Sterile Neutrinos as the Warm Dark Matter in the Type II Seesaw Model

TL;DR

This paper explores how the type II seesaw mechanism influences the number of sterile neutrinos that can serve as warm dark matter, revealing conditions under which one or all sterile neutrinos may be WDM candidates.

Contribution

It analyzes the impact of the relative magnitude of type II and type I seesaw mass terms on the number of sterile neutrinos as warm dark matter in the model.

Findings

Only one sterile neutrino can be WDM if $M_ u ^{II} extless extless M_ u ^{I}$.

All sterile neutrinos may be WDM if $M_ u ^{II} extgreater extgreater M_ u ^{I}$.

The allowed number of WDM sterile neutrinos varies with the relation between $M_ u ^{II}$ and $M_ u ^{I}$.

Abstract

In the framework of type II seesaw mechanism we discuss the number of sterile right-handed Majorana neutrinos being the warm dark matter (WDM). When the type II seesaw mass term $M_\nu ^{II}$ is far less than the type I seesaw mass term $M_\nu ^{I}$, only one of three sterile neutrinos may be the WDM particle. On the contrary, the WDM particles may contain all sterile neutrinos. If $M_\nu ^{II} \sim M_\nu ^{I}$, the allowed number is not more than $N - 1$ for $N$ sterile neutrinos. It is worthwhile to stress that three different types of neutrino mass spectrum are permitted when $M_\nu ^{II} \gg M_\nu ^{I}$ and $M_\nu ^{II} \sim M_\nu ^{I}$.