Global approximants with renormalization scale invariance in pQCD

Abstract

Truncated perturbative series (TPS's) of any observable have the unphysical dependence on the choice of the renormalization scale (RScl). The diagonal Pad\'e approximants (dPA's) to any TPS of an observable possess the favorable property of being invariant in the large-${\beta_0}$ limit. This means that they are invariant under the change of the RScl $\mu^2$ when the ``running'' coupling parameter ${\alpha}_s(\mu^2)$ evolves according to the one-loop renormalization group equation. We present a method which generalizes this result -- the resulting new approximants are fully RScl-invariant in the perturbative QCD (pQCD). Further, we present some numerical examples. Both the dPA's and the new approximants are global, i.e., their structure goes beyond the usual (polynomial) TPS form and thus they could reveal some non-perturbative effects.