Nature of the axial-vector mesons from their Nc behavior within the   chiral unitary approach
  By describing within the chiral unitary approach the s-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone Bosons, we find that the main component of the axial vector mesons b_1(1235), h_1(1170), h_1(1380), a_1(1260), f_1(1285) and the two states associated to the K_1(1270) does not follow the QCD dependence on the number of colors for ordinary qqbar mesons. 
L. S. Geng, E. Oset, J.R. Pelaez, L.Roca