Large-x power laws of parton distributions remain inconclusive

TL;DR

This paper investigates the large-x behavior of parton distribution functions, comparing theoretical predictions with phenomenological data, and finds significant uncertainties that prevent conclusive determination of the asymptotic power laws.

Contribution

It provides a detailed comparison between nonperturbative QCD predictions and phenomenological PDFs, highlighting uncertainties in the large-x asymptotic behavior.

Findings

Uncertainties of about one unit in the effective powers of (1-x) falloff.

Similar uncertainties are observed for the pion PDF.

Current data and models do not conclusively determine large-x power laws.

Abstract

Focusing on hadron scattering at large partonic momentum fractions $x$, we compare nonperturbative QCD predictions for the asymptotic behavior of DIS structure functions and parton distribution functions (PDFs) to the $x$ and $Q$ dependence of phenomenological PDFs. In the CT18 NNLO global QCD analysis, higher-order radiative contributions and functional mimicry of PDF parametrizations result in about one unit of uncertainty in the effective powers of $(1-x)$ falloff of nucleon PDFs. Similar uncertainties are present in the case of the pion PDF, an object of growing interest in phenomenology.