GAUGE-INVARIANT FORMULATION OF THE S, T, AND U PARAMETERS

It is shown that the bosonic contributions to the S, T, and U paramete rs, defined in terms of conventional self-energies, are gauge dependen t in the standard model (SM). Moreover, T and U are divergent unless a constraint is imposed among the gauge parameters. Implications of thi s result for renormalization schemes of the SM are discussed. A gauge- invariant formulation of S, T, and U is proposed in the pinch-techniqu e framework. The modified S, T, and U parameters provide a gauge-invar iant parametrization of leading electroweak radiative corrections in t he SM and some of its extensions.