How unitarity imposes a steep small-x rise of spin structure function g(LT)=g(1)+g(2) and breaking of DIS sum rules

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 st ructure function and the spin-flip coupling of the pomeron to nucleons. Our diffractive mechanism gives rise to a dramatic small-x rise g(LT)(x,Q(2)) similar to g(2)(x,(Q) over bar(2)) similar to (1/x)(2(1+delta g)), where de lta(g) is an exponent of small-x rise of the unpolarized gluon density in t he proton g(x,(Q) over bar(2)) at a moderate hard scale (Q) over bar(2) for light flavour contribution and large hard scale (Q) over bar(2) similar to m(f)(2) for heavy flavour contribution. It invalidates the Burkhardt-Cotti ngham 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 a ssumptions on small-x behaviour of g(1)(x,Q(2)). (C) 1999 Elsevier Science B.V. All rights reserved.