Mergers of maximally charged primordial black holes

Near-extremal primordial black holes stable over cosmological timescales may constitute a significant fraction of the dark matter. Due to their charge, the coalescence rate of such black holes is enhanced inside clusters, and the nonextremal merger remnants are prone to Hawking evaporation. We demonstrate that if these clusters of near-extremal holes contain a sufficient number of members to survive up to low redshift, the hard photons from continued evaporation begin to dominate the high energy diffuse background. We find that the diffuse photon flux can be observed for a monochromatic mass spectrum of holes lighter than about 10(12) g. We place upper bounds on their abundance respecting the current bounds set by gamma ray telescopes. Furthermore, the gravitational wave background induced at the epoch of primordial black hole formation may be detectable by future planned and proposed ground-based and space-borne gravitational wave observatories operating in the mHz to kHz frequency range and can be an important tool for studying light charged primordial black holes over masses in the range of 10(12)-10(19) g.

Automated summary

Near-extremal primordial black holes stable over cosmological timescales may constitute a significant fraction of dark matter. If clusters of these black holes contain a sufficient number of members to survive up to low redshift, the high energy diffuse background can be dominated by the photons from continued evaporation. In addition, the gravitational wave background induced at the epoch of primordial black hole formation can be detected and used to study light charged primordial black holes in a certain mass range.