  Sterile neutrino with mass of several keV can be the cosmological dark
matter, can explain the observed velocities of pulsars, and can play an
important role in the formation of the first stars. We describe the production
of sterile neutrinos in a model with an extended Higgs sector, in which the
Majorana mass term is generated by the vacuum expectation value of a
gauge-singlet Higgs boson. In this model the relic abundance of sterile
neutrinos does not necessarily depend on their mixing angles, the
free-streaming length can be much smaller than in the case of warm dark matter
produced by neutrino oscillations, and, therefore, some of the previously
quoted bounds do not apply. The presence of the gauge singlet in the Higgs
sector has important implications for the electroweak phase transition,
baryogenesis, and the upcoming experiments at the Large Hadron Collider and a
Linear Collider.
