FLAVOR SINGLET CONTRIBUTION TO THE STRUCTURE-FUNCTION G(1) AT SMALL-X

The singlet contribution to the g(1)(x, Q(2)) structure function is ca lculated in the double-logarithmic approximation of perturbative QCD i n the region x much less than 1. Double logarithmic contributions of t he type (alpha(s) ln(2) (1/x))(k) which are not included in the GLAP e volution equations are shown to give a power-like rise at small-x whic h is much stronger than the extrapolation of the GLAP expressions. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the region x much less than 1. The two main reasons why the small-x behavior of the double l ogarithmic approximation is so much stronger than the usual GLAP evolu tion are: the larger kinematical region of integration (in particular, no ordering in transverse momentum) and the contributions from non-la dder diagrams.