Solar and atmospheric four neutrino oscillations

We present an analysis of the neutrino oscillation solutions of the solar and atmospheric neutrino problems in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones and the mass spectra present two separated doublets. Such scenarios allow for simultaneous transitions of solar n e ,a s well as atmospheric n m , into active and sterile neutrinos controlled by the additional mixing angles q 23 and q 24 , and they contain as limiting cases the pure solar n e-active and n e-sterile neutrino oscillations, and the pure atmospheric n m!n s and n m!n t oscillations, respectively. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations from the combined analysis. Our results show that, although the Super-Kamiokande data disfavor both the pure n m!n s atmospheric channel and the pure n e!n s solar channel, the result from the combined analysis still favors close-to-pure active and sterile oscillations and disfavors oscillations into a near-maximal active-sterile admixture.