  We present a new gauge-independent approach to resonant transition amplitudes
with nonconserved external currents, based on the pinch technique method. In
the context of $2\to 2$ and $2\to 3$ 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 well as bosonic contributions to the
resummed gauge boson propagators, does not contain any residual space-like
threshold terms, shows the correct high-energy unitarity behaviour, admits
renormalization, and satisfies a number of other required properties, including
the optical theorem. 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
renormalizable models of new physics.
