Cowsik's argument on neutrino lifetimes must be modified if the neutrinos are sufficiently massive. Neutrinos of masses greater than 100-700 keV and which decay into much lighter neutrinos and a photon are consistent with astrophysical data on white dwarf stars. Experimental muon-neutrino mass limits combined with our arguments require masses of less than a few eV (and lifetimes greater than ${10}^{22}$ sec), or in the range ∼100-500 keV.

• Received 7 March 1978

DOI:https://doi.org/10.1103/PhysRevD.19.2215