pi N --> Multi-pi N Scattering in the 1/N_c Expansion
  We extend the 1/N_c expansion meson-baryon scattering formalism to cases in which the final state contains more than two particles. We first show that the leading-order large N_c processes proceed through resonant intermediate states (e.g., rho N or pi Delta). We then tabulate linear amplitude expressions for relevant processes and find that the pole structure of baryon resonances can be uniquely identified by their (non)appearance in eta N or mixed partial-wave pi Delta final states. We also show that quantitative predictions of pi N to pi Delta branching ratios predicted at leading order alone do not agree with measurements, but the inclusion of 1/N_c corrections is ample to explain the discrepancies. 
Herry J. Kwee, Richard F. Lebed