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Electromagnetic structure of axial-vector mesons and implications for the muon g−2

Zanbin Xing1,*, Lei Chang1,†, and Khépani Raya2,‡

  • 1School of Physics, Nankai University, Tianjin 300071, China
  • 2Department of Integrated Sciences and Center for Advanced Studies in Physics, Mathematics and Computation, University of Huelva, E-21071 Huelva, Spain

  • *Contact author: xingzb@mail.nankai.edu.cn
  • †Contact author: leichang@nankai.edu.cn
  • ‡Contact author: khepani.raya@dci.uhu.es
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Phys. Rev. D 113, 034010 – Published 5 February, 2026

DOI: https://doi.org/10.1103/xbls-4zqr

Abstract

The electromagnetic structure of axial-vector mesons is investigated via elastic and two-photon transition form factors (TFFs). To this end, we employ a framework based on the Dyson-Schwinger and Bethe-Salpeter equations within a contact interaction (CI) model. This largely algebraic approach exposes the role of symmetries and their breaking in a transparent manner, and has proven successful in describing anomaly-sensitive processes, including pseudoscalar to two-photon TFFs, γ→3π, and vector-to-pseudoscalar radiative decays. Restricting our analysis to the lowest-lying axial-vector meson multiplet, A={a1,f1,f1′}, we also explore the corresponding light-by-light contribution to the muon anomalous magnetic moment. This contribution is underestimated in the CI model mainly due to the normalization of the TFFs. After applying a phenomenologically motivated rescaling to the TFFs, a process required given the limitations of the CI model, we obtain aμA=8.16−1.02+1.22×10−11, consistent with contemporary assessments.

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Phys. Rev. D 113, 034010– Published 5 February, 2026
  • Received 18 November 2025
  • Accepted 16 January 2026
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