Majorana Neutrinos, CP-Violation, Neutrinoless Double-Beta and Tritium-Beta Decays

If the present or upcoming searches for neutrinoless double β− ((ββ)0ν -) decay give a positive result, the Majorana nature of massive neutrinos will be established. From the determination of the value of the (ββ)0ν -decay effective Majorana mass parameter (|| ), it would be possible to obtain information on the type of neutrino mass spectrum. Assuming 3-ν mixing and massive Majorana neutrinos, we discuss the information a measurement of, or an upper bound on, || can provide on the value of the lightest neutrino mass m1. With additional data on the neutrino masses obtained in H β−decay experiments, it might be possible to establish whether the CP-symmetry is violated in the lepton sector. This would require very high precision measurements. If CP-invariance holds, the allowed patterns of the relative CP-parities of the massive Majorana neutrinos would be determined.