content_image/352516.jpg
<img src='content_image/352516.jpg'>

comparison are, on the left panel, the results in the g$_{1}$ scheme: α$_{g}$$_{1}$ ( r ) from JLab data (lower cross-hatched band), the light-front holographic result from Eqs. 11 and 18 (continuous line) and lattice results from [38] (upper cross-hatched band). The same scales are used on both panels. The fact that different schemes imply different values for the IR fixed point of α$_{s}$ is exemplified in this figure in which α$_{s}$ ( r ) in the V scheme and in the g$_{1}$ scheme freeze to the IR fixed point values of α$_{V}$ ( Q = 0) = 2 . 2 and α$_{g}$$_{1}$ ( Q = 0) = π respectively. 

The width of the lower band on the right hand panel is the combined uncertainty on α$_{V}$ coming from: a) the uncertainty in the value Λ$_{QCD}$, b) the truncation of the pQCD β -series used to calculate α$_{MS}$ in the perturbative region, c) the truncation of the pQCD CSR at Q ∗∗∗ which, has been estimated by using the difference between the Q ∗∗ and Q ∗∗∗ orders and d) the experimental uncertainties on the JLab data for α$_{g}$$_{1}$ . The uncertainty coming from the truncation of the pQCD series for the Bjorken sum rule is negligible. 

The experimental results for α$_{g}$$_{1}$ ( r ) follow from the integrated JLab data according to Eq. (17). The contributions to the integral from the unmeasured low Q ( Q < 0 . 23 GeV) and high Q ( Q > 1 . 71 GeV) regions are computed using the sum rules [40] and [12] respectively. The total experimental uncertainties, as well as the uncertainty on the large Q region, are 

