ar X iv : h ep - p h / 03 03 14 2 v 1 17 M ar 2 00 3 Nucleon - Nucleon Scattering under Spin - Isospin Reversal in Large - N c QCD

The spin-flavor structure of certain nucleon-nucleon scattering observables derived from the large Nc limit of QCD in the kinematical regime where time-dependent mean-field theory is valid is discussed. In previous work [1] this regime was taken to be where the external momentum was of order Nc which precluded the study of differential cross sections in elastic scattering. Here it is shown that the regime extends down to order N 1/2 c which includes the higher end of the elastic regime. The prediction is that in the large Nc limit, observables describable via mean-field theory are unchanged when the spin and isospin of either nucleon are both flipped. This prediction is tested for proton-proton and neutron-proton elastic scattering data and found to fail badly. We argue that this failure can be traced to a lack of a clear separation of scales between momentum of order N 1/2 c and N c when Nc is as small as three. The situation is compounded by an anomalously low particle production threshold due to approximate chiral symmetry.