Polarized gluon distribution Δg(x)Δg(x) in the proton

We study the polarized gluon distribution Δg(x)Δg(x) in a longitudinally polarized proton. We argue that the distribution can be calculated approximately from the quark color currents found in simple quark models. The first result from the MIT bag model as well as the non-relativistic quark model shows that Δg(x)Δg(x) is positive at all x. If this feature holds in QCD, it imposes a strong constraint on phenomenological fits to experimental data. The total gluon helicity ΔG from the bag model is about 0.3ℏ at the scale of 1 GeV, considerably smaller than previous theoretical expectations.