Evolution of Gluon Spin in the Nucleon

Abstract

We examine the $Q^2$ evolution of gluon polarization in polarized nucleons. As is well known, the evolution of $\alpha_s \Delta G(Q^2)$ is negligible for typical momentum transfer variations found in experimental deep inelastic scattering. As $\alpha_s$ increases, however, the leading nonzero term in the evolution equation for the singlet first moment reduces the magnitude of the gluon spin. At low $Q^2$ the term $\alpha_s \Delta G$ can vanish, and ultimately become negative. Thus, low energy model calculations yielding negative $\Delta G$ are not necessarily in conflict with experimental evidence for positive gluon polarization at high $Q^2$.