STABLE CALCULATIONS FOR UNSTABLE PARTICLES - RESTORING GAUGE-INVARIANCE

We discuss theoretical and phenomenological aspects of the use of boso n propagators with energy-dependent widths in predictions for high-ene rgy scattering processes, In general, gauge invariance is violated in such calculations. We discuss several approaches to restore gauge inva riance, necessary for a reliable result. The most promising method is the addition of the relevant parts of the fermionic corrections, which fulfills all Ward identities, The numerical difference between this a nd other approaches is studied. A number of recommendations are given for LEP2 computations.