Dynamical Parton Distributions Revisited

TL;DR

This paper revisits the dynamical parton model, where parton densities at small $x$ and moderate $Q^2$ arise radiatively from valence-like inputs at a low scale, to test against the latest HERA and fixed-target data.Using exact numerical solutions for the NLO running coupling and a carefully tuned input at $\mu^2 \approx 0.3-0.4$ GeV$^2$, the authors generate LO and NLO parton densities with $\alpha_s(M_Z^2)=0.114$.They show that the updated densities remain compatible with $F_2$ and related observables, refine the small-$x$ behavior of gluons and sea, and extend predictions to extremely small $x$ ($10^{-8}$ to $10^{-5}$) relevant for ultra-high-energy neutrino interactions.They also test against a wide set of data including $F_2^c$, Drell–Yan, and W asymmetries, and provide a parameter-free, perturbatively stable framework for deriving cross sections in regimes inaccessible to current experiments.

Abstract

Dynamical parton densities, generated radiatively from valence-like inputs at some low resolution scale, are confronted with recent small-x data on deep inelastic and other hard scattering processes. It is shown that within theoretical uncertainties our previous (1994) dynamical/radiative parton distributions are compatible with most recent data and still applicable within the restricted accuracy margins of the presently available next-to-leading order calculations. Due to recent high precision measurements we also present an updated, more accurate, version of our (valence-like) dynamical input distributions. Furthermore, our perturbatively stable parameter-free dynamical predictions are extended to the extremely small-x region, 10^-8 ~< x ~< 10^-5, relevant to questions concerning ultra-high-energy cosmic ray and neutrino astronomy.