Running coupling at low momenta, renormalization schemes, and renormalons

We propose a method for summing a perturbation-theory asymptotic series tha t is related to infrared (IR) renormalons in QCD using special renormalizat ion schemes in which the running coupling constant can be integrated over t he small momenta. For our method to work, we should consider higher order p erturbation-theory corrections to the standard bubble-chain diagrams. High- order corrections allow one to choose a scheme in which the coupling-consta nt evolution Carl be smoothly extrapolated to low momenta. In these schemes , the surd of all (extended) IR-renormalon asymptotic series is defined as all integral of the running coupling constant over the IR region. We presen t explicit examples of renormalization schemes of QCD that call be used to sure IR-renormalon asymptotic series according to our definition. (C) 2001 MAIK "Nauka/Interperiodica".