[論文レビュー] CP-violation and its implications in a complex singlet extension of 2HDM

Jayita Lahiri, Gudrid Moortgat-Pick|arXiv (Cornell University)|Mar 23, 2026

Particle physics theoretical and experimental studies被引用数 0

ひとこと要約

This paper analyzes CP-violation in a complex singlet extension of the general 2HDM with Yukawa alignment, including dark matter and EDM constraints, and explores collider probes of CP-violating effects.

ABSTRACT

We investigate CP-violation in the complex singlet extension of the general Two Higgs Doublet Model (2HDM) with Yukawa alignment condition. We first explore the possibility of explicit CP-violation in the extended scalar sector while the 125 GeV Higgs remains exactly Standard Model (SM)-like. We identify an additional source of CP violation in the complex singlet extension compared to the 2HDM, which allows this model a substantially greater freedom in satisfying the stringent EDM constraints. We also incorporate dark matter in this model and investigate the impacts of constraints from the dark sector on the model parameter space and its interplay with CP-violation phases. We further explore the possibility of detecting such a scenario at future collider experiments via CP-violating trilinear couplings among the non-standard scalars. Finally, we also deviate from the exact alignment limit and investigate the CP-properties of the observed Higgs boson in the context of our model. We demonstrate the strong model-dependent nature of the detection prospects of the CP-phase of the Higgs boson at future experiments, exploring both fermion couplings as well as the trilinear self-coupling of the Higgs boson.

研究の動機と目的

• Motivate CP-violation beyond the SM to address baryogenesis and DM within an extended scalar sector.
• Introduce and analyze the complex singlet extension of the 2HDM with Yukawa alignment under exact alignment.
• Identify CP-violating sources in the scalar potential and Yukawa sector and their physical effects.
• Assess EDM, dark matter, and collider constraints on the model parameter space.
• Explore CP-violating signatures in non-standard scalars and in the 125 GeV Higgs away from exact alignment.

提案手法

• Set up the most general potential for two Higgs doublets plus a complex singlet with possible complex parameters.
• Work in the Higgs basis to derive the scalar mass matrix and identify CP-violating phases.
• Impose exact alignment to keep a SM-like 125 GeV Higgs while allowing CP-violation in the scalar sector.
• Implement Yukawa alignment to avoid FCNCs while permitting CP-violating phases from Yukawa couplings.
• Incorporate a dark matter candidate from the complex singlet and derive stability conditions and mass relations.
• Compute EDM contributions via two-loop Bar-Zee diagrams including fermion, scalar, and gauge-boson loops and compare with experimental bounds.

Figure 1 : The two-loop Bar-Zee diagrams with fermion (left), scalar (middle) and gauge-boson (right) loop contributions. The solid lines with pointing arrows denote fermion lines (quarks and leptons), the dashed lines denote scalars ( $H_{1..4}$ and $H^{\pm}$ ), and the wavy lines represent gauge b

実験結果

リサーチクエスチョン

• RQ1 What sources of CP-violation arise in the complex singlet extension of the 2HDM with Yukawa alignment?
• RQ2 How does EDM data constrain the CP-violating phases and scalar masses in this model?
• RQ3 Can the model accommodate a dark matter candidate without spoiling alignment or inducing large EDMs?
• RQ4 What are the prospects for detecting CP-violating effects at future colliders through trilinear couplings and Higgs couplings?
• RQ5 How does the CP-phase of the 125 GeV Higgs behave when moving beyond exact alignment within this framework?

主な発見

• The model introduces an additional CP-violating phase, theta_CP, in the scalar mass matrix beyond the CP-violating phase in standard 2HDM extensions, enabling more freedom to satisfy EDM constraints.
• Electron EDM constraints can be satisfied via cancellations between fermion and scalar loop contributions, with the allowed region depending on non-standard scalar masses and couplings like lambda_5′ and lambda_2′.
• With the extra CP-violating source theta_CP, the EDM constraints are substantially relaxed compared to CP-violating 2HDMs, broadening the viable parameter space.
• The complex singlet extension permits a stable dark matter candidate under specific real/imaginary parts relations among lambda′ terms, including lambda_6′, lambda_7′, and lambda_8′, while maintaining alignment.
• CP-violating signatures can arise in CP-violating trilinear and quadrilinear scalar couplings (e.g., involving theta_7) even when the 125 GeV Higgs is SM-like, and the detection prospects at future colliders are highly model-dependent.

Figure 2 : Constraints on $\theta_{CP}$ from the most recent electron EDM bound with $\theta_{7}=0,\theta_{f}=0$ , $|\lambda_{7}|=0.3,\lambda_{2}^{\prime}=0$ .