Neutrinoless double-positron decay and positron-emitting electron capture in the interacting boson model

Neutrinoless double-beta decay is of fundamental importance for determining the neutrino mass. Although double electron decay is the most promising mode, in very recent years interest in double positron decay, positron emitting electron capture, and double electron capture has been renewed. We present here results of a calculation of nuclear matrix elements for neutrinoless double-beta(+) decay and positron emitting electron capture within the framework of the microscopic interacting boson model (IBM-2) for Ni-58, Zn-64, Kr-78, Ru-96, Cd-106, Xe-124, Ba-130, and Ce-136 decay. By combining these with a calculation of phase space factors we calculate expected half-lives.