The singlet contribution to the structure function g1(x,Q2) at small x

The resummation of O(αsl+1ln2lx) terms in the evolution of the singlet part of g1(x,Q2) is carried out on the basis of the renormalization group equation. The corresponding singlet anomalous dimensions are calculated explicitly referring to amplitude relations derived by Bartels et al. [J. Bartels, B.I. Ermolaev and M.G. Ryskin, DESY 96-025]. The leading small-x contribution to the three-loop splitting function matrix is determined in the MS scheme. Relations are derived for the case of N = 1 supersymmetric Yang-Mills field theory. Numerical results are presented for the polarized singlet and gluon densities, and the structure functions g1p(x,Q2) and g1n(x,Q2). They are compared for different assumptio the non-perturbative input distributions, and the stability of the results against presently unknown subleading contributions is investigated.