Non-Unitary Neutrino Propagation From Neutrino Decay
  Neutrino propagation in space-time is not constrained to be unitary if very light states - lighter than the active neutrinos - exist into which neutrinos may decay. If this is the case, neutrino flavor-change is governed by a handful of extra mixing and "oscillation" parameters, including new sources of CP-invariance violation. We compute the transition probabilities in the two- and three-flavor scenarios and discuss the different phenomenological consequences of the new physics. These are qualitatively different from other sources of unitarity violation discussed in the literature. 
Jeffrey M. Berryman, Andr\'e de Gouv\^ea, Daniel Hern\'andez, and   Roberto L. N. Oliveira
hep-ph