Duality condition for s- and t-channel exchange in nucleon-nucleon   scattering
  We specify conditions under which the nucleon-nucleon interaction, based on the t-channel meson-exchange mechanism, is equivalent to an interaction generated via an s-channel exchange of six-quark bags. The duality is possible provided the alternation of zeros and poles of the non-dispersive part of D function takes place in the normalization where the imaginary part of D is non-negative and the CDD poles are the only poles of D. 
M. I. Krivoruchenko, Amand Faessler
nucl-th