Flavor-Singlet Axial Coupling Constant in the QCD Sum Rule

摘要

A QCD sum rule for the flavor-singlet axial coupling constant has been derived from two-point correlation functions of flavor singlet-octet and flavor octet-octet axial vector currents in a one-nucleon state. The evaluation of the correlation functions using operator product expansion relates singlet and octet axial coupling constants to the sigma terms and the moments of parton distributions. A good agreement with experimental results has been achieved without involving any instanton effects.