Abstract
Starting with assumptions about current and field commutators we derive Ward identities for 3 point functions of nucleon and meson. For 4 point functions we derive reduced Ward identities for the nonpole part of the amplitude. Combined with assumptions that vertex functions and nonpole parts of the amplitude are slowly varying in all 4-momenta, we rederive the same results as particle dominance in dispersion theory for vector and axial vector form factors, and we obtain predictions for the 8 low energy πN scattering parameters in terms of 4 unknown parameters. The fit is in reasonable agreement with experiment and somewhat improved by considering explicitly N ∗ contributions. Our calculations show it is a good approximation to take the strong pion-nucleon coupling, gF s ( K 2) as a constant. We do not set the pion mass equal to zero.
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