Many-body correlations of QRPA in nuclear matrix elements of double-beta decay

We present two new ideas on the quasiparticle random-phase approximation (QRPA) approach for calculating nuclear matrix elements of double-beta decay. First, it is necessary to calculate overlaps of the QRPA states obtained on the basis of the ground states of different nuclei. We calculate this overlap using quasiboson vacua as the QRPA ground states. Second, we show that two-particle transfer paths are possible to use for the calculation under the closure approximation. A calculation is shown for ¹⁵⁰Nd→¹⁵⁰Sm using these two new ideas, and their implication is discussed