NEUTRINO OSCILLATIONS FROM DIRAC AND MAJORANA MASSES

We present a scenario of neutrino masses and mixing angles. Each gener ation includes a sterile right-handed neutrino in addition to the usua l left-handed one. We assume a hierarchy in their Dirac masses similar to, but much larger than, the hierarchies in the quarks and charged l eptons. In addition, we include a Majorana mass term for the sterile n eutrinos only. These assumptions prove sufficient to accommodate scale s of mass differences and mixing angles consistent with all existing n eutrino oscillation data.