FeynFacet: AI agents for analytic NLO QCD
Abstract
We present FeynFacet, a workflow in which artificial intelligence agents develop and execute programs for analytic next-to-leading-order (NLO) QCD calculations, with the observables and conventions specified by physicists. We use it to derive new analytic hard functions for single-inclusive transverse spin transfer in proton-proton and lepton-proton collisions. The new proton-proton results cover all partonic channels contributing to transverse spin transfer, and the new lepton-proton result is inclusive in the scattered lepton. Within FeynFacet, we use reverse unitarity to represent the on-shell delta functions in real-emission phase-space integrals as cut propagators. Dimensional shifts convert integrals containing evanescent numerators into scalar integrals in higher dimensions. Integration-by-parts identities then reduce the scalar integrals to master integrals, which are evaluated analytically. Gauge invariance, pole cancellation and renormalization-group (RG) evolution provide checks throughout the calculation. We reproduce established single-inclusive hard functions for unpolarized and double longitudinally polarized proton-proton and lepton-proton scattering, and for proton-proton scattering with two transversely polarized beams. We also reproduce the NLO matching coefficients for unpolarized quark and gluon transverse-momentum-dependent parton distributions and the associated soft functions. The new transverse spin-transfer coefficients provide perturbative inputs for extracting quark transversity through spin-dependent fragmentation, including polarized-hyperon production, Collins and dihadron asymmetries in jets, and spin-dependent one- and two-point energy correlators. We make all analytic coefficients and the associated calculation programs publicly available online.
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BibTeX
@misc{kang2026feynfacet,
title = {{FeynFacet: AI agents for analytic NLO QCD}},
author = {Zhong-Bo Kang and Werner Vogelsang and Congyue Zhang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.31745},
eprint = {2610.31745},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.31745},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - FeynFacet: AI agents for analytic NLO QCD
AU - Zhong-Bo Kang
AU - Werner Vogelsang
AU - Congyue Zhang
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.31745
UR - https://arxiv.org/abs/2610.31745
AB - We present FeynFacet, a workflow in which artificial intelligence agents develop and execute programs for analytic next-to-leading-order (NLO) QCD calculations, with the observables and conventions specified by physicists. We use it to derive new analytic hard functions for single-inclusive transverse spin transfer in proton-proton and lepton-proton collisions. The new proton-proton results cover all partonic channels contributing to transverse spin transfer, and the new lepton-proton result is inclusive in the scattered lepton. Within FeynFacet, we use reverse unitarity to represent the on-shell delta functions in real-emission phase-space integrals as cut propagators. Dimensional shifts convert integrals containing evanescent numerators into scalar integrals in higher dimensions. Integration-by-parts identities then reduce the scalar integrals to master integrals, which are evaluated analytically. Gauge invariance, pole cancellation and renormalization-group (RG) evolution provide checks throughout the calculation. We reproduce established single-inclusive hard functions for unpolarized and double longitudinally polarized proton-proton and lepton-proton scattering, and for proton-proton scattering with two transversely polarized beams. We also reproduce the NLO matching coefficients for unpolarized quark and gluon transverse-momentum-dependent parton distributions and the associated soft functions. The new transverse spin-transfer coefficients provide perturbative inputs for extracting quark transversity through spin-dependent fragmentation, including polarized-hyperon production, Collins and dihadron asymmetries in jets, and spin-dependent one- and two-point energy correlators. We make all analytic coefficients and the associated calculation programs publicly available online.
ER -