Neutrinoless double-beta decay in the nucleon-pair shell model

Nuclear matrix elements (NMEs) of neutrinoless double-beta decay (0 nu beta beta) from 0(1)(+) to 0(1)(+) of Te-130 -> Xe-1(30), Xe-134 -> Ba-134, and Xe-136 -> Ba-136 are calculated in the nucleon pair shell-model framework. It is found that the NMEs of 0 nu beta beta calculated in the surface-delta approximation (SDI) and the BCS approximation with the model space truncated into the SD-pair subspace are close to each other and smaller than those predicted by the other models. The inclusion of the G pair does not alter the results significantly. When the single-particle energies are assumed to be degenerate, the calculated results in the SD-pair shell model become close to those of the other models. It is also shown that the NMEs are sensitive to the model parameters.