NONSINGLET CONTRIBUTIONS TO THE STRUCTURE-FUNCTION G(1) AT SMALL-X

Nonsinglet contributions to the g(1)(x, Q(2)) structure function are c alculated in the double-logarithmic approximation of perturbative QCD in the region x much less than 1. Double logarithmic contributions of the type (alpha(s) ln(2) (1/x))(k) which are not included in the GLAP evolution equations are shown to give a stronger rise at small-x than the extrapolation of the GLAP expressions. Further enhancement in the small-x region is due to non-ladder Feynman graphs which in the DLA of the unpolarized structure functions do not contribute. Compared to th e conventional GLAP method (where neither the whole kinematical region which gives the double logs nor the non-ladder graphs are taken into account) our results lead to a growth at small-x which, for HERA param eters, can be larger by up to factor of 10 or more.