# Low scale leptogenesis in a hybrid model of the scotogenic type I and III seesaw

## TL;DR

This paper proposes a hybrid model combining scotogenic type I and III seesaw mechanisms, demonstrating that low-scale leptogenesis is feasible with a singlet fermion extension, achieving successful leptogenesis at masses as low as 10^4 GeV.

## Contribution

The study introduces a hybrid scotogenic model with a singlet fermion extension, enabling low-scale leptogenesis despite the gauge interactions of triplet fermions.

## Key findings

- Leptogenesis can occur successfully at low singlet fermion masses (~10^4 GeV).
- Introducing a singlet fermion allows out-of-equilibrium conditions for leptogenesis.
- The model addresses the equilibrium issue of triplet fermions in pure type III seesaw.

## Abstract

The scotogenic type I and type III seesaw models are good candidates to explain the existence of neutrino masses and dark matter simultaneously. However, since triplet fermions have SU(2) gauge interaction, they cannot be out of equilibrium before the electroweak symmetry breaking. Thus, leptogenesis seems to be difficult within a framework of the pure type III seesaw model. Some extension seems to be required to solve this fault. A model extended by introducing a singlet fermion could be such a simple example. If the singlet fermion is in the thermal equilibrium even for its extremely small neutrino Yukawa coupling, leptogenesis could be shown to occur successfully for a rather low mass of the singlet fermion. The required mass could be lowered to $10^4$~GeV.