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 β. Based on the AGK rules, we comment on the possible contribution from diffractive higher twists to ∝ 1 Q 2 corrections to proton structure function at small x. These corrections to the longitudinal structure function F L may be particularly large.

We propose a new method of the determination of R D = σ

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We calculate the diffraction slope B D for diffractive DIS. We find a coun-

We derive a unitarity relationship between the spin structure function g LT (x, Q 2 ) = g 1 (x, Q 2 )+ g 2 (x, Q 2 ), the LT interference diffractive structure function and the spin-flip coupling of the pomeron to nucleons. Our diffractive mechanism gives rise to a dramatic small-x risewhere δ g is an exponent of small-x rise of the unpolarized gluon density in the proton g(x, Q 2 ) at a moderate hard scale Q 2 for light flavour contribution and large hard scale Q 2 ∼ m 2 f for heavy flavour contribution. It invalidates the Burkhardt-Cottingham sum rule. The found small-x rise of diffraction driven g LT (x, Q 2 ) is steeper than given by the Wandzura-Wilczek relation under conventional assumptions on small-x behaviour of g 1 (x, Q 2 ).