A recent article by Avi Friedlander, Ningqiang Song, and Aaron C. Vincent proposes a new mechanism for the gravitational production of dark matter that does not rely on non-gravitational interactions with the Standard Model or specific inflationary physics. The authors suggest that if the temperature of the hot thermal plasma in the early universe
was within a few orders of magnitude of the Planck scale, then microscopic black holes could have formed from particle collisions in the plasma. Under minimal assumptions of a high reheat temperature and semiclassical black hole dynamics, this process could have produced the observed relic abundance of dark matter for a particle mass in the range of 100 keV to MPl.
Unlike most previous attempts to explain the relic abundance of dark matter, this scenario does not require any non-gravitational portal between the Standard Model and the dark sector, which could lead to signatures in the laboratory from scattering, annihilation, or production at colliders. The authors use analytic expressions to calculate the relic abundance of dark matter and the abundance of stable Planckeons, which could be the end result of black hole evaporation. They find that the lowest order analytic approximation underestimates the relic abundance, but the error is significantly reduced for lower reheating temperatures, as is needed to produce the correct relic abundance for fermionic dark matter with mdm = 1 GeV. The authors conclude that their proposed mechanism provides a novel way to produce dark matter that is consistent with standard Big Bang cosmology.