Impacts of Primordial Black Holes in the Early Universe

The work presented in this thesis draws back the curtain on the physics of the primordial universe by leveraging Primordial Black Holes (PBHs) as cosmological probes. The violent deaths of ultralight PBHs are shown to severely inhibit leptogenesis, alter the sphaleron freeze-out temperature and provide an opportunity to rule out models of leptogenesis which would otherwise evade direct detection experiments for effective eternity. Turning to the extreme temperature gradients of hot spots, the evolution and formation of hot spots was considered in an expanding background for the first time, and a formalism treating the propagation of Hawking radiation was introduced. Upon addressing the previously unexplored effects of hot spots on Hawking radiation, it was discovered that hot spots can support successful leptogenesis after sphaleron freeze-out, and efficiently absorb radiated Dark Matter. These examples hint at an intricate, rich tapestry of physics in hot spots.