Parton densities and structure functions beyond the next-to-leading order

Abstract

We briefly discuss recent results on the evolution of unpolarized parton densities and structure functions in massless perturbative QCD. Present partial results on the next-to-next-to-leading order (NNLO) evolution kernels prove sufficient for reliable calculations at not too small values of the Bjorken variable, x > 10^-3. One order more can be taken into account at x >= 0.2. Inclusion of these terms considerably reduces the main theoretical uncertainties of determinations of alpha_s (to about 1% at the Z-mass) and the parton densities from structure functions.

Comments: 6 pages LaTeX including 6 eps-figures. Talk presented at `Loops and Legs in Quantum Field Theory', Bastei (Germany) April 2000. To appear in the proceedings [Nucl. Phys. B (Proc. Suppl.)]