Orbital Angular Momentum on the Light-Front and QCD Observables

The light-front wavefunction formalism provides a physical, but rigorous, representation for angular momentum in a relativistic quantum field theory. Each n-particle LFWF {psi}{sub n}(x{sub i}, {rvec k}{sub {perpendicular}}i,S{sub i}{sup z}) in the Fock state expansion of a hadron in QCD is frame-independent and satisfies angular momentum conservation J{sup z} = {summation}{sub i=1}{sup n} S{sub i}{sup z} + {summation}{sub i=1}{sup n-1} L{sub i}{sup z}, summed over the n - 1 independent intrinsic orbital angular momenta L{sub i}{sup z} = -i [{rvec k}{sub i}{sup x} {partial_derivative}/{partial_derivative}k{sub i}{sup y} - {rvec k}{sub i}{sup y} {partial_derivative}/{partial_derivative}k{sub i}{sup x}]. Gluons propagate with physical polarization S{sub g}{sup z} = {+-} 1 in light-cone gauge A{sup +} = 0. All of these features are illustrated by the Fock state expansion of the electron in terms of its fermion-boson components