Contributions of Spin-J Baryon Poles to πN → πN and πN → γN Amplitudes

Contributions of baryon poles of spin J to the πN → πN and πN → γN amplitudes have been calculated using the Wigner‐Bargmann formalism. An ambiguity arising from off‐the‐mass‐shell continuation of the propagator has been discussed and a continuation which gives pure spin‐J behavior of the propagator for timelike propagator momentum has been given. Moreover, it has been shown that the parts of the amplitudes (with timelike propagator momentum) containing the highest power of the cosine of the scattering angle are free of this ambiguity.