Decoupling Spurious Baryon States in the 1/N_c Expansion of QCD

Abstract

We identify ``spurious'' states in meson-baryon scattering, those that appear in QCD for N_c > 3 but decouple for N_c = 3. The key observation is that the relevant flavor SU(3) Clebsch-Gordan coefficients contain factors of 1 - 3/N_c. We show that this method works even if SU(3) is badly broken. We also observe that resonant scattering poles lying outside naive quark model multiplets are not necessarily large N_c artifacts, and can survive via configuration mixing at N_c = 3.