Pion-nucleon vertex function with one nucleon off shell

The pion-nucleon vertex function with an off-mass-shell nucleon is obtained through sideways dispersion relations with the P[SUB]11[/SUB] and S[SUB]11[/SUB] pion-nucleon phase shifts as only input. Contrary to the recent calculation of Nutt and Shakin, we find that the proper and improper vertex functions behave quite differently, indicating the importance of the nucleon propagator dressing. In particular the proper vertex function is found to have two poles in the unphysical region. NUCLEAR REACTIONS pion-nucleon vertex functions, sideways dispersion relations, nucleon self-energy corrections.