A TEST OF THE INSTANTON VACUUM CHIRAL QUARK-MODEL WITH AXIAL ANOMALY LOW-ENERGY THEOREMS

The QCD+QED axial anomaly low-energy theorems are applied to estimate the accuracy of an instanton vacuum - based chiral quark model. The lo w-energy theorems give an exact relation between the matrix elements o f the gluon and photon parts of the QCD+QED axial anomaly operator equ ation. The matrix elements between vacuum and two photon states and be tween vacuum and two gluon states are calculated for arbitrary N-f. It is shown that this model does satisfy the low-energy theorems with an accuracy of similar to 17%. We estimate also the contribution of the nonperturbative conversion of gluons into photons to the decay eta --> 2 gamma and compare with experimental data. (C) 1997 Published by Els evier Science B.V.