Nuclear Physics of Non-Standard 0νββ-Decay

The observation neutrinoless double beta (0 nu beta beta) decay remains crucial for understanding lepton number violation. In view of the difficulties to observe the mass mechanism of 0 nu beta beta-decay, investigations of other mechanisms are in order. These nonstandard mechanisms can be divided into short-range and long-range mechanisms. Recently, we have started systematic study for all possible short-range and long-range non-standard mechanisms. The aim of this study is twofold: I) to provide explicit formulas for the nuclear matrix elements (NMEs) and phase-space factors (PSFs) from which the decay rate for one or a combination of mechanisms operating at the same time can be calculated; II) to provide numerical values of the NMEs and PSFs obtained by making use of the microscopic interacting boson model (IBM-2) for the NMEs and of exact Dirac wave functions for the PSFs.