Glue and Charm in Light Quark Physics

The main input of our approach is the information on the instanton structure of the QCD vacuum and on the quark propagation in such an instanton background.To our present knowledge, the packing parameter of the instantons is small, legitimating independent averaging over positions and orientations of the instantons.In the present work it is rederived the Effective Action of Diakonov and Petrov (DP) starting from results of Lee and Bardeen.We apply this Effective Action to the calculations of the matrix elements of a gluon operators including also that ones generated by virtual charm quarks.In quasiclassical (saddle point) approximation any gluon operator derives its main contribution from instanton background.First, we check this approach by the low-energy theorems(LET) generated by QCD+QED axial anomaly which are constitute sensitive tests for any quark models.We found that the single-instanton approximation and its modifications badly violate LET.On the contrary the DP model, which takes into account the multiinstanton effects in the propagation of the quarks, agrees satisfactory with this theorem in the chiral limit. However, beyond such a limit, even this model violates LET.So, in the chiral limit we find that DP model satisfy LET, however, beyond such a limit, even this model violates LET. This conclusion provided solid background for the calculations of the matrix elements of gluon operators in the chiral limit.

Further we focus on the calculation in the chiral limit of f_{\eta'}^{(c)}, the amplitude of the (c\bar{c}) \to (gluons) \to \eta^{'} transition, which provides the magnitude of the contribution of the Cabbibo favored b → \bar c c s elementary process to B \to \eta ' K decay. It is found that f_{\eta '}^{(c)} = - 12.3 ～ -18.4 MeV on the scale of m_{c}. The same approach leads to the estimations of the Charm contribution to the spin content of nucleon as Δc/Σ = -0.03.