Analytic Model for the QCD Running Coupling with Universal α̅ _s(0) Value

We discuss the new model expression α̅ _an(Q²) recently obtained for the QCD running coupling with a regular ghost-free behavior in the “low Q²” region. Being deduced from the standard “asymptotic-freedom” expression by imposing the Q² analyticity—without any adjustable parameters—it has nice features: (i) The universal limiting value α̅ _an(0) = 4π/β₀ expressed only via group symmetry factors and independent of experimental estimates on the running coupling α̅ _s(Q²) (of QCD scale parameter Λ). This value is stable with respect to higher order corrections. (ii) Stability of IR behavior with respect to higher-loop effects. (iii) Coherence between the experimental α̅ _an(M_τ²) value and integral information on IR α̅ _s(Q²) behavior as extracted from jet physics data.