Newνconstraints on Majorana mass matrices

We discuss constraints on the three by three Majorana neutrino mass matrix consistent with neutrinoless double {β} decay experiments, neutrino oscillation experiments, and the existence of a 17-keV neutrino. We find that ν_μ and ν_τ must be nearly degenerate, or ν_μ 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.