Leptogenesis and the Higgs Portal

TL;DR

This paper investigates how Higgs portal couplings to a new scalar singlet influence leptogenesis, revealing new CP-violating decay channels and relaxing constraints on the lightest singlet neutrino's mass.

Contribution

It introduces a model where Higgs portal interactions enable additional CP violation in leptogenesis, especially affecting the $N_2$ decay channels and relaxing the Davidson-Ibarra bound.

Findings

Higgs portal couplings open new CP-violating decay channels.

Leptogenesis can occur with a lighter $N_1$ neutrino than previously constrained.

The model allows for successful leptogenesis with weakly coupled $N_1$.

Abstract

We study the impact on leptogenesis of Higgs portal couplings to a new scalar singlet. These couplings open up additional $CP$-violating decay channels for the higher mass singlet neutrinos $N_2$ and $N_3$. We analyze the simplest case of two-level $N_1-N_2$ leptogenesis, including significant mass hierarchies, in which the $CP$ asymmetry is generated in part by singlet-mediated decays of $N_2$. For these models, provided the lightest singlet neutrino $N_1$ is sufficiently weakly coupled to avoid excessive washout, its mass scale is not directly constrained by the Davidson-Ibarra bound.