Spin structure functions of the nucleon and twist-3 operators in QCD

The author investigates the twist-3 spin-dependent parton distribution functions HL(x,Q2) and gT(x,Q2), and discuss the physical relevance of the parton distributions from the point of view of the factorization theorem in QCD. A unique feature of the 'measurable' higher-twist distributions hL and gT is emphasized. The Q2-evolution of hL and gT in the framework of the renormalization group and standard QCD perturbation theory are also investigated and the anomalous dimension matrix for the twist-3 operators for hL and gT in the one-loop order is calculated. The operator mixing among the relevant twist-3 operators, including the operators proportional to the QCD equations of motion, is treated properly in a consistent scheme. Implications for future experiments are then discussed. 24 refs., 9 figs