Ingredients of nuclear matrix element for two-neutrino double-beta decay   of 48Ca
  Large-scale shell model calculations including two major shells are carried out, and the ingredients of nuclear matrix element for two-neutrino double beta decay are investigated. Based on the comparison between the shell model calculations accounting only for one major shell ($pf$-shell) and those for two major shells ($sdpf$-shell), the effect due to the excitation across the two major shells is quantitatively evaluated. 
Y. Iwata, N. Shimizu, Y. Utsuno, M. Honma, T. Abe, and T. Otsuka
nucl-th nucl-ex