Abstract :
We follow a minimalistic approach to neutrino masses, by introducing a single heavy singlet N into the standard model (or supersymmetric standard model) with a heavy Majorana mass M, which couples as a single right-handed neutrino in a Dirac fashion to leptons, and induces a single light see-saw mass mν∼5×10−2 eV, leaving two neutrinos massless. This trivial extension to the standard model may account for the atomospheric neutrino data via νμ→ντ oscillations with near maximal mixing angle θ23∼π/4 and Δmμτ2∼2.5×10−3 eV2. In order to account for the solar neutrino data the model is extended to SUSY GUT/ string-inspired type models which can naturally yield an additional light tau neutrino mass mντ∼few×10−3 eV leading to νeL→(cosθ23νμL−sinθ23ντL) oscillations with Δme12∼10−5 eV2 and a mixing angle sin22θ1≈10−2 in the correct range for the small angle MSW solution to the solar neutrino problem. The model predicts νeL→(sinθ23νμL+cosθ23ντL) oscillations with a similar angle but a larger splitting Δme22∼2.5×10−3 eV2.
