[Paper Review] The CP-violating type-II 2HDM and Charged Higgs boson benchmarks

L. Basso, A. Lipniacka+5 more|arXiv (Cornell University)|May 14, 2013

Particle physics theoretical and experimental studies11 references4 citations

TL;DR

This paper revisits the CP-violating type-II Two-Higgs-Doublet Model (2HDM) with a 125 GeV Higgs boson as the lightest scalar, updating constraints from LHC data including ATLAS and CMS results on Higgs signal strengths. It proposes benchmark scenarios for charged Higgs boson searches via $pp \to H^+W^- \to W^+W^-H_1X$, showing that bosonic-associated channels offer viable discovery prospects despite large top-quark backgrounds due to effective kinematic suppression strategies.

ABSTRACT

We review and update the interpretation of the 125 GeV scalar as the lightest Higgs boson of the Two-Higgs-Doublet Model, allowing for CP violation in the potential. The detection of a charged Higgs boson would exclude the Standard Model. Proposed benchmarks for charged-Higgs searches in the channel pp o H^+W^-X o W^+W^-H_1X are reviewed and updated.

Motivation & Objective

• To reassess the viability of the CP-violating type-II 2HDM in light of updated LHC data from Moriond 2013, particularly the 125 GeV Higgs signal strengths.
• To identify and update benchmark points for charged Higgs boson searches in the $pp \to H^+W^- \to W^+W^-H_1X$ channel under CP-violating conditions.
• To evaluate whether bosonic-associated production of charged Higgs bosons can overcome large top-quark backgrounds through optimized kinematic cuts.
• To ensure theoretical consistency by applying positivity, unitarity, perturbativity, and global minimum constraints to the potential.

Proposed method

• The model is formulated with complex parameters $m_{12}^2$ and $\lambda_5$, allowing CP violation in the scalar potential, with the lightest CP-even Higgs $H_1$ identified as the 125 GeV state.
• The parameter space is scanned using $M_1$, $M_2$, $M^\pm$, $\tan\beta$, and $\mu^2 = \text{Re}(m_{12}^2)/(2\cos\beta\sin\beta)$ as input parameters.
• Theoretical constraints include positivity, tree-level unitarity ($|\lambda_i| < 8\pi$), perturbativity, and global minimum stability.
• Experimental constraints are applied from $R_{\gamma\gamma}$, $R_{VV}$, $B \to \tau\nu$, $\Gamma(Z \to b\bar{b})$, $S$ and $T$ observables, and the electron electric dipole moment.
• The analysis uses a parametrization of the mixing matrix via three angles $\alpha_j$, with approximate relations derived for $\lambda_i$ in terms of masses and $\tan\beta$, enabling efficient scanning.
• Benchmark points are selected based on high production cross sections and favorable decay rates, particularly for $M_{H_2} \sim M_{H^\pm} + M_W$.

Experimental results

Research questions

• RQ1 Can the CP-violating type-II 2HDM remain viable under updated LHC constraints, particularly from $R_{\gamma\gamma}$ and $R_{VV}$?
• RQ2 What are the most promising benchmark scenarios for detecting a charged Higgs boson in the $H^+W^-$ production channel at the LHC?
• RQ3 How does CP violation affect the allowed parameter space and the phenomenology of charged Higgs decays?
• RQ4 Can bosonic-associated $H^+W^-$ production provide a viable discovery channel despite large $t\bar{t}$ backgrounds?
• RQ5 What are the upper bounds on $\tan\beta$ and $M_{H^\pm}$ consistent with theoretical and experimental constraints?

Key findings

• The $R_{\gamma\gamma}$ constraint from ATLAS (2-σ range: 1.05 to 2.33) significantly restricts the allowed parameter space, excluding values below unity.
• The $R_{VV}$ constraint (2-σ range: 0.3 to 2.7) from combined $WW$ and $ZZ$ channels further tightens limits on couplings of heavier Higgs states.
• A benchmark point $P'_{5}$ with $M_{H^\pm} \sim 600$ GeV and $M_{H_2} \sim M_{H^\pm} + M_W$ yields a favorable production cross section and decay rate for charged Higgs searches.
• Large $\tan\beta$ values are constrained by $B \to \tau\nu$ decays and theoretical bounds, with a cut-off around $\tan\beta \sim 5$–7 for $\mu = 0$.
• The requirement of a global minimum in the potential is computationally expensive and applied only after all other constraints are satisfied.
• Despite shrinking parameter space, the $H^+W^-$ channel remains a viable discovery channel due to effective suppression of $t\bar{t}$ backgrounds via kinematic cuts.