Leptogenesis assisted by scalar decays

TL;DR

This paper proposes a scalar decay mechanism to generate lepton asymmetry at lower right-handed neutrino mass scales, effectively overcoming washout effects and broadening leptogenesis viability.

Contribution

Introducing a scalar decay channel to enhance leptogenesis at lower neutrino masses, expanding the parameter space for successful baryogenesis.

Findings

Scalar-assisted leptogenesis reduces the required right-handed neutrino mass scale by 1-3 orders of magnitude.

The mechanism is effective even with strong washout effects.

Leptogenesis can occur at lower temperatures than traditional models.

Abstract

We present a pragmatic approach to lower down the mass scale of right-handed neutrinos in leptogenesis by introducing a scalar decaying to right-handed neutrinos. The key point of our proposal is that the out-of-equilibrium decays of the scalar provide an additional source for right-handed neutrinos and hence the lepton asymmetry. This mechanism works well at low temperatures when the washout of the generated lepton asymmetry is suppressed. Thus, the lepton asymmetry can be effectively produced despite the washout effect is strong or not. Through a comprehensive analysis, we demonstrate that such a scalar-assisted leptogenesis can typically decrease the viable right-handed neutrino mass scale by one to three orders of magnitude.