Under assumption of singular behavior of invariant charge αs(q2) at q2≃0 and of large q2 behavior, corresponding to the perturbation theory up to four loops, a procedure is considered of smooth matching the β-function at a boundary of perturbative and nonperturbative regions. The procedure results in a model for αs for all q2>0 with dimensionless parameters being fixed and dimensional parameters being expressed in terms of only one quantity Λ QCD . The gluon condensate which is defined by the nonperturbative part of the invariant charge is calculated for two variants of "true perturbative" invariant charge, corresponding to freezing option and to analytic one in nonperturbative region. Dimensional parameters are fixed by varying normalization condition [Formula: see text]. It is obtained that on the boundary of perturbative region [Formula: see text], the procedure results in nonperturbative Coulomb component α Coulomb ≃0.25, the nonperturbative region scale q0≃1 GeV , the model parameter σ≃(0.42 GeV )2 which suits as string tension parameter, the gluon condensate appears to be close for two variants considered, K≃(0.33–0.36 GeV )4 (for [Formula: see text]).
A MANIFESTLY GAUGE INVARIANT AND UNIVERSAL CALCULUS FORSU(N) YANG–MILLS
