Nucleon spin structure and its connections to various sum rules

Our knowledge on the nucleon spin structure has greatly improved over the last twenty years or so, but still many fundamental questions remain unsolved. I will try to review some of the puzzling aspects of the origin of the nucleon spin. I will emphasize the connection with several sum rules and, when using this tool, the relevance of some kinematic regions for testing them in the QCD dynamics framework.Comment: 10 pages, 4 figures, Invited talk presented at GDH2004, June 2-5 2004, Old Dominion University, Virginia, US

Positivity domains for pairs of triples of spin observables

Positivity restrains the allowed domains for pairs or triples of spin observables in polarised reactions. Various domain shapes in ${1\over2}+{1\over2}\to{1\over2}+{1\over2}$ reactions are displayed. Some methods to determine these domains are mentioned and a new one based on the anticommutation between two observables is presented.Comment: Talk given by Xavier Artru at "DSPIN-07", XII Workshop on High-Energy Spin Physics, Dubna, Sept. 3-7, 2007, to appear in the Proceeding

A statistical approach for polarized parton distributions

A global next-to-leading order QCD analysis of unpolarized and polarized deep-inelastic scattering data is performed with parton distributions constructed in a statistical physical picture of the nucleon. The chiral properties of QCD lead to strong relations between quarks and antiquarks distributions and the importance of the Pauli exclusion principle is also emphasized. We obtain a good description, in a broad range of $x$ and $Q^2$, of all measured structure functions in terms of very few free parameters. We stress the fact that at RHIC-BNL the ratio of the unpolarized cross sections for the production of $W^+$ and $W^-$ in $pp$ collisions, will directly probe the behavior of the $\bar d(x) / \bar u(x)$ ratio for $x \geq 0.2$, a definite and important test for the statistical model. Finally, we give specific predictions for various helicity asymmetries for the $W^{\pm}, Z$ production in $pp$ collisions at high energies, which will be measured with forthcoming experiments at RHIC-BNL and are sensitive tests of the statistical model for $\Delta \bar u(x)$ and $\Delta \bar d(x)$.Comment: 49 pages, 27 eps figure