Backward-scattering extrapolations and baryon couplings

Extrapolation of an asymptotic cross section to a baryon pole cannot uniquely determine the coupling constant. The only asymptotic quantities capable of doing this are the R and A parameters. The notorious discrepancy between extrapolation of $\frac{d\sigma \left({\pi }^{-}p\right)}{du}$ and the known Δ width is shown to be purely illusory.