GAUGE-INDEPENDENT APPROACH TO RESONANT TRANSITION AMPLITUDES

We present a new gauge-independent approach to resonant transition amp litudes with nonconserved external currents, based on the pinch techni que method. In the context of 2 --> 2 and 2 --> 3 scattering processes we show explicitly that the analytic results derived respect U(1)(em) gauge symmetry and do not depend on the choice of the SU(2)(L) gauge fixing. Our analytic approach treats, on equal footing, fermionic as w ell as bosonic contributions to the resummed gauge boson propagators, does not contain any residual spacelike threshold terms, shows the cor rect high-energy unitarity behavior, admits renormalization, and satis fies a number of other required properties, including the optical theo rem. Even though our analysis has mainly focused on the standard model gauge bosons, our method can easily be extended to the top quark, and be directly applied to the study of unstable particles present in ren ormalizable models of new physics.