Baryons from evaporating primordial black holes

Abstract: We propose a new pathway to the baryon asymmetry in which small primordial black holes (PBHs) act as localized, short-lived baryogenesis engines after the electroweak phase transition (EWPT). Hawking emission from evaporating PBHs deposits energy into the surrounding plasma, creating over-pressured hot spots that drive near-acoustic shock fronts. Inside these fronts the Higgs expectation value is driven to the symmetric phase while remaining broken outside, yielding moving interfaces that source chiral charge; active sphalerons in the restored regions then convert this into baryon number. We compute the time-dependent Hawking power across Standard Model species, estimate the microscopic Landau–Pomeranchuk–Migdal thermalization length that sets the initial hot-spot size, and solve the hydrodynamics of the expanding front. Adapting electroweak baryogenesis methods to moving walls, we derive the resulting baryon yield for PBH populations with realistic time-dependent mass functions resulting from critical collapse theory. Crucially, the mechanism supplies the needed out-of-equilibrium dynamics without requiring new physics to render the EWPT first order.