Analytic Model for the QCD Running Coupling with Universal ${\bar{\alpha }}_s(0)$ Value

We discuss the new model expression ${\bar{\alpha }}_{an}(Q^2)$ 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 ${\bar{\alpha }}_{an}(0)=4\pi \mathrm{/}{\beta }_0\simeq 1.4$ expressed only via group symmetry factors and independent of experimental estimates on the running coupling ${\bar{\alpha }}_s(Q^2)$ (of QCD scale parameter $\mathrm{\Lambda }$). 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 ${\bar{\alpha }}_{an}(M_{\tau }^2)$ value and integral information on IR ${\bar{\alpha }}_s(Q^2)$ behavior as extracted from jet physics data.