Electroweak Baryogenesis in a Cold Universe

We discuss the possibility of generating the baryon asymmetry of the Universe when the temperature of the Universe is much below the electroweak scale. In our model the evaporation of primordial black holes or the decay of massive particles re-heats the surrounding plasma to temperatures above the electroweak transition temperature leading to the restoration of electroweak symmetry locally. The symmetry is broken again spontaneously as the plasma cools and a baryon asymmetry is generated during the phase transition. This mechanism generates sufficient asymmetry for a second order electroweak phase transition. For a first order phase transition, sufficient asymmetry is generated if viscous effects slow down the heated plasma as it moves away from the black hole. In our scenario there is no wash-out of the asymmetry after the phase transition as the plasma rapidly cools to lower temperatures thereby shutting off the sphaleron processes.

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