Virtualities of Quarks and Gluons in QCD Vacuum and Nonlocal Condensates within Single Instanton Approximation

We calculate the lowest-dimensional nonlocal quark and gluon condensates within the single instanton approximation of the instanton liquid model. As a result, we determine the values of average virtualities of quarks $\lambda_q^2$ and gluons $\lambda_g^2$ in the QCD vacuum and obtain parameterless predictions for the ratio $\lambda_g^2/\lambda_q^2 = 12/5$, and for some ratios of different vacuum condensates of higher dimensions. The nonlocal properties of quark and gluon condensates are analyzed, and insufficiency of the single instanton approximation is discussed.