Sterile neutrinos produced near the electroweak scale: Mixing angles, MSW resonances, and production rates

We study the production of sterile neutrinos in the region T similar to M-W in an extension beyond the standard model with the seesaw mass matrix originating in Yukawa couplings to Higgs-like scalars with masses and vev's of the order of the electroweak scale. Sterile neutrinos are produced by the decay of scalars and standard model vector bosons. We obtain the index of refraction, dispersion relations, mixing angles in the medium and production rates including those for right-handed sterile neutrinos, from the standard model and beyond the standard model self-energies. For 1 less than or similar to M-W/T less than or similar to 3 we find narrow MSW resonances with k less than or similar to T for both left- and right-handed neutrinos even in absence of a lepton asymmetry in the (active) neutrino sector, as well as very low energy (k/T