Axial anomaly and instanton vacuum models in QCD

The test of instanton models of quantum chromodynamics(QCD), in particular the single instanton approximation and the Diakonov and Petrov (DP) model against some exact relations inferred from QCD + QED axial anomaly is discussed. It is shown that single-instanton approximation and its modifications badly violate low-energy theorem(LET). On the contrary the DP model, which takes into account the multiinstantion effects in propagation of quarks agrees satisfactory with this theorem in the chiral limit. However, beyond such a limit even this model violates LET