Dynamical parton distributions of the nucleon and very small-x physics

Utilizing recent DIS measurements (F2,L) and data on dilepton and high–ET jet production we determine the dynamical parton distributions of the nucleon generated radiatively from valence–like positive input distributions at optimally chosen low resolution scales. These are compared with ‘standard’ distributions generated from positive input distributions at some fixed and higher resolution scale. It is shown that up to the next to leading order NLO(MS, DIS) of perturbative QCD considered in this paper, the uncertainties of the dynamical distributions are, as expected, smaller than those of their standard counterparts. This holds true in particular in the presently unexplored extremely small–x region relevant for evaluating ultrahigh energy cross sections in astrophysical applications. It is noted that our new dynamical distributions are compatible, within the presently determined uncertainties, with previously determined dynamical parton distributions. ar X iv :0 70 9. 06 14 v1 [ he pph ] 5 S ep 2 00 7