Low-energy pion-nucleon scattering

Using the divergence of the axial-vector current as the pion interpolating field and a soft-pion limit we derive a once-subtracted Low equation for the off-mass-shell $\pi N$ amplitude. The $\sigma$ commutator term and the once-subtracted $z$ graphs are the main isoscalar and isovector driving terms. The calculated $S$-wave phase shifts are in good agreement with the experimental data when we use $\left|g_{\pi }\right(4\mathrm{}{M}^2\left)\right|=11.69$ and 25.5 MeV for the $\sigma$ commutator term.