Bjorken Sum Rule and pQCD frontier on the move

Understand

The reasonableness of the use of perturbative QCD notions in the region close to the scale of hadronization, i.e., below $\lesssim 1 \GeV$ is under study.

• First, the interplay between higher orders of pQCD expansion and higher twist contributions in the analysis of recent Jefferson Lab (JLab) data on the Generalized Bjorken Sum Rule function $\Gamma_1^{p-n} (Q^2)$ at $0.1<Q^2< 3 {\rm GeV}^2$ is studied.
• It is shown that the inclusion of the higher-order pQCD corrections could be absorbed, with good numerical accuracy, by change of the normalization of the higher-twist terms.
• Second, to avoid the issue of unphysical singularity (Landau pole at $Q=\Lambda\sim 400 \MeV $), we deal with the ghost-free Analytic Perturbation Theory (APT) that recently proved to be an intriguing candidate for a quantitative description of light quarkonia spectra within the Bethe-Salpeter approach.