No abstract

Many models for physics beyond the Standard Model predict lepton-flavour violating decays of charged leptons at a level which may become observable very soon. In the present paper we investigate the decays of a τ into three charged leptons in a generic way, based on effective-field-theory methods, where the relevant operators are classified according to their chirality structure. We work out the decay distributions and discuss phenomenological implications.

We perform a complete "Michel parameter" analysis of all possible helicity structures which can appear in the process B → X c ℓν ℓ . We take into account the full set of operators parametrizing the effective Hamiltonian and include the complete one-loop QCD corrections as well as the non-perturbative contributions. The moments of the leptonic energy as well as the combined moments of the hadronic energy and hadronic invariant mass are calculated including the non-standard contributions.

We analyse the spin structure of inclusive semileptonic b → c transitions and the effects of non-standard model couplings on the rates and the spectra. The calculation includes the O(α s ) corrections as well as the leading non-perturbative ones.