Comments on Global Parton Analyses

TL;DR

This paper analyzes limitations in global parton distribution function analyses, focusing on power corrections, BFKL resummation effects, and heavy-quark threshold treatments, proposing methods to improve accuracy.

Contribution

It introduces a method to include heavy-quark masses in DGLAP evolution and addresses double counting issues in NLO coefficient functions.

Findings

Proper inclusion of heavy-quark masses yields smooth threshold behavior.

Subtracting low virtuality contributions avoids double counting.

Discusses the impact of power corrections and BFKL resummation on PDF accuracy.

Abstract

We discuss the causes which can limit the accuracy of the predictions based on the conventional PDFs when including in global parton analyses the data at moderate scales $\mu$. The first is the existence of power corrections ${\cal O} (Q_0^2/\mu^2)$ due to the double counting of contributions arising from the region below the input scale $Q_0$. The second concerns the possible inclusion of the BFKL re-summation of the $(\alpha_s\ln (1/x))^n$ terms. The third is the treatment of the heavy-quark thresholds. We show how to include the heavy-quark masses ($m_h$ with $h=c,b,t$) in DGLAP evolution which provides the correct {\it smooth} behaviour through the threshold regions and how to subtract the low parton virtuality $|k^2|<Q^2_0$ contributions from the DIS and Drell-Yan NLO coefficient functions in order to avoid the double counting.