Majorana neutrino masses from neutrinoless double beta decay and cosmology

When three Majorana neutrinos describe the solar and atmospheric neutrino data via oscillations, a nonzero measurement of neutrinoless double beta (0νββ) decay can determine the sum of neutrino masses ∑mν if the solar solution has small-angle mixing, and place a lower bound on ∑mν for large-angle solar mixing. If in addition a nonzero ∑mν is deduced from cosmology, the neutrino mass spectrum may be uniquely specified for some ranges of neutrino parameters. For ∑mν>0.75 eV, the small-angle solar solution is excluded by the current upper limit on neutrinoless double beta decay. In models with maximal solar mixing the CP phases of the neutrinos may be strongly constrained by stringent upper bounds on 0νββ decay.