Diffraction driven steep rise of spin structure function g LT = g 1 + g 2 at small x and DIS sum rules

We derive a unitarity relationship between the spin structure function gLT (x,Q ) = g1(x,Q )+ g2(x,Q ), 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 rise gLT (x,Q ) ∼ g2(x,Q) ∼ ( 1 x )2(1+δg) , where δg 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 ∼ mf for heavy flavour contribution. It invalidates the BurkhardtCottingham sum rule. The found small-x rise of diffraction driven gLT (x,Q ) is steeper than given by the Wandzura-Wilczek relation under conventional assumptions on small-x behaviour of g1(x,Q ).