Four-neutrino oscillation solutions of the atmospheric neutrino anomaly

Abstract

In the context of neutrino scenarios characterized by four (three active plus one sterile) neutrino species and by mass spectra with two separated doublets, we analyze solutions to the atmospheric neutrino anomaly which smoothly interpolate between ν_μ-->ν_τand ν_μ-->ν_s oscillations. We show that, although the Super-Kamiokande data disfavor the pure ν_μ-->ν_s channel, they do not exclude its occurrence, with sizable amplitude, in addition to the ν_μ-->ν_τchannel. High energy muon data appear to be crucial in assessing the relative amplitude of active and sterile neutrino oscillations. It is also qualitatively shown that such atmospheric νsolutions are compatible with analogous solutions to the solar neutrino problem, which involve oscillations of ν_e in both sterile and active states.