Double-β-decay rates within a second quasi-random-phase approximation

Summary

A second QRPA procedure is employed to perform calculations of theM ^2ν_GT matrix elements for several double-β transitions. It is found that higher-order QRPA corrections display a weak dependence on particle-particle strengthg _pp and, in the physical region (aroundg _pp=1.0), they become important by comparison with QRPA predictions. It turns out that further investigations of the higher QRPA corrections could be illuminating to obtain more stable and reliable values forM ^2ν_GT matrix elements in this region, where they are very sensitive to the particle-particle strength. Further, we have studied the influence that higher-order QRPA corrections have on single-β transitions which enter the double-β-decay rates and we have also computed Gamow-Teller matrix elements for double-β-transitions 0_i ⁺→2 ⁺_f in the cases when these processes are allowed.