Nature of the axial-vector mesons from their Nc behavior within the chiral unitary approachL. S. Geng, E. Oset, J. R. Peláez and L. RocaEur. Phys. J. A, 39 1 (2009) 81-87DOI: https://doi.org/10.1140/epja/i2008-10689-y