Paper detail

On the analytically-improved running coupling in QCD

We examine, in the `t Hooft renormalization scheme, the analytic running coupling $\barα_t(Q^2)$ in QCD, using the two-loop $β$-function with positive expansion parameters $β_0$ and $β_1$. An exact integral representation is derived for this causal coupling, which is fully expressed in terms of the imaginary part of the Lambert function $W$. This integral form manifestly accounts for the universal value of the infrared limit $\barα_t(Q^2=0)= 4 π/β_0$.