  We use contracted spin-flavor symmetry which emerges in the large Nc limit of
QCD to obtain relations between proton-proton and proton-neutron total cross
sections for both polarized and unpolarized scattering. The formalism used is
valid in the semi-classical regime in which the relative momentum of the
incident nucleons is much larger than the inverse size of the nucleon, provided
that certain technical assumptions are met. The relations should be
phenomenologically useful provided that Nc=3 is sufficiently large so that the
large Nc results have at least semi-quantitative predictive power. The
relations are model-independent in the sense that they depend on properties of
large Nc QCD only and not on any particular model-dependent details of the
nucleon-nucleon interaction. We compare these model-independent results to
experimental data. We find the relation for spin-unpolarized scattering works
well empirically. For the case of polarized scattering, the data is consistent
with the relations but the cross sections are too small to make sharp
predictions.
