Internal Spin Structure of the Nucleon

Quantum chromodynamics provides a theoretical explanation and a physical pic----ture of why the interaction between quarks and gluons would vanish asymptotically at very short distances.This perturbative QCD supports the assumptions of the quark _light cone algebra and the quark-parton model.Even-'more powerfully, as a theory should predict new things, it describes quantitatively the logarithmic rate at which quarks become asymptotically free at short distances.(g-lO)The logarithmic corrections to the scaling functions and sum rules are the most important new predictions of perturbative &CD.In particular, the scaling behavior of spin-dependent structure functions and the corrections to it are accurately predicted in &CD together with some important sum rules of the scaling functions.The calculation of the quark and gluon spin distributions inside the nucleon is a difficult nonperturbative calculation.As yet it has not been possible to calculate spindependent (or spin-independent) structure functions from the basic equations of &CD.However, models of nucleon structure have been developed consistent with the general picture of &CD, which make quantitative predictions of the structure functions.In atomic and nuclear physics it has often been found that spin-dependent observables provide particularly sensitive tests of a system's wave function, and we may anticipate that for the nucleon also spin-dependent quantities will be illuminating.We may remark that an enormous theoretical literature on the spin-dependent structure functions of the nucleon has developed since about 1970.