On the interpretation of the electroweak precision data

Abstract

The recent precision electroweak data on Γ l , s W −2 and M W M Z are compared with the three-level and the dominant-fermion-loop as well as the full one-loop standard-model predictions. While the tree-level predictions are ruled out, the dominant-fermion-loop predictions, defined by using α(M Z 2) ≅ 1 128.9 in the tree-level formulae, as well as the full one-loop predictions are consistent with the experimental data. Deviations from the dominant-fermion-loop predictions are quantified in terms of an effective Lagrangian containing three additional parameters which have a simple meaning in terms of SU (2) symmetry violation. The effective Lagrangian yields the standard one-loop predictions for specific values of these parameters, which are determined by m t and m t .