Study of the V, a structure of the charged leptonic current

Abstract

Although the charged weak interactions of leptons are conventionally described by pure V - A currents, several recent models have mechanisms which admit components of other structures. It is therefore becoming increasingly important to know the experimentally allowed amounts of V + A (as well as S, P, and T) admixture. In this paper the structure of the charged leptonic weak currents is studied in the framework of two models, the fermion-mirror fermion mixing model connected with many grand unification schemes, and the left-right symmetric SU(2) L × SU(2) R × U(1) flavor model. Both of these models allow more general V, A structure of the currents. We fit the parameters of these models to experimental data from pseudoscalar meson decay, muon decay, nuclear β-decay, and inverse muon decay. We find that substantial departure from pure V - A is allowed, the best fit values of the parameters being within one standard deviation from their V - A values. In the mixing model, different mass configurations of the mirror neutrinos are considered. The case with a heavy (> m K) electron mirror neutrino and a light (⪡ m e) muon mirror neutrino is disfavored by the fit. The lower limit of the mass of the right-handed gauge boson W R in the SU(2) L × SU(2) R × U(1) model is m(W R) >3.4 m(W L) (68.3% c.l.). The left-right symmetric model fits slightly better than the mixing model. The only data explicitly disagreeing with the V - A model is the ξ-parameter in muon decay. It would be of great importance to have this parameter remeasured.