On the Analytic “Causal” Model for the QCD Running Coupling

We discuss the model ᾱan(Q ) recently proposed for the QCD running coupling ᾱs(Q ) in the Euclidean domain on the basis of the “asymptotic–freedom” expression and on causality condition in the form of the Q-analyticity. The model contains no adjustable parameters and obeys the important features: (i) Finite ghost-free behavior in the “low Q” region and correspondence with the standard RG-summed UV expressions;(ii) The universal limiting value ᾱan(0) expressed only via group symmetry factors. This value as well as the ᾱan behavior in the whole IR region Q ≤ Λ turns out to be stable with respect to higher loop corrections; (iii) Coherence between observed ᾱs(M 2 τ ) value and integral information on the IR ᾱs(Q ) behavior extracted from jet physics.