Authors Referees APS Members |
January 2008, to be published in Physical Review D1
Sterile neutrinos as the warm dark matter in the type II seesaw model
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 ${\cal N} - 1$ for ${\cal N}$ 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 $M_\nu ^{II} \sim M_\nu ^{I}$. © 2008 The American Physical Society.
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