Exploration of resonance properties in chiral perturbation theory with   explicit U_A(1) anomaly
  We study the resonance properties within chiral perturbation theory by explicitly taking into account the U_A(1) anomaly effect. This assures we have the appropriate degrees of freedom of low energy QCD in the large Nc limit. We calculate the various resonance properties, such as mass, width and residues, for the physical case, i.e. Nc=3. Then we extrapolate the values of Nc to study the trajectories of resonance poles. 
Zhi-Hui Guo, J.A.Oller
hep-ph nucl-th