KLe in SU(2)L×U(1) and SU(2)L×SU(2)R×U(1) models with large neutrino masses

The expectations for B(KLe) generated by massive neutrinos are studied in detail for the SU(2)L×U(1) and SU(2)L×SU(2)R×U(1) models. The effects of Dirac and Majorana masses for the ordinary as well as for fourth-family and SU(2)L-singlet (right-handed) neutrinos are considered, taking into account all existing laboratory and cosmological constraints on the neutrino masses and mixings, as well as plausible (i.e., not requiring extreme fine-tuning) expectations for mixing between light and heavy neutrinos. We consider general SU(2)L×SU(2)R×U(1) models, in which the right-handed quark mixing matrix UR is arbitrary, as well as the special case of manifest or pseudomanifest left-right symmetry (UR=UL or UL*), and incorporate existing limits on the mass and mixing of the WR and on UR. It is found that all plausible versions of the SU(2)L×U(1) model lead to immeasurably small branching ratios. Branching ratios as large as 2×10-13 are allowed in the SU(2)L×SU(2)R×U(1) model, but only for tiny corners of parameter space. For most parameter values (including manifest and pseudomanifest left-right symmetry) one has B(KLe)*10-15. AE