1304.6708 (Xiangdong Ji et al.)

Physics of Gluon Helicity Contribution to Proton Spin    [PDF]

Xiangdong Ji, Jian-Hui Zhang, Yong Zhao

The total gluon helicity in a polarized proton, measurable in high-energy scattering, is shown to be the large momentum limit of a gauge-invariant but non-local, frame-dependent gluon spin $\vec{E}\times \vec{A}_\perp$ in QCD. This opens a door for a non-perturbative calculation of this quantity in lattice QCD, and also justifies using free-field expressions in the light-cone gauge as physical observables.

View original: http://arxiv.org/abs/1304.6708