Pion Exchange Currents in Neutrinoless Double Beta Decay and Limits on Supersymmetry

We examine the pion exchange mode of neutrinoless double beta decay induced by the R-parity violating quark-lepton operators of the supersymmetric (SUSY) extensions of the standard model of the electroweak interactions. The corresponding nuclear matrix elements are evaluated within the renormalized quasiparticle random phase approximation with proton-neutron pairing, which includes the Pauli effect of fermion pairs and does not collapse for a physical value of the nuclear force strength. It is argued that the pion-exchange mode of neutrinoless double beta decay dominates over the conventional two-nucleon mode in the case of the SUSY mechanism. As a result sensitivity of neutrinoless double beta decay to the SUSY contribution turns out to be significantly better that previously expected from the two-nucleon mode calculations. An upper limit on the R-parity violating coupling $\lambda'_{111}$ is derived from non-observation of neutrinoless double beta decay. This limit is much stronger than that expected from the near future accelerator experiments.