The Sum Rules for Structure Functions of Polarized $e(\mu )N$ Scattering: Theory vs. Experiment

The determination of twist-4 corrections to the structure functions of polarized $e(\mu )N$ scattering by QCD sum rules is reviewed and critically analyzed. It is found that in the case of the Bjorken sum rule the twist-4 correction is small at $Q^2>5Ge{V}^2$. However, the accuracy of the today experimental data is insufficient to reliably determine ${\alpha }_s$ from the Bjorken sum rule. For the singlet sum rule – $p+n$ – the QCD sum rule gives only the order of magnitude of twist-4 correction. At low and intermediate $Q^2$ the model is presented which realizes a smooth connection of the Gerasimov-Drell-Hearn sum rules at $Q^2=0$ with the sum rules for ${\mathrm{\Gamma }}_{p,n}(Q^2)$ at high $Q^2$. The model is in a good agreement with the experiment.