Analytic Model for the QCD Running Coupling with Universal $\barα_s(0)$ Value

Abstract

We discuss the new model expression $\barα_{an}(Q^2)$ recently obtained for the QCD running coupling with a regular ghost-free behavior in the "low $Q^2$" region. Being deduced from the standard "asymptotic-freedom" expression by imposing the $Q^2$-analyticity -- without any adjustable parameters -- it obeys nice features: (i) The universal limiting value $\barα_{an}(0)=4π/β_0 \simeq 1.4$ expressed only via group symmetry factors and independent of experimental estimates on the running coupling $\barα_s(Q^2)$ (of QCD scale parameter $Λ$). This value turns out to be stable with respect to higher order corrections; (ii) Stability of IR behavior with respect to higher-loop effects; (iii) Coherence between the experimental $\barα_{an}(M_τ^2)$ value and integral information on IR $\barα_s(Q^2)$ behavior as extracted from jet physics data.