Heavy-Neutrino Chirality Enhancement Of The Decay K-L-]E-Mu In Left-Right-Symmetrical Models

We study the decay K-L --> e mu in minimal extensions of the Standard Model based on the gauge groups SU(2)(L) X U(1)(Y) and SU(2)(R) X SU(2)(L) X U(1)(B-L), in which heavy Majorana neutrinos are present. In SU(2)(L) X U(1)(Y) models with chiral neutral singlets, B(K-L --> e mu) cannot be much larger than 5 x 10-(15) without violating other low-energy constraints. In SU(2)(R) X SU(2)(L) X U(1)(B-L) models, we find that heavy-neutrino-chirality enhancements due to the presence of left-handed and right-handed currents can give rise to a branching ratio close to the present experimental limit B(K-L --> e mu) < 3.3 x 10(-11).