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

Abstract

We study the decay K L → 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( K L → 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( K L → eμ) < 3.3 × 10 −11.