Nc limit of spin-flavor breaking in excited baryon levels

Spin-flavor symmetry breaking in the levels of excited baryons are studied to leading order in the 1Nc expansion. This breaking occurs at zeroth order. For non-strange baryons with a single quark excited, it is shown that to first order of perturbation theory the breaking is given by one 1-body operator (spin-orbit), and three 2-body operators, all involving the orbital angular momentum of the excited quark. Higher-body operators can be reduced to that set of operators. As illustration, p-wave baryons are briefly discussed.