Consistent BCS+RQRPA formalism with application to the double beta decay

A new consistent analysis of the renormalized proton--neutron quasiparticle random phase approximation based on the simultaneous recalculation of the one--body density matrix and the pairing tensor has been used to study the double beta decay. We demonstrated that inclusion of the quasiparticle correlations at the BCS level reduces the ground state correlations in the particle--particle channel of the proton--neutron interaction. We also simplified the RQRPA equations significantly obtaining a low--dimensioned set of linear equations for the quasiparticle densities. The formalism was applied to the double beta decay in ^{76}Ge.