Eta-eta' masses and mixing: a large N_c reappraisal
  We reconcile the 1/N_c expansion with the observed eta-eta' mass spectrum. The chiral corrections introduced for that purpose are natural and consistent with the octet-singlet mixing angle theta=-(22\pm 1)^{\circ} extracted from phenomenology in the large N_c limit. 
J.-M. Gerard and E. Kou