Heavy-neutrino chirality enhancement of the decay KL → eμ in left-right symmetric models

We study the decay KL → eμ in minimal extensions of the Standard Model based on the gauge groups SU(2)L ⊗ U(1)γ and SU(2)R ⊗ SU(2)L ⊗ U(1)B-L, in which heavy Majorana neutrinos are present. In SU(2)L ⊗ U(1)γ models with chiral neutral singlets, B(KL → eμ) cannot be much larger than 5 × 10−15 without violating other low-energy constraints. In SU(2)R ⊗ SU(2)L ⊗ 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(KL → eμ) < 3.3 × 10−11.