Baryon and Lepton Number Violation with Scalar Bilinears
  We consider all possible scalar bilinears, which couple to two fermions of the standard model. The various baryon and lepton number violating couplings allowed by these exotic scalars are studied. We then discuss which ones are constrained by limits on proton decay (to a lepton and a meson as well as to three leptons), neutron-antineutron oscillations, and neutrinoless double beta decay. 
H.V. Klapdor-Kleingrothaus, E. Ma and U. Sarkar