The Trace Anomaly and the Parton Model

The trace anomaly is relevant to the renormalisation of the unpolarised parton distributions. The coefficient which describes the local γ∗(glue) interaction differs at next-to-leading order between the renormalised operator product expansion and parton model descriptions of deep inelastic scattering – independent of the factorisation scheme. There are two approaches to the theory of deep inelastic scattering (DIS). These are the operator product expansion (OPE) and the QCD improved parton model (PM) [1]. In both approaches we write the transverse and longitudinal structure functions as the sum over the convolution of soft quark and gluonic parton distributions with hard coefficients, viz.