Virtualities of quarks and gluons in a QCD vacuum and nonlocal condensates within the 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 ${\ensuremath{\lambda}}_{q}^{2}\ensuremath{\equiv}〈:\overline{q}{D}^{2}q:〉/〈:\overline{q}q:〉$ and gluons ${\ensuremath{\lambda}}_{g}^{2}\ensuremath{\equiv}〈:G{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{D}}^{2}G:〉/〈:GG:〉$ in the QCD vacuum and obtain parameterless predictions for the ratio ${\ensuremath{\lambda}}_{g}^{2}/{\ensuremath{\lambda}}_{q}^{2}=12/5,$ and for some ratios of different vacuum condensates of higher dimensions. The nonlocal properties of quark and gluon condensates are analyzed, and the insufficiency of the single instanton approximation is discussed.

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