Origin of the Q²-dependence of the DIS structure functions

We consider in detail Q²-dependence of the DIS structure functions. Very often this dependence is claimed to be originated by the Q²-dependence of the QCD coupling. This leads to the small-x asymptotics of the structure functions with Q²-dependent intercepts. We demonstrate that the DGLAP parametrization α_s = α_s(Q²) is an approximation valid in the region of large x (where 2pq can be approximated by Q²) only, providing the factorization scale is also large. Outside this region, the DGLAP parametrization fails, so α_s should be replaced by an effective coupling which is independent of Q² at small x. As a consequence, intercepts of the structure functions are independent of Q². Nevertheless, the small-x asymptotics of the structure functions explicitly depend on Q², even when the coupling does not depend on it. We also consider the structure functions at small Q² and give a comment on power-Q² corrections to the structure functions at large and small Q².