Dynamical theory for the P-wave pion-nucleon interaction

We present a dynamical theory of low energy P-wave πN interaction. The theory is an extension of the Chew-Low theory, with three additional features, namely, (1) inclusion of the full nucleon recoil effect, (2) inclusion of the Z graphs, and (3) inclusion of P11 channel inelasticity. The second feature is new in a P-wave theory based on the Low expansion. We are able to fit the P33 and the P11 phase shifts in the energy region 0<T/sub π/<250 MeV quite well. In particular, we show that it is possible to explain the change of sign of the P11 phase shift, T/sub π/approx.150 MeV, in terms of the strong inelasticity present in the channel. For the P13 and P31 channels, where the phase shifts are the smallest, we do reasonably well at threshold, but not so well as the energy increases. We have also examined the structure of the off-mass-shell amplitudes in the P11 and P33 channels. Only the P33 channel amplitude is found to be factorable. A major result of our work is that the P33 form factor is very hard. If one uses a monopole form, the form-factor mass should be 10 m/sub π/ or larger