Two 17-keV Majorana Neutrinos?

Abstract

A recent observation of a 17-keV neutrino in tritium beta decay can be incorporated into the standard model with just three light neutrinos. Constraints on neutrino masses suggest that the lepton mass matrices have an approximate global symmetry which results in two of the three neutrinos having masses near 17 keV. A prediction for the mixing angle in ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillations is made. Cosmological constraints on the 17-keV neutrino are discussed. Models with majorons or familons are found to be attractive possibilities.