Dispersive approach to the axial anomaly and nonrenormalization theorem
  Anomalous triangle graphs for the divergence of the axial-vector current are studied using the dispersive approach generalized for the case of higher orders of perturbation theory. The validity of this procedure is proved up to two-loop level. By direct calculation in the framework of dispersive approach we have obtained that the two-loop AVV amplitude is equal to zero. According to the Vainshtein's theorem the transversal part of the anomalous triangle is not renormalized in the chiral limit. We generalize this theorem for tha case of finite fermion mass in the triangle loop. 
R. S. Pasechnik, O. V. Teryaev