Supersymmetric grand unification and lepton universality in image decays Original Research Article

Motivated by the prospects for an improved test of lepton universality in image decays by the NA62 experiment at CERN, we study predictions for the possible lepton non-universality in image decays in supersymmetric models. Violations of image 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-image 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 image decays in specific regions of the parameter space with high image, large A terms and small charged Higgs boson mass. Observable non-universality in image decays would be correlated with a large value of image. 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.