Sterile neutrinos as dark matter

Abstract

The simplest model that can accommodate a viable nonbaryonic dark matter candidate is the standard electroweak theory with the addition of right-handed (sterile) neutrinos. We consider a single generation of neutrinos with a Dirac mass \ensuremath{\mu} and a Majorana mass M for the right-handed component. If M\ensuremath{\gg}\ensuremath{\mu} (standard hot dark matter corresponds to M=0), then sterile neutrinos are produced via oscillations in the early Universe with energy density independent of M. However, M is crucial in determining the large scale structure of the Universe; for M\ensuremath{\sim}100 eV, sterile neutrinos make an excellent warm dark matter candidate.