The (ir)Relevance of Initial Conditions in Soft Leptogenesis

Abstract

We explore how the initial conditions affect the final lepton asymmetry in Soft Leptogenesis. It has been usually assumed that the initial state is a statistical mixture of sterile sneutrinos and anti-sneutrinos with equal abundances. We calculate the lepton asymmetry due to the most general initial mixture. The usually assumed equal mixture produces a small, but sufficient, lepton asymmetry which is proportional to the ratio of the supersymmetry breaking scale over the Majorana scale. A more generic mixture, still with equal contents of sneutrinos and anti sneutrinos, yields an unsuppressed lepton asymmetry. Mixtures of non equal contents of sneutrinos and anti sneutrinos result in a large lepton asymmetry too. While these results establish the robustness of Soft Leptogenesis and other mixing based mechanisms, they also expose their lack of predictive power.