J. Papavassiliou et A. Pilaftsis, GAUGE-INDEPENDENT APPROACH TO RESONANT TRANSITION AMPLITUDES, Physical review. D. Particles and fields, 53(4), 1996, pp. 2128-2149
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.