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Toward the determination of CP-odd pion-nucleon couplings

Shohini Bhattacharya1,2,*, Kaori Fuyuto2,†, Emanuele Mereghetti2,‡, and Thomas R. Richardson3,4,§

  • *Contact author: shohinib@uconn.edu
  • †Contact author: kfuyuto@lanl.gov
  • ‡Contact author: emereghetti@lanl.gov
  • §Contact author: thomas.richardson@berkeley.edu
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Phys. Rev. C 112, 025501 – Published 20 August, 2025

DOI: https://doi.org/10.1103/fhm8-flsg

Abstract

The nucleon matrix elements (NMEs) associated with quark chromomagnetic dipole moments (cMDMs) play a crucial role in determining the CP-odd pion-nucleon couplings induced by quark chromoelectric dipole moments. In recent years, it has been argued that the NMEs of cMDMs can be related to the third moment of the nucleon's higher-twist (specifically, twist-3) parton distribution function (PDF) e(x), which can, in principle, be measured through dihadron production in semi-inclusive deep inelastic scattering processes. By applying the spin-flavor expansion to the cMDM operators in the large-Nc limit, where Nc is the number of quark colors, we show that the NMEs receive contributions not only from the twist-3 PDF e(x) but also from an additional, previously neglected nucleon form factor. Incorporating constraints from the spin-flavor expansion, recent experimental data on e(x), as well as model calculations of e(x), we estimate the NMEs of the cMDM operators. Our analysis indicates that the NMEs are dominated by the nucleon form factors, and the cMDM contributions to pion-nucleon couplings can be comparable to those from the quark sigma terms.

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Phys. Rev. C 112, 025501– Published 20 August, 2025
  • Received 10 April 2025
  • Accepted 16 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

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