The problem of two channels NN and NN*, coupled through unitarity, is studied to see whether sizable peaks can be produced in elastic nucleon-nucleon scattering due to the opening of a strongly coupled inelastic channel.One-pion-exchange (OPE) interactions are calculated to estimate the NN*→NN* and NN→NN* amplitudes.The OPE production amplitudes are used as the sole dynamical input to drive the multichannel ND-1 equations in the determinental approximation, and the effect on the J = 2+ (1D2) elastic NN scattering amplitude is studied as the width of the unstable N* and strength of coupling to the inelastic channel are varied.A cusp-type enhancement appears in the NN channel near the NN* threshold but for the known value of the N* width the cusp is so “wooly” that any resulting elastic peak is likely to be too broad and diminished in height to be experimentally prominent.A brief survey of current experimental knowledge of the real part of the 1D2 NN phase shift near the NN* threshold is given, and the values are found to be much smaller than the nearly “resonant” phase shifts predicted by the coupled channel model.
