Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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Motivated by the data from Super-Kamiokande and elsewhere indicating oscillations of atmospheric and solar neutrinos, we study charged-lepton-flavour violation, in particular the radiative decays µ → eγ and τ → µγ, but also commenting on µ → 3e and τ → 3µ/e decays, as well as µ → e conversion on nuclei. We first show how the renormalization group may be used to calculate flavour-violating soft supersymmetrybreaking masses for charged sleptons and sneutrinos in models with universal input parameters. Subsequently, we classify possible patterns of lepton-flavour violation in the context of phenomenological neutrino mass textures that accommodate the SuperKamiokande data, giving examples based on Abelian flavour symmetries. Then we calculate in these examples rates for µ → eγ and τ → µγ, which may be close to the present experimental upper limits, and show how they may distinguish between the different generic mixing patterns. The rates are promisingly large when the soft supersymmetry-breaking mass parameters are chosen to be consistent with the cosmological relic-density constraints. In addition, we discuss µ → e conversion on Titanium, which may also be accessible to future experiments.

We propose a simple parametrization for the deep-inelastic diffractive cross section. It contains the contribution of qq production to both the longitudinal and the transverse diffractive structure functions, and of the production of qqg final states from transverse photons. We start from the hard region and perform a suitable extrapolation into the soft region. We test our model on the 1994 ZEUS and H1 data, and confront it with the H1 conjecture of a singular gluon distribution.