Supersymmetric Grand Unification and Lepton Universality in K-> l \nu Decays

TL;DR

This paper explores how supersymmetric models could lead to observable violations of lepton universality in K -> l nu decays, especially in non-minimal grand unified theories with high tan beta, providing a potential test for supersymmetric flavor physics.

Contribution

It predicts possible lepton non-universality in K decays within supersymmetric models, highlighting the role of right-handed slepton mixing and non-minimal GUT scenarios with high tan beta.

Findings

Lepton non-universality may be observable in specific SUSY parameter regions.

Such violations are correlated with large BR(τ → e γ).

Constraints on model parameters can be derived even if no violation is observed.

Abstract

Motivated by the prospects for an improved test of lepton universality in K -> l \nu decays by the NA62 experiment at CERN, we study predictions for the possible lepton non-universality in K -> l \nu decays in supersymmetric models. Violations of \mu-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-\tan\beta 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 higher-dimensional 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 -> l \nu decays in specific regions of the parameter space with high \tan \beta, large A terms and small charged Higgs boson mass. Observable non-universality in K -> l \nu decays would be correlated with a large value of BR(\tau -> e \gamma). 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.