Implications of color gauge symmetry for nucleon spin structure - art. no.074010

We study the chromodynamical gauge symmetry in relation to the internal spi n structure of the nucleon. We show that (1) even in the helicity eigenstat es the gauge-dependent spin and orbital angular momentum operators do not h ave gauge-independent matrix element, (2) the evolution equations for the g luon spin take very different forms in the Feynman and axial gauges, but yi eld the same leading behavior in the asymptotic limit, and (3) the complete evolution of the gauge-dependent orbital angular momenta appears intractab le in the light-cone gauge. We define a new gluon orbital angular momentum distribution L-g(x) which is an experimental observable and has a simple sc ale evolution. However, its physical interpretation makes sense only in the light-cone gauge just like the gluon helicity distribution Delta g(x). [S0 556-2821(99)02207-9].