Higgs Signals in a Type I 2HDM or with a Sister Higgs

TL;DR

The paper investigates how adding a non-fermion-coupled Higgs doublet (Type I 2HDM or a SUSY sister-Higgs sector) can modify Higgs couplings to explain potential deviations at $m_h\approx125$ GeV. It shows that near the SM-like point, $c_V=\\cos\\delta\\approx1$ while $c_f=\\cos\\delta-\\cot\\beta\\sin\\delta$ can be suppressed, yielding enhanced $h\to\gamma\gamma$ in VBF and somewhat SM-like $WW^*/ZZ^*$ with reduced $h\to\tau\tau$, plus possible loop contributions from light charged states. A parametric study reveals that, after flavor and EW constraints, inclusive $\gamma\gamma$ signals can rise by up to ~50% and VBF/associated signals by ~60% over SM expectations, with a diphoton width shift $\\delta c_{\\gamma\\gamma}$ up to ~0.14; a light charged Higgs is commonly predicted. In SUSY realizations, sister-Higgs multiplets and G-quarks can further enhance $\\Gamma_{\\gamma\gamma}$ and provide additional collider signatures, offering a cohesive framework to interpret early Higgs data while remaining consistent with precision constraints.

Abstract

In models where an additional SU(2)-doublet that does not have couplings to fermions participates in electroweak symmetry breaking, the properties of the Higgs boson are changed. At tree level, in the neighborhood of the SM-like range of parameter space, it is natural to have the coupling to vectors, cV, approximately constant, while the coupling to fermions, cf, is suppressed. This leads to enhanced VBF signals of gamma gamma while keeping other signals of Higgses approximately constant (such as WW* and ZZ*), and suppressing higgs to tau tau. Sizable tree-level effects are often accompanied by light charged Higgs states, which lead to important constraints from b to s gamma and top to b H+, but also often to similarly sizable contributions to the inclusive h to gamma gamma signal from radiative effects. In the simplest model, this is described by a Type I 2HDM, and in supersymmetry is naturally realized with "sister Higgs" fields. In such a scenario, additional light charged states can contribute further with fewer constraints from heavy flavor decays. With supersymmetry, Grand Unification motivates the inclusion of colored partner fields. These G-quarks may provide additional evidence for such a model.

Figures (4)

• Figure 1: $\sigma\times BR$, relative to the SM ($\delta=0$), for gluon fusion to $\gamma\gamma$ (dotted red), gluon fusion to $WW^*/ZZ^*$ (dashed green), VBF to $\gamma\gamma$ (solid blue), gluon fusion to $\tau\tau$ (dot-dashed brown), and VBF to $WW^*/ZZ^*$ (long-dashed gray). The horizontal lines are at the SM rate $\pm 20\%$. The lines ignore the contribution of new charged states to the $\gamma\gamma$ width. The bands show the effect of an additional charged state whose loop contribution is smaller in magnitude than 50% of the top contribution.
• Figure 2: Results of a scan as described in the text, with the gray points ($\square$) corresponding to values of $\tan\beta$ failing the the $b\rightarrow s\gamma$ constraint, the blue points ($\circ$) satisfying this bound (but $\tan\beta<3$), but failing constraints on $S$ and $T$, the green ($\triangledown$) satisfying all these bounds, but failing the additional constraint from $t\rightarrow b H^+$, and the purple ($\star$) passing all these constraints. The upper right hand plot ignores the effects on $\Gamma_{\gamma\gamma}$ of the charged Higgs running in the loop, while all other plots include it.
• Figure 3: The correction, $\delta c_{\gamma\gamma}$, to the diphoton width, $\Gamma_{\gamma\gamma}$, of the Higgs from the charged Higgs of the Type I 2HDM. The color scheme is as in Figure \ref{['fig:scans']}.
• Figure 4: Distribution of heavy higgs masses in scan. The gray applies all constraints, including perturbativity ($|\lambda|<2$) vacuum stability (\ref{['eq:vacstability']}), the constraints from $S$, $T$, $t \rightarrow b H^+$ and $b \rightarrow s \gamma$. The green has an additional requirement of $R_{VBF}(\gamma \gamma)>1.3$.