Four-neutrino mixing solutions of the atmospheric neutrino anomaly

Solutions to the atmospheric neutrino anomaly which smoothly interpolate between nu_mu -> nu_tau and nu_mu -> nu_s oscillations are studied. It is shown that, although the Super-Kamiokande data disfavor the pure nu_mu -> nu_s channel, one cannot exclude sizable amplitude for the nu_mu -> nu_s channel in addition to nu_mu -> nu_tau oscillations.Comment: Talk given at Europhysics Neutrino Oscillation Workshop (NOW2000), Conca Specchiulla, Otranto, Lecce, Ita, 9-16 Sep 200