New<i>ν</i>constraints on Majorana mass matrices

Abstract

We discuss constraints on the three by three Majorana neutrino mass matrix consistent with neutrinoless double \ensuremath{\beta} decay experiments, neutrino oscillation experiments, and the existence of a 17-keV neutrino. We find that ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ must be nearly degenerate, or ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ must be heavier than 250 keV. A new parametrization of the mixing in the neutrino sector is proposed. We give a simple example of a mass matrix which satisfies all constraints.