Unpolarized and spin-dependent DIS structure functions in Double-Logarithmic Approximation

Abstract

We demonstrate how to calculate perturbative components of the structure functions F1 (for unpolarized DIS) and gi (spin-dependent DIS) in Double-Logarithmic Approximation, studying separately the cases of fixed and running QCD coupling. We show that as long as only ladder graphs are accounted for (throughout the talk we use the Feynman gauge for virtual gluons) there is no difference at all between F1 and g1. However, accounting for contributions of non-ladder graphs brings an essential difference between them. Applying Saddle-Point method to expressions for F1 and g1, we obtain their small-x asymptotics. The both asymptotics are of the Regge kind but with different intercepts. The intercept of F1 proved to be greater than unity, so it is a new contribution to Pomeron. We show the reason for the g1 intercept should be less than the one of F1 and thereby argue against using model Pomerons in the spin-dependent processes. Finally, we discuss the applicability region of Regge asymptotics.