Stability of Neutrinos in the Singlet Majoron Model

Abstract

We show that there is no one-loop enhancement of the rate for a light neutrino to decay into a lighter neutrino plus a majoron, contrary to a recent claim. Thus the light neutrinos must satisfy the cosmological bound of having masses less than 35 eV in the singlet majoron model, or else violate the constraint imposed by galaxy formation. In the latter case, $\nu_\tau$ could have a mass between 40 and 500 keV, while satisfying all other cosmological constraints.