Supersymmetric Grand Unification and Lepton Universality in K → l ν Decays

Motivated by the prospects for an improved test of lepton universality in K → lν decays by the NA62 experiment at CERN, we study predictions for the possible lepton nonuniversality in K → lν decays in supersymmetric models. Violations of μ− e universality in this process may originate from mixing effects in the right-handed slepton sector, providing a unique window into this aspect of supersymmetric flavour physics in the large-tanβ region. Minimal unification scenarios with universal soft supersymmetry-breaking terms at the GUT scale would predict negligible violation of lepton universality. However, lepton non-universality may be observable in non-minimal grand unified models with higherdimensional terms contributing to fermion masses, in which case renormalization effects above the GUT scale may enhance the mixing among the right-handed sleptons. This could leads to observable lepton non-universality in K → lν decays in specific regions of the parameter space with high tanβ, large A terms and small charged Higgs boson mass. Observable non-universality in K → lν decays would be correlated with a large value of BR(τ → eγ). The experimental upper limit on the electric dipole moment of the electron could be reconciled with leptogenesis, if the latter occurs at a relatively low scale, which would also alleviate the cosmological gravitino problem. Even if lepton non-universality is not seen in the near future, one may nevertheless obtain significant constraints on the model parameters and unknown aspects of right-handed fermion and sfermion mixing. CERN-PH-TH/2008-140 September 2008