Neutrino oscillation seems to have as one of its prerequisites the fact that the flavour eigenstates differ from the mass eigenstates, so the time-dependent Schrödinger equation applies. Can a neutrino "drop" into the lowest mass eigenstate (which is also the lowest eigenstate of the Hamiltonian?) and stop oscillating? I'm aware that this is a very unlikely process. The simplest Feynman diagram for the neutrino to get rid of the energy seems to involve three vertices, a W propagator and emission of a photon. Plus, there's a huge time dilation. But will it eventually happen? And could this be detected, in principle, by measuring flavour ratios from a faraway neutrino source?