Four-loop QCD analysis of the Bjorken sum rule vs data

We study the polarized Bjorken sum rule at low momentum transfers in the range 0.22 < Q < 1.73 GeV with the four-loop N 3 LO expression for the coefficient functionCBj(αs) in the framework of the common QCD perturbation theory (PT) and the singularity-free analytic perturbation theory (APT). The analysis of the PT series for CBj(αs) gives a hint to its asymptotic nature manifesting itself in the region Q < 1 GeV. It relates to the observation that the accuracy of both the three- and four-loop PT predictions happens to be at the same 10% level. On the other hand, the usage of the two-loop APT allows one to describe the precise low energy JLab data down to Q ∼ 300 MeV and gives a possibility for reliable extraction of the higher twist (HT) corrections. At the same time, above Q ∼ 700 MeV the APT two-loop order with HT is equivalent to the four-loop PT with HT compatible to zero and is adequate to current accuracy of the data. PACS: 11.10.Hi, 11.55.Hx, 11.55.Fv, 12.38.Bx, 12.38.Cy