Comparison of various extensions of the QRPA formalism for the double-beta decay.

We have used a self-consistent version of the BCS + RQRPA method for a systematic study of the double-beta decay of medium-heavy nuclei with 70 ≤ A ≤100. The results have been compared with the previously used approaches, namely the QRPA and the RQRPA approximations. We have shown that inclusion of the quasiparticle correlations at the BCS level reduces ground state correlations in the particle–particle channel of the proton–neutron interaction, resulting in a systematic reduction of the double-beta-decay matrix elements. We also simplified the RQRPA equations significantly obtaining a low-dimensioned set of linear equations for the quasiparticle densities. [ABSTRACT FROM AUTHOR]