QRPA AND RQRPA CALCULATIONS OF NEUTRINOLESS DOUBLE-BETA DECAY BEYOND THE POINT OF COLLAPSE

Calculations of neutrinoless double beta decay (0 nu beta beta decay) by the methods relying on standard quasiparticle random-phase approxim ation (QRPA) show a sensitivity of nuclear matrix elements to the part icle-particle component of the residual interaction of the nuclear Ham iltonian. Extensions of the standard QRPA, such as renormalization of particle-particle forces that takes into account the Pauli exclusion p rinciple (renormalized QRPA, abbreviated as RQRPA by convention), and inclusion of proton-neutron pairing (full renormalized QRPA, commonly known as full RQRPA) offer a stable solution in the physically accepta ble region of particle-particle strengths. In particular, calculations of the 0 nu beta beta decay of Ge-76, Mo-100, Cd-116, Te-128, and Xe- 136 show that, if a large model space is used, the sensitivity of nucl ear matrix elements to the choice of particle-particle force is elimin ated, in which case more accurate values on the effective neutrino mas s can be deduced.