Singlet contribution to the structure function g(sub 1)(x,Q(sup 2)) at small x

摘要

The resummation of O((alpha)(sub s)(sup l+1)ln(sup 2l)x) terms in the evolution equation of the singlet part of g(sub 1)(x,Q(sup 2)) is carried out. The corresponding singlet evolution kernels are calculated explicitely. The leading small-x contribution to the three-loop splitting function matrix is determined in the anti M anti S 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 g(sub 1)(sup p)(x,Q(sup 2)) and g(sub 1)(sup n)(x,Q(sup 2)). They are compared for different assumptions on the non-perturbative input distributions, and the stability of the results against presently unknown subleading contributions is investigated. (orig.)