Photon-Parton Splitting Functions at the Next-to-Next-to-Leading Order of QCD

TL;DR

This paper presents the calculation of photon-parton splitting functions at NNLO in QCD, providing precise parametrizations and confirming small corrections at moderate momentum fractions.

Contribution

It provides the first complete NNLO calculation of photon-parton splitting functions, improving the accuracy of photon structure evolution models.

Findings

NNLO corrections are small for x >~ 0.1

Results are consistent with previous Mellin moment approximations

Parametrizations are accurate and compact

Abstract

We have calculated the splitting functions governing the evolution of the unpolarized parton distributions of the photon at the next-to-next-to-leading order (NNLO) of massless perturbative QCD. The results, presented here mainly in terms of compact and accurate parametrizations, are consistent with our previous approximations based on the lowest six even-integer Mellin moments. Consequently the NNLO corrections are small in both the MSbar and the DIS_gamma factorization schemes at momentum fractions x >~ 0.1.