IHEP 98 - 50
	Yu.F. Pirogov O.V. Zenin
	Two-loop Renormalization Group Restrictions on the Standard Model and the Fourth Chiral Family
	Protvino, 1998.- p.21, figs. 11, refs.:27.

Nonperturbative studies of strong running coupling constant in the infrared region are discussed. Starting from the analyses of the Dyson-Schwinger equations in the gauge sector of QCD, the conclusion is made on an incomplete fixing of the perturbation theory summation ambiguity within "(forced) analytization procedure" (called also a dispersive approach). The minimal model for anti-alpha_s (q2) is proposed so that the perturbative time-like discontinuity is preserved and nonperturbative terms not only remove the Landau singularity but also provide the ultraviolet convergence of the gluon condensate. Within this model, on the one hand, the gluon zero modes are enhanced (the dual superconductor property of the QCD vacuum) and, on the other hand, the dynamical gluon mass generation is realized with m_g estimated as 0.6 GeV. The uncertainty connected with the division into perturbative and nonperturbative contributions is discussed with gluon condensate taken as an example.

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