Naturally light sterile neutrinos

A simple model to accommodate light sterile neutrinos naturally with large mixing with the usual neutrinos has been proposed. The standard model gauge group is extended to include an ${\mathrm{SU}\left(2\right)\mathrm{}}_S$ gauge symmetry. Heavy triplet Higgs scalars give small masses to the left-handed neutrinos, while a heavy doublet Higgs scalar mixes with the sterile neutrinos of the same order of magnitude. We then present a simple form of the neutrino mass matrix, which may originate from this scenario and can explain the solar neutrino deficit, the atmospheric neutrino deficit, the LSND data, and the hot dark matter. The lepton number is violated through decays of the heavy triplet Higgs scalars, which generate the lepton asymmetry of the universe, which in turn generates a baryon asymmetry of the universe.