SUPPRESSION OF THE 2-NEUTRINO BETA-BETA-DECAY IN A PARTICLE NUMBER PROJECTED QUASI-PARTICLE RANDOM PHASE APPROXIMATION

Two-neutrino beta-beta-decay rates of Ge-76, Se-82, Kr-86, Cd-114 and Te-128, Te-130 are calculated in a fully number-projected quasiparticle random-phase approximation. The model is based on the restoration of particle-number symmetries both at the level of quasiparticle and phonon excitations. Calculations are performed using a realistic nucleon-nucleon interaction. The effects of ground-state correlations and of the projection on good particle number are discussed in connection to the strong suppression of 2-upsilon-beta-beta matrix elements. It is found that the full particle number projection yields non-vanishing matrix elements in the neighborhood of critical values of the coupling constant g(pp) which renormalizes the particle-particle interaction.