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

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 $M_{\nu }^{II}\sim M_{\nu }^I$.

Comments: 8 pages