Analytic Model for the QCD Running Coupling with Universalα¯s(0)Value

We discuss the new model expression ${\overline{\alpha }}_{\mathrm{an}}\left(Q^2\right)$ 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 has nice features: (i) The universal limiting value ${\overline{\alpha }}_{\mathrm{an}}\left(0\right)=4\mathrm{}\pi /{\beta }_0$ expressed only via group symmetry factors and independent of experimental estimates on the running coupling ${\overline{\alpha }}_s\left(Q^2\right)$ (of QCD scale parameter $\Lambda$). 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 ${\overline{\alpha }}_{\mathrm{an}}\left(M_{\tau }^2\right)$ value and integral information on IR ${\overline{\alpha }}_s\left(Q^2\right)$ behavior as extracted from jet physics data.