Sum Rules and Positivity Constraints on Nucleon Spin Structure

Abstract

The spin structure of nucleon at twist 2 and 3 levels is analyzed. The contribution of quark and gluon spins to nucleon spin are Lorentz invariant, while it is not sure for orbital angular momentum. The conserved fractional moments of transversity distribution are considered. The scenario of decoupled total angular momentum, determined predominantly by the unpolarized scattering, is discussed.

Comments: LaTeX, 7 pages; Talk at Rencontres de Moriond, March 21-28, 1998