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
non-extremal 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 $10^{13}\rm g$. 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 $\rm
10^{13}g - 10^{19}g$.
