Lowering the scale of fermion triplet leptogenesis with two Higgs doublets

TL;DR

This paper explores how two-Higgs-doublet models can significantly lower the energy scale required for successful leptogenesis via fermion triplet decay, making the process more accessible within particle physics models.

Contribution

It demonstrates that introducing two Higgs doublets can reduce the lower bound of triplet fermion mass for leptogenesis from 10^10 GeV to 10^7 GeV, especially when flavor effects are considered.

Findings

Lower bound on triplet mass reduced to 10^7 GeV.

Flavor effects further decrease the bound by an order of magnitude.

Compatibility with naturalness bounds discussed.

Abstract

In this paper, we consider the possibility of generating the observed baryon asymmetry of the Universe via leptogenesis in the context of triplet fermion mediated type-III seesaw model of neutrino mass. With a hierarchical spectrum of the additional fermions, the lower bound on the lightest triplet mass is $\sim 10^{10} {\rm~GeV}$ for successful leptogenesis, a couple of orders higher than that of the type-I case. We investigate the possibility of lowering this bound in the framework of two-Higgs-doublet models. We find that the bounds can be lowered down to $10^7$ GeV for a hierarchical spectrum. If we include the flavor effects, then a further lowering by one order of magnitude is possible. We also discuss if such lowering can be compatible with the naturalness bounds on the triplet mass.