Neutrino decay and atmospheric neutrinos

We reconsider neutrino decay as an explanation for atmospheric neutrino observations. We show that if the mass-difference relevant to the two mixed states νμ and ντ is very small (<10−4 eV2), then a very good fit to the observations can be obtained with decay of a component of νμ to a sterile neutrino and a Majoron. We discuss how the K2K and MINOS long-baseline experiments can distinguish the decay and oscillation scenarios.