[Paper Review] Two-photon Higgs width and triple Higgs coupling in 2HDM at SM-like scenario

I. F. Ginzburg|arXiv (Cornell University)|May 8, 2015

Particle physics theoretical and experimental studies38 references3 citations

TL;DR

This paper investigates deviations in the two-photon Higgs decay width and the triple Higgs coupling within the Two-Higgs-Doublet Model (2HDM) under a Standard Model-like scenario. It shows that sizable deviations in both observables can arise simultaneously if the $H^+H^-h_1$ coupling is large, offering indirect evidence of new physics before direct charged Higgs discovery.

ABSTRACT

Within 2HDM, sizable deviations of the triple Higgs coupling and the two-photon Higgs width from their SM values can have a common origin. If SM-like scenario for the observed Higgs boson is realized, mentioned deviations can be either visible simultaneously or not observable at the LHC.}

Motivation & Objective

• To investigate whether sizable deviations in the two-photon Higgs width and triple Higgs coupling can coexist in the 2HDM under a SM-like scenario.
• To identify the conditions under which these deviations can be observed at the LHC despite the absence of direct charged Higgs boson detection.
• To explore the role of the $H^+H^-h_1$ vertex in generating observable effects in loop-induced Higgs decays and self-couplings.
• To assess the viability of detecting new physics effects through indirect signals when direct discovery of new Higgs states remains out of reach.
• To examine the impact of CP-violating effects and heavy neutral Higgs bosons on the observability of non-standard Higgs couplings.

Proposed method

• Uses relative couplings $\chi^P_a$ and $\chi^\pm_a$ to express deviations from SM predictions in Higgs couplings.
• Applies sum rules from the Higgs sector's unitarity and Hermiticity to constrain parameter space.
• Analyzes the two-photon decay width $\Gamma(h_1 \to \gamma\gamma)$ via loop contributions involving $H^\pm$ and CP-odd components.
• Evaluates the triple Higgs coupling $g(h_1h_1h_1)$ in terms of $\chi^\pm_1$, showing its sensitivity to $H^+H^-h_1$ vertex strength.
• Considers extreme parameter regimes such as $M_{2,3} \gtrsim \text{TeV}$ or $\chi^\pm_a \gtrsim 10$ to assess non-trivial effects.
• Performs numerical estimates with $\varepsilon_V^1 \approx 0.1$ to assess realistic deviations under moderate parameter settings.

Experimental results

Research questions

• RQ1 Under what conditions can both the two-photon Higgs width and the triple Higgs coupling deviate significantly from SM values in the 2HDM?
• RQ2 How is the $H^+H^-h_1$ coupling related to observable deviations in $\Gamma(h_1 \to \gamma\gamma)$ and $g(h_1h_1h_1)$?
• RQ3 Can large deviations in the triple Higgs coupling occur without large effects in the two-photon width, or are they necessarily correlated?
• RQ4 What role do heavy neutral Higgs bosons ($M_{2,3} \gtrsim \text{TeV}$) or strongly coupled $h_a H^+H^-$ vertices play in generating observable effects?
• RQ5 In the SM-like scenario with $\varepsilon_V \sim 0.1$, can indirect signals of new physics be detected before direct discovery of $H^\pm$?

Key findings

• Sizable deviations in both the two-photon Higgs width and the triple Higgs coupling from their SM values can coexist if the $H^+H^-h_1$ vertex is large, even at moderate $M_\pm$.
• A large $B_\pm \chi_1^\pm$ product (where $B_\pm \sim M_\pm^2/v$) leads to $|\chi(h_1h_1h_1) - 1| \gtrsim 1$, indicating a strongly modified triple Higgs coupling.
• Simultaneously, such a large $H^+H^-h_1$ coupling induces a significant deviation in $\Gamma(h_1 \to \gamma\gamma)$, making it a key indirect probe.
• Deviations in the triple Higgs coupling are unlikely under moderate parameters unless the $H^+H^-h_1$ coupling is enhanced or the $h_2, h_3$ states are very heavy ($> \text{TeV}$).
• For $M_2 \in (250, 400)$ GeV and $|\chi^t_2| > 1$, the $h_2$ state can be narrow and have a larger gluon fusion cross section than the SM Higgs, enabling resonant $gg \to h_2 \to h_1h_1$ production at the LHC.
• In the case of $\chi^\pm_a \gtrsim 10$, the two-photon width of $h_a$ would differ significantly from the SM prediction, even if $M_a$ is close to 125 GeV.