Dispersion Relations forp−nScattering

The application of dispersion relations to low-energy $p-n$ scattering is examined. It is shown that Khuri's dispersion relation can be extended to include tensor forces, but serious difficulties appear on attempting to include exchange forces. The application of the relativistic field theory dispersion relations to low-energy scattering is made by using the effective range formula. The spurious poles of the $S$-matrix are related to the two- and three-pion terms in the unphysical region contribution for forward scattering.