Polarized parton distributions and the polarized gluon asymmetry.

The flavor-dependent valence, sea quark and antiquark spin distributions can be determined separately from theoretical assumptions and experimental data. The authors have determined the valence distributions using the Bjorken sum rule and have extracted polarized sea distributions, assuming that the quarks and anti-quarks for each flavor are symmetric. Other experiments have been proposed which will allow them to completely break the SU(3) symmetry of the sea flavors. To create a physical model for the polarized gluons, they investigate the gluon spin asymmetry in a proton, A{sub G}(x,Q{sup 2}) = {Delta}G(x,Q{sup 2})/G(x,Q{sup 2}). By assuming that this is approximately Q{sup 2} invariant, they can completely determine the x-dependence of this asymmetry, which satisfies constituent counting rules and reproduces the basic results of the Bremsstrahlung model originated by Close and Sivers. This asymmetry can be combined with the measured unpolarized gluon density, G(x,Q{sup 2}) to provide a prediction for {Delta}G(x,Q{sup 2}). Existing and proposed experiments can test both the prediction of scale-invariance for A{sub G}(x,Q{sup 2}) and the nature of {Delta}G itself. These models can be discussed along with suggestions for specific experiments which can be performed at energies typical of HERA, RHIC and LHC to determine these polarized distributions