[Paper Review] Two Higgs Doublet Model, Standard Model-like Scenario and Resolving SM from 2HDM at Photon Colliders

I. F. Ginzburg, M. V. Vychugin|ArXiv.org|Jan 14, 2002

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates a natural Two Higgs Doublet Model (2HDM) with suppressed CP violation and Flavor Changing Neutral Currents, showing that the Standard Model-like scenario—where no deviations from SM are found at LHC and $e^+e^-$ colliders—remains viable across a broad 2HDM parameter space. It demonstrates that photon collider processes $\gamma\gamma \to h$ and $e\gamma \to eh$ can distinguish this natural 2HDM from the SM, with significant deviations in two-photon widths detectable even at 1\sigma experimental precision.

ABSTRACT

1. Discussing 2HDM and Higgs potential, we find the parameters range giving naturally weak effects of CP violation and Flavor Changing Neutral Currents. Within this approach, the widely discussed decoupling limit with heavy $H^\pm$, $H$ and $A$ corresponds to an unnatural set of 2HDM parameters. 2. We define the SM--like scenario as that in which after LHC and e^+e^- LC operations no visible deviations from the minimal SM will be found. We find all the parameter ranges of 2HDM compatible with this scenario. 3. We show that the study of Higgs boson production at Photon Colliders (processes $γγ o h$ and $e γ o eh$) can help to distinguish minimal SM from 2HDM with natural set of parameters.

Motivation & Objective

• To identify a natural 2HDM parameter space where CP violation and FCNC effects are suppressed, avoiding the unnatural decoupling limit.
• To define and characterize the SM-like scenario in 2HDM, where no deviations from the SM are observed at LHC and $e^+e^-$ colliders.
• To assess the potential of photon collider experiments to distinguish natural 2HDM from the SM based on Higgs production in $\gamma\gamma$ and $e\gamma$ processes.
• To analyze the sensitivity of $\gamma\gamma \to h$ and $e\gamma \to eh$ cross sections to different 2HDM solutions, particularly those with natural Yukawa couplings.

Proposed method

• The study uses a general 2HDM Higgs potential with $Z_2$ symmetry to suppress CP violation and FCNC, allowing only small $(\phi_1,\phi_2)$ mixing via soft $Z_2$ breaking.
• It defines the SM-like scenario as the absence of observable deviations from SM predictions at high-energy colliders, and maps the allowed 2HDM parameter ranges under this condition.
• The analysis computes Higgs couplings $\chi_i^\phi$ relative to SM values, using the ratio $|\chi_{\gamma\gamma}|^2$ to quantify deviations in two-photon widths.
• It evaluates $\gamma\gamma \to h$ and $e\gamma \to eh$ cross sections in 2HDM, comparing them to SM predictions, with sensitivity analysis under anticipated 1$\sigma$ experimental bounds.
• Solutions are classified into types A and B based on fermion coupling patterns: A assumes $\chi_u = \chi_d = \chi_V = 1$, while B assumes $\chi_u + \chi_d \approx 0$, leading to distinct $\gamma\gamma$ width behaviors.
• The paper uses the relation $|\chi_{\gamma\gamma}|^2 = 1 - R_{\gamma\gamma}(1 - |\mu^2|/M_{H^\pm}^2)$ to model $H^\pm$ loop contributions, with $\mu \lesssim v$ for naturalness.

Experimental results

Research questions

• RQ1 Which 2HDM parameter ranges allow a natural suppression of CP violation and FCNC effects, avoiding the decoupling limit?
• RQ2 What are the viable 2HDM realizations consistent with a SM-like scenario, where no deviations from SM are observed at LHC and $e^+e^-$ colliders?
• RQ3 Can photon collider processes $\gamma\gamma \to h$ and $e\gamma \to eh$ distinguish a natural 2HDM from the SM, and at what sensitivity?
• RQ4 How do different 2HDM solutions (A and B) affect the two-photon Higgs width and $e\gamma \to eh$ cross section, and can they be distinguished experimentally?
• RQ5 To what extent can $H^\pm$ loop contributions modify Higgs couplings in 2HDM, and how does this affect the detectability of deviations from SM?

Key findings

• The natural 2HDM with small $(\phi_1,\phi_2)$ mixing and suppressed CP/FCNC effects corresponds to a broad parameter space distinct from the decoupling limit, which requires unnatural parameters.
• The SM-like scenario in 2HDM includes not only the decoupling limit but also multiple other realizations, including those with light charged Higgs bosons.
• The two-photon Higgs width in natural 2HDM can deviate significantly from the SM value—by up to 20% in solution $B_{h+u}$—making it detectable at photon colliders.
• For $M_h < 160$ GeV, the $e\gamma \to eh$ cross section provides substantial complementary sensitivity, especially in solution $B_{h+u}$, where it increases dramatically due to $t$-quark loop contributions.
• Solutions $B_{\phi\pm u}$ show clear deviations in $\gamma\gamma \to h$ width even under rough experimental measurements, independent of strong CP violation or FCNC effects.
• The paper finds no way to distinguish whether the observed Higgs is the lightest ($h_1$) or heaviest ($H$) state in the 2HDM spectrum using $\gamma\gamma$ or $e\gamma$ processes alone.