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  • Letter
  • Open Access
  • Access by Xinjiang University

Universal seesaw mechanism for fermion masses and strong CP problem

Pavel Fileviez Pérez1 and Clara Murgui2,*

  • 1Physics Department and Center for Education and Research in Cosmology and Astrophysics, Case Western Reserve University, Cleveland, Ohio 44106, USA
  • 2Theoretical Physics Department, CERN, 1 Esplanade des Particules, CH-1211 Geneva 23, Switzerland

  • *Contact author: pxf112@case.edu, clara.murgui@cern.ch
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Phys. Rev. D 114, L091702 – Published 12 November, 2026

DOI: https://doi.org/10.1103/1vbs-h2h2

Abstract

We propose a framework for fermion mass generation based on a universal seesaw. The Standard Model is extended by an Abelian gauge symmetry acting on right-handed fermions, together with vectorlike fermions and scalar fields. The ordinary Yukawa couplings are forbidden, except for the top-quark coupling to the Higgs, which is allowed at the renormalizable level and remains unsuppressed. The charged-fermion hierarchies then arise from mixing with the vectorlike sector, and light neutrino masses emerge from a neutral sector Majorana seesaw. CP is exact in the ultraviolet and broken spontaneously by scalar vacuum expectation values. The resulting CP-violating phase is transmitted to the quark sector and generates the Cabibbo-Kobyashi-Maskawa (CKM) phase, while a Nelson-Barr structure, realized through the universal seesaw block form, keeps the physical QCD vacuum angle zero at tree level. Consistency with electric dipole moment (EDM) bounds beyond tree level requires moderately suppressed Yukawa couplings between SM doublets to the vectorlike sector. If the leading higher-dimensional operators are unsuppressed, the same requirement can favor a low breaking scale for the new Abelian symmetry. In this regime the vectorlike fermions can lie at the TeV scale, with suppressed mixing with the electroweak sector. This framework provides a simple setting in which the hierarchies of charged-fermion masses, neutrino masses, and CP-violating parameters can be accounted for within a common extension of the Standard Model.

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Phys. Rev. D 114, L091702– Published 12 November, 2026
  • Received 16 July 2026
  • Accepted 23 October 2026
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