The Proton Spin Problem

The proton (and neutron) are supposed to be composed of quarks and gluons. The spin of the proton is known. It would be nice to be able to calculate the spin based on the physics of its components - presumably the Standard Model of particle physics. This has proved difficult. Here's a recent preprint discussing the problem:

Resolution of the Proton Spin Problem
Authors: F. Myhrer, A.W. Thomas
(Submitted on 26 Sep 2007)
Abstract: A number of lines of investigation into the structure of the nucleon have converged to the point where we believe that one has a consistent explanation of the well known proton spin crisis.

preprint