Dynamical parton distribution functions

Recent measurements for F2(x, Q ) 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 FL(x,Q ) are presented. It is shown that the previously noted extreme perturbative NNLO/NLO instability of FL(x, Q ) 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, FL(x,Q ) turns out to be perturbatively rather stable already for Q ≥ O (2− 3 GeV).