Strange Isosinglet Versus Octet Scalar Axial Current
  The flavor SU(3)_f group symmetry of QCD is systematically considered as the heavy c quark limit of SU(4)_f. Within that scheme we argue that the U(1)_A anomaly prevents Gell-Mann's choice for the realization of the su(4)_f (and thereby the su(3)_f) algebra for the particular case of the neutral axial currents. Rather, Weyl's choice for the SU(4)_f generators has to be used which leads to a neutral strong axial current having same structure (up to a constant factor) as the weak one. 
M. Kirchbach