GAUGE-INVARIANCE, ANALYTICITY AND PHYSICAL OBSERVABLES AT THE Z0 RESONANCE

Most calculations of the electroweak radiative corrections to e+e- annihilation near the Z0 resonance contain spurious higher-order gauge-dependent contributions. It is shown how to develop, to arbitrary accuracy, a perturbative expansion that is exactly gauge invariant at each order and produces expressions that are particularly simple in form. Experiments at LEP currently extract the value of the renormalized mass in the on-shell scheme for the physical Z0 mass. It is shown that this definition differs from the traditional one based on the position of the pole of the scattering amplitude by 35 MeV or more than 1-sigma of the present experimental accuracy. The gauge-invariant expansion proposed here makes the latter definition the natural choice.