The SNO Solar Neutrino Data , Neutrinoless Double Beta - Decay and Neutrino Mass Spectrum

Assuming 3-ν mixing and massive Majorana neutrinos, we analyze the implications of the results of the solar neutrino experiments, including the latest SNO data, which favor the LMA MSW solution of the solar neutrino problem with tan 2 θ ⊙ < 1, for the predictions of the effective Majorana mass |< m >| in neutrinoless double beta-decay. Neutrino mass spectra with normal mass hierarchy, with inverted hierarchy and of quasi-degenerate type are considered. For cos 2θ ⊙ ∼ > 0.26, which follows (at 99.73% C.L.) from the SNO analysis of the solar neutrino data, we find significant lower limits on |< m >| in the cases of quasi-degenerate and inverted hierarchy neutrino mass spectrum, |< m >| ∼ > 0.035 eV and |< m >| ∼ > 8.5 × 10 −3 eV, respectively. If the spectrum is hierarchical the upper limit holds |< m >| ∼ < 8.2 × 10 −3 eV. Correspondingly, not only a measured value of |< m >| = 0, but even an experimental upper limit on |< m >| of the order of few×10 −2 eV can provide information on the type of the neutrino mass spectrum; it can provide also a significant upper limit on the mass of the lightest neutrino m 1. A measured value of |< m >| ∼ > 0.2 eV, combined with data on neutrino masses from the 3 H β−decay experiment KATRIN, might allow to establish whether the CP-symmetry is violated in the lepton sector.