Gluon polarization from QCD sum rules

The gluon polarization ΔG in a nucleon can be defined in a gauge invariant way as the integral over the Ioffe-time distribution of polarized gluons. We argue that for sufficiently regular polarized gluon distributions ΔG is dominated by contributions from small and moderate values of the Ioffe-time z ≲ 10. As a consequence ΔG can be estimated with 20% accuracy from the first two even moments of the polarized gluon distribution, and its behavior at small values of Bjorken x or, equivalently, at large Ioffe-times z. We employ this idea and compute the first two moments of the polarized gluon distribution within the framework of QCD sum rules. Combined with the color coherence hypothesis we obtain ΔG ≈ 2.1 ± 1.0 at a scale μ2 ∼ 1 GeV2.