Electroweak Theory and the 1996/97 Precision Electroweak Data

We review the empirical evidence for the validity of the Standard Electroweak Theory in Nature. The experimental data are interpreted in terms of an effective Lagrangian for Z physics, allowing for potential sources of SU(2) violation and containing the predictions of the Standard Electroweak Theory as a special case. Particular emphasis is put on discriminating loop corrections due to fermion-loop vector-boson propagator corrections on the one hand, from corrections depending on the non-Abelian structure and the Higgs sector on the other hand. Results from recently obtained fits of the Higgs-boson mass are reported, yielding M_H < 430 GeV [680 GeV] at 95% C.L. based on the input of \swbar^2(\LEP+\SLD)_{97} = 0.23152 +- 0.00023 [\swbar^2(\LEP)_{97} = 0.23196 ± 0.00028]. The LEP2 data provide first direct experimental evidence for non-zero non-Abelian couplings among the electroweak vector bosons.