NEW VECTOR-SCALAR CONTRIBUTIONS TO NEUTRINOLESS DOUBLE-BETA DECAY AND CONSTRAINTS ON R-PARITY VIOLATION

We show that in the minimal supersymmetric standard model (MSSM), with R-parity breaking as well as in the left-right symmetric model, there are new observable contributions to neutrinoless double beta decay (beta beta(0 nu)) arising from hitherto overlooked diagrams involving the exchange of one W boson and one scalar boson. In particular, in the case of MSSM, the present experimental bounds on beta beta(0 nu) lifetime improves the limits on certain R-parity violating couplings by about 2 orders of magnitude. It is shown that similar diagrams also lead to enhanced rates for mu(-) --> e(+) conversion in nuclei, which are in the range accessible to ongoing experiments.