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Strong CP violation and large-Nc spin-flavor symmetry

Thomas R. Richardson1,*

  • *Contact author: thomas.richardson@berkeley.edu
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Phys. Rev. D 112, 095045 – Published 25 November, 2025

DOI: https://doi.org/10.1103/1jb4-tqpn

Abstract

We revisit the contribution of the QCD θ¯ term to the CP-violating pion-nucleon couplings and the nucleon electric dipole moment in a combined large-Nc and chiral perturbation theory framework. In particular, we approach this issue through the emergent spin-flavor symmetry of the baryon sector at large but finite Nc. We obtain good agreement with previous analyses for the pion-nucleon couplings and show that the large-Nc framework indicates that tree-level contributions to the electric dipole moment possibly play a dominant role. The spin-flavor symmetry also enables us to provide novel constraints on CP-violating pion-Δ couplings, as well as the Δ electric dipole moment and ΔN transition moment.

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Phys. Rev. D 112, 095045– Published 25 November, 2025
  • Received 9 September 2025
  • Accepted 7 November 2025
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