The Lorentz structure of leptonic charged weak interactions

We analyze all available data on leptonic, charge changing, weak interactions in terms of more general Lorentz structures than V - A. For this purpose we construct classes of models which follow the pattern of unified gauge theories but which are general enough so as to make use of the nearly complete experimental information. In a first class of models we assume the interactions to be mediated by the exchange of charged bosons whose couplings to leptons fulfill either strict universality or modified universality (for spin-zero exchanges). In a second class of models we investigate to which extent the data admit or require unconventional couplings in addition to V - A. A chi2 analysis is presented for nine typical cases and limits on non-canonical couplings are given. As expected the data admit relatively large deviations from V - A. A few per mill measurement of the parameter xi in μ decay as well as an absolute measurement of the muon neutrino helicity from pion decay would help to remedy this unsatisfactory situation. (orig.)