New Vector-Scalar Contributions to Neutrinoless Double Beta Decay and Constraints on<i>R</i>-Parity Violation

Abstract

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 $(\ensuremath{\beta}{\ensuremath{\beta}}_{0\ensuremath{\nu}})$ 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 $\ensuremath{\beta}{\ensuremath{\beta}}_{0\ensuremath{\nu}}$ 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 ${\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\rightarrow}{e}^{+}$ conversion in nuclei, which are in the range accessible to ongoing experiments.