BARYOGENESIS FROM A PRIMORDIAL LEPTON ASYMMETRY

There are two ways in which a primordial lepton asymmetry may be turned into a baryon asymmetry at the weak scale. The first is well known in the literature and works in equilibrium. Here we introduce the second, which operates if the electroweak phase transition is first order. Tau leptons are partially reflected off the bubble walls resulting in a hypercharge transport into the symmetric phase. Because leptons do not interact strongly, their thermal length is relatively large and leads to a baryon number consistent with observation. Since the resulting asymmetry is comparable to that produced if the phase transition is second order, we conclude that the baryon number induced by a primordial lepton asymmetry is independent of the way it is processed at the weak scale.