two scenarios: (i) the PBH mass function dictated by the QCD equation of state and (ii) the PBH mass function dictated by the existence of a peak in the inflationary perturbation spectrum.