The effect of weak magnetism and induced pseudoscalar coupling in neutrinoless double-beta decay

In calculating the amplitude of the Majorana neutrino-mass mechanism of neutrinoless double-beta decay (0νββ-decay), several approximations of the nucleon current have been done. For example, effects from induced current such as weak magnetism and pseudoscalar coupling have been neglected. We shall show in this work that, although such terms do not contribute significantly to the 2νββ-decay amplitude, they are important in the case of 0νββ decay. Performing calculations within the renormalized quasiparticle random phase approximation (pn-RQRPA) for all nuclei undergoing double-beta decay in the region A = 76 to A = 150, we have found that these additional contributions of the nucleon current reduce considerably the matrix elements in all cases for the light neutrino as well as for the heavy neutrino mass. In the light-neutrino mass, we find reductions up to thirty percent, while in the heavy-neutrino mass, up to almost a factor of five. These reductions make the limits on the lepton-number-violating parameters and ηN less stringent