Conformal Mapping in Matching Quark Correlation Functions to Parton Distribution Functions

Abstract

In high-energy particle physics, extracting parton distribution functions (PDFs) from lattice quantum chromodynamics (QCD) calculations remains a significant challenge, particularly due to the divergent nature of perturbative expansions at high orders. The presence of renormalon singularities in the Borel plane further hinders the accurate determination of PDFs, especially in the context of lattice QCD and effective field theory approaches like Large Momentum Effective Theory (LaMET). This study explores the application of conformal mapping as a technique to improve the convergence of perturbative series for matching kernels. By transforming the Borel plane to map singularities onto the unit disk, this method mitigates the effects of divergent behavior in high-order perturbative expansions of matching kernels. The numerical analysis focuses on the matching kernel for quark correlation functions (QCFs), using the CT18NNLO PDFs for u-quarks and d-quarks, along with N3LO hard kernel inputs. The results demonstrate that conformal mapping enhances the stability of the perturbative series, reducing the root-mean-square (RMS) error by up to $40\%$ compared to conventional $\alpha_s$ series. These findings highlight the potential of conformal mapping to enhance the precision of PDFs and reduce theoretical uncertainties in high-order QCD calculations.