Formation of the seed black holes: a role of quark nuggets?
  Strange quark nuggets (SQNs) could be the relics of the cosmological QCD
phase transition, and they could very likely be the candidate of cold quark
matter if survived the cooling of the later Universe, although the formation
and evolution of these SQNs depend on the physical state of the hot QGP
(quark-gluon plasma) phase and the state of cold quark matter. We reconsider
the possibility of SQNs as cold dark matter, and find that the formation of
black holes in primordial halos could be significantly different from the
standard scenario. In a primordial halo, the collision between gas and SQNs
could be frequent enough, and thus the viscosity acting on each SQN would
decrease its angular momentum and make it to sink into the center of the halo,
as well as heat the gas. The SQNs with baryon numbers less than $10^{35}$ could
assemble in the center of the halo before the formation of primordial stars. A
black hole could form by merger of these SQNs, and then its mass could quickly
become about $10^3\ M_\odot$ or higher, by accreting the surrounding SQNs or
gas. The black holes formed in this way could be the seeds for the supermassive
black holes at redshift as high as $z\sim 6$.
