Majorana neutrinos, neutrino mass spectrum, CP violation, And neutrinolessdouble beta decay. II. Mixing of four neutrinos - art. no. 113003

Assuming four-neutrino mixing and massive Majorana neutrinos, we study the implications of neutrino oscillation solutions of the solar and atmospheric neutrino problems, of the results of the Liquid Scintillation Neutrino Det ector (LSND) experiment and of the constraints on neutrino oscillations, ob tained in reactor and accelerator experiments, for the predictions of the e ffective Majorana mass in neutrinoless double beta ((beta beta)(0 nu)-) dec ay,\[m]\. All four-neutrino mass spectra compatible with the existing neutr ino mass and oscillation data are considered: 2 + 2A,B and 3 + 1A,B,C. The general case of CP nonconservation is investigated. The predicted values of \[m]\ depend strongly on the value of the lightest neutrino mass m(1), on the type of the neutrino mass spectrum, on the LSND neutrino mass-squared d ifference Deltam(SBL)(2) on the solution of the solar neutrino problem, as well as on the values of the three Majorana CP-violating phases, present in the lepton mixing matrix. If CP invariance holds, \[m]\ is very sensitive to the values of the relative CP parities of the massive Majorana neutrinos . We also analyze in detail the question of whether a measurement of \[m]\ 0.01 eV in the next generation of (beta beta)(0 nu)-decay experiments (NEMO 3, CUORE, EXO, and GENIUS), combined with the data from the solar, atmosphe ric, reactor and accelerator neutrino oscillation experiments and from the future neutrino mass H-3 beta -decay experiment KATRIN would allow us, and under what conditions, (i) to determine the absolute values of the neutrino masses and thus the neutrino mass spectrum, and (ii) to establish the exis tence of CP violation in the lepton sector. We have pointed out, in particu lar, that the 2 + 2A and 3 + 1A spectra can be critically tested by the KAT RIN experiment. The latter, in particular, can provide information on the v alue of the lightest neutrino mass m(1) in the cases of the spectra 2+2A, 3 + 1 A, 3 + 1B, and 3 + 1C. For these neutrino mass spectra there exists a direct relation between \[m]\ or m(1) and the neutrino mass measured in H-3 beta decay, m(nue), and the measurement of \[m]\ greater than or similar t o 0.01 eV and of m(nue) greater than or similar to0.4 eV will provide the u nique possibility to determine the absolute values of all four neutrino mas ses and to obtain information on CP violation in the lepton sector.