Dynamical parton distribution functions

TL;DR

This paper analyzes recent F_2 measurements using dynamical and standard parton models at NLO and NNLO, showing that the dynamical approach yields more stable predictions for the longitudinal structure function F_L(x,Q^2).

Contribution

It demonstrates that the dynamical parton distributions lead to stable F_L(x,Q^2) predictions, resolving the perturbative instability seen with standard distributions.

Findings

Dynamical parton distributions produce stable F_L(x,Q^2) at low Q^2.

Standard distributions exhibit perturbative instability in F_L(x,Q^2).

Predictions are consistent at NLO and NNLO for Q^2 ≥ 2-3 GeV^2.

Abstract

Recent measurements for F_2(x,Q^2) have been analyzed in terms of the `dynamical' and `standard' parton model approach at NLO and NNLO of perturbative QCD. Having fixed the relevant NLO and NNLO parton distributions, the implications and predictions for the longitudinal structure function F_L(x,Q^2) are presented. It is shown that the previously noted extreme perturbative NNLO/NLO instability of F_L(x,Q^2) is an artifact of the commonly utilized `standard' gluon distributions. In particular it is demonstrated that using the appropriate -- dynamically generated -- parton distributions at NLO and NNLO, F_L(x,Q^2) turns out to be perturbatively rather stable already for Q^2 \geq O(2-3 GeV^2).