Update on Solar and Atmospheric Four-Neutrino Oscillations

Abstract

In this talk we present the update (including the recent SNO results) of our 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 $ν_e$, as well as atmospheric $ν_μ$, into a combination of active and sterile neutrinos. 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 disfavour both the pure $ν_μ\toν_s$ atmospheric channel and, in combination with SNO, the pure $ν_e\toν_s$ solar channel, the result from the combined analysis still favours close-to-pure active and sterile oscillations and disfavours oscillations into a near-maximal active-sterile admixture.