Exploring the Higgs portal

TL;DR

The paper analyzes a Higgs portal linking the Standard Model to a hidden sector, yielding two mixed Higgs states H1 and H2 whose couplings and decays are governed by the mixing angle χ. It maps portal parameters to collider observables (M1,M2, κ_j, Γ^inv, Γ^{HH}_2) and defines twin-width ratios to quantify deviations from SM expectations, incorporating unitarity and S,T,U constraints. Through LHC-inspired profiling and visible/invisible channels, it identifies regions where one or both Higgs bosons can be discovered and outlines methods to extract χ and hidden-sector widths. With sufficient luminosity, the study shows that the underlying portal parameters {v_s, v_h, λ_s, λ_h, η_χ} and the Higgs self-coupling Λ_{211} can be reconstructed, providing a concrete path to characterize a hidden sector at the LHC.

Abstract

We study the Higgs portal from the Standard-Model to a hidden sector and examine which elements of the extended theory can be discovered and explored at the LHC. Our model includes two Higgs bosons covering parameter regions where the LHC will be sensitive to two, one or none of the particles at typical discovery luminosities for Standard Model Higgs production.

Figures (4)

• Figure 1: Left: masses of the light SM-like Higgs boson $H_1$ (blue) and the heavy Higgs boson $H_2$ (red). The parameters of the Higgs potentials are $v_h = v_s = 246$ GeV and $\lambda_s = \lambda_h /4 = 1/8$. The shaded region displays the LEP bound LEPred. Right: cascade decay width $\Gamma^{HH}_2$ as a function of $\sin^2\chi\,$ for the same parameters. Again, the region in which $H_1$ is excluded by LEP is shaded.
• Figure 2: Illustration of the intersections of the solutions for $\kappa_j$ (blue) and the invisible branching ratios (red), generating the physical solutions for the mixing parameter and the invisible widths. The Higgs portal model parameters are chosen $v_s=246~\text{GeV}$, $v_h=v_s$, $\lambda_s=1/8$ and $\lambda_h=4\lambda_s$; the intersection points of the curves correspond to the solution $\sin\chi =1/3$ for the mixing parameter.
• Figure 3: Randomly generated Higgs portal models. The parameters ranges are $v_h\in(0~\text{GeV},246~\text{GeV}], v_s= 246~\text{GeV}, \lambda_h\in(0,4\pi], \lambda_s\in(0,4\pi]$, and $\eta_\chi\in[-4\pi,4\pi]$. The hidden Higgs decay width we identify with the SM decay width, i.e. $\Gamma^\text{hid} \equiv \Gamma^\text{SM}$. LEP constraints and bounds from $S,T,U$Alcaraz:2006mx are included, likewise the unitarity constraint of Eq. (\ref{['eq:unitarity']}). Panel (a) displays the sensitivity for $H_1$ only, panel (b) for $H_2$ only, and panels (c) and (d) show where the LHC is sensitive to both $H_1$ and $H_2$ at the same time for $30~\text{fb}^{-1}$. Cross sections and widths we compute using Higluhiglu and Hdecayhdecay.
• Figure 4: (a) $\left\langle \sigma \text{BR}^\text{inv} \right\rangle$ corresponding to reference point #1. (cf. Tabs. \ref{['tab:sinex']} and \ref{['tab:lagextract']}). Both Higgs bosons exhibit significances of $3\sigma$ or more in the visible sector for ${\cal{L}}=30~\text{fb}^{-1}$ and will be well-established with ${\cal{L}}=300,~600~\text{fb}^{-1}$. The dotted line gives the true Monte Carlo value. (b) and (c) Extracting the mixing parameters in the reference points #2 and #3, respectively.