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-ene rgy constraints. In SU(2)(R) X SU(2)(L) X U(1)(B-L) models, we find th at heavy-neutrino-chirality enhancements due to the presence of left-h anded and right-handed currents can give rise to a branching ratio clo se to the present experimental limit B(K-L --> e mu) < 3.3 x 10(-11).