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Intrinsic properties of large CP violation in the complex two-Higgs-doublet model

Soojin Lee1,2,*, A. Hammad3,†, Dongjoo Kim4,‡, and Jeonghyeon Song4,§

  • *Contact author: soojin.lee@gapp.nthu.edu.tw
  • †Contact author: hamed@post.kek.jp
  • ‡Contact author: dongjookim.phys@gmail.com
  • §Contact author: jhsong@konkuk.ac.kr
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Phys. Rev. D 113, 115034 – Published 15 June, 2026

DOI: https://doi.org/10.1103/f6hb-dxhp

Abstract

We investigate the parameter space supporting large CP violation (CPV) in the complex two-Higgs-doublet model with softly broken Z2 symmetry, where the 125 GeV Higgs boson is identified as the lightest neutral Higgs boson H1. Through a comprehensive global scan of type-I and type-II models under theoretical, collider, and eEDM constraints, we identify distinct structures that facilitate large CPV. In type-I, gauge-sector CPV is maximized when the 125 GeV Higgs boson is nearly degenerate with a second neutral scalar. For the ensemble of physically viable points, the predicted eEDM values typically exceed 10−31  e cm, placing the model largely within the sensitivity of next-generation experiments. Conversely, type-II models strongly suppress gauge-sector CPV while allowing for nearly maximal CPV in the Yukawa sector. Destructive interference among various contributions allows for |de| values as low as O(10−35)  e cm, resulting in no phenomenologically relevant lower bound. Finally, we uncover the phenomenon of “hidden CPV” in the near-alignment limit, characterized by CP-violating mixing between the heavy neutral Higgs bosons governed by the angle α3. We demonstrate that this hidden CPV can be experimentally probed at future colliders via CP-violating Yukawa interactions of H2 and H3, as well as the robust H2−H3−Z coupling.

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Outline

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Phys. Rev. D 113, 115034– Published 15 June, 2026
  • Received 26 December 2025
  • Accepted 19 May 2026
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