Dark matter from hot big bang black holes

If the temperature of the hot thermal plasma in the Early Universe was within a few orders of magnitude of the Planck scale $M_{\mathrm{P}\mathrm{l}}$, then the hoop conjecture predicts the formation of microscopic black holes from particle collisions in the plasma. Although these evaporated instantly, they would have left behind a relic abundance of all stable degrees of freedom which couple to gravity. Here we show that, upon minimal assumptions of a high reheat temperature and semiclassical black hole dynamics, this process could have produced the relic abundance of dark matter observed today for a particle mass anywhere in the range of $100\mathrm{k}\mathrm{e}\mathrm{V}\lesssim m_{dm}<M_{\mathrm{P}\mathrm{l}}$, though it could be subdominant to graviton-mediated freeze-in above $m_{dm}\sim$ MeV. The production mechanism does not rely on any additional assumptions about non-gravitational dark matter-Standard Model interaction.