The infrared stability of the anomalous perturbative gluon contribution to the nucleon spin

We examine the problem of the infrared (in)sensitivity of the perturbative computation of the anomalous gluonic contribution to the first moment of the spin-dependent nucleon structure function g1(x). In the scaling limit, it is possible to isolate unambiguously the hard contribution for quarks which are either much lighter or much heavier than ΛQCD. We obtain the exact formula which interpolates smoothly between these two cases. For light quarks we confirm the results obtained earlier by Altarelli et al. and Carlitz et al. For realistic values of Q2 we find strong scaling violations, which suggest that asymptotic results cannot be directly compared with experimental data. (orig.)