Twist-4 effects and $Q^2$ dependence of diffractive DIS

Abstract

In this letter we report the direct perturbative QCD evaluation of twist-4 effects in diffractive DIS. They are large and have a strong impact on the $Q^2$ dependence of diffractive structure functions at large $\beta$. Based on the AGK rules, we comment on the possible contribution from diffractive higher twists to $\propto \frac{1}{Q^2}$ corrections to proton structure function at small $x$. These corrections to the longitudinal structure function $F_L$ may be particularly large.

13 pages LaTeX including 4 PS figures