The (ir)Relevance of Initial Conditions in Soft Leptogenesis

TL;DR

This paper investigates how different initial conditions in Soft Leptogenesis influence the resulting lepton asymmetry, revealing the process's robustness but also its limited predictive power due to initial state sensitivities.

Contribution

It provides a comprehensive calculation of lepton asymmetry for general initial mixtures, challenging the assumption of equal initial states and highlighting the impact of initial conditions.

Findings

Equal initial mixtures produce sufficient asymmetry proportional to supersymmetry and Majorana scales.

Generic equal mixtures yield unsuppressed asymmetry, confirming robustness.

Non-equal mixtures lead to large asymmetries, exposing sensitivity to initial conditions.

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.