Analyticity and Minimality of Nonperturbative Contributions in Perturbative region for $\bar\alpha_s$

Abstract

It is shown, that the possibility of a freezing of QCD running coupling constant at zero in the approach with "forced analyticity" can not be in accord with Schwinger-Dyson equation for gluon propagator. We propose to add to the analytic expression the well-known infrared singular term $1/q^2$ as well as pole term corresponding to "excited gluon". With this example we formulate the principle of minimality of nonperturbative contributions in perturbative (ultraviolet) region, which allows us to fix ambiguities in introduction of nonperturbative terms and maintain the finiteness of the gluon condensate. As a result we obtain estimates of the gluon condensate, which quite agree with existing data. The nonzero effective mass of the "excited gluon" leads also to some interesting qualitative consequences.