Gauge-independent analysis of KL → eμ in left-right models Original Research Article

The lepton-flavour-violating decay KL → eμ is studied in detail within the context of SU(2)R ⊗SU(2)L ⊗U(1)(B−L) models, which include heavy Majorana neutrinos. Particular attention is paid to the gauge independence of this decay process to one loop. In analogy with earlier studies on the K0K0 mixing, it is explicitly shown how restoration of gauge invariance occurs in the decay amplitude containing the box diagrams, when the relevant Higgs-dependent self-energy and vertex graphs are taken into account in the on-shell skeleton renormalization scheme. Based on the analytic expressions so derived, we find that the branching ratio B(KL → eμ) can be considerably enhanced due to the presence of left- and right-handed currents in the loop, and can reach values close to or even larger than the present experimental limit 3.3 × 10−11 in the manifest left-right symmetric model. Constraints on the parameter space of typical left-right models are derived from the possible decay KL → eμ and a global analysis of other low-energy data.