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arXiv · 2610.07233

Toward N$^3$LO CT global PDF analyses: The SACOT-$χ$ scheme in DIS and DGLAP evolution at partial N$^3$LO

Marco Guzzi·Yao Fu·Casey Hampson·Pavel Nadolsky·Maximiliano Ponce-Chavez·Tanishq Sharma·Keping Xie·C. -P. Yuan
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Abstract

We discuss three aspects of the ongoing efforts of the CTEQ--TEA group toward global parton distribution function (PDF) analyses beyond NNLO accuracy in QCD. First, we present a realization of the SACOT-$χ$ general-mass variable flavor number scheme for deep-inelastic scattering (DIS) at the partial next-to-next-to-next-to-leading order (pN$^3$LO) in QCD. We numerically illustrate how this SACOT-$χ$ theory prediction captures the dependence of DIS structure functions on masses of heavy quarks with inclusion of the available $O(α_s^3)$ contributions. Second, we discuss a preliminary pN$^3$LO CT25 fit that implements such contributions. Third, we extend the Candia algorithm for solving DGLAP evolution equations for unpolarized parton distribution functions (PDFs) in $x$ space to N$^3$LO in QCD. The algorithm is based on logarithmic expansions of the solution and can be extended to all orders in QCD. An expansion equivalent to the exact DGLAP solution at N$^3$LO is presented in the non-singlet sector. We show results for approximate N$^3$LO PDFs evolved using the most recent approximations to the 4-loop splitting functions in QCD.

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Marco Guzzi, Yao Fu, Casey Hampson, Pavel Nadolsky, Maximiliano Ponce-Chavez, Tanishq Sharma, Keping Xie, C. -P. Yuan. 2026-10-05. Toward N$^3$LO CT global PDF analyses: The SACOT-$χ$ scheme in DIS and DGLAP evolution at partial N$^3$LO. https://arxiv.org/abs/2610.07233

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