Narrow Trans-TeV Higgs Bosons and $H\to hh$ Decays: Two LHC Search Paths for a Hidden Sector Higgs Boson

TL;DR

This work studies a Standard Model extension where a hidden-sector singlet mixes with the SM Higgs via a renormalizable Higgs portal, producing two mass eigenstates $h$ and $H$ with a mixing angle $\omega$. The authors analyze theoretical constraints from perturbative unitarity, triviality, vacuum stability, and precision electroweak tests, and perform collider studies to show two primary LHC discovery paths: (i) a narrow trans-TeV Higgs resonance arising from reduced couplings and width, and (ii) decays of the heavier state via $H\to hh$, enabling dihiggs signatures such as $\gamma\gamma b\bar{b}$ and multi-lepton final states. They demonstrate that unitarity can accommodate a heavy $H$ with moderate to small mixing, and that dihiggs channels can provide early discovery potential alongside conventional searches, especially in the trans-TeV region. Overall, the paper argues that Higgs portal hidden-sector physics yields viable, distinct LHC signatures and motivates complementary search strategies to uncover such sectors.

Abstract

We consider the addition of a condensing singlet scalar field to the Standard Model. Such a scenario may be motivated by any number of theoretical ideas, including the common result in string-inspired model building of singlet scalar fields charged under some hidden sector gauge symmetry. For concreteness, we specify an example model of this type, and consider the relevant constraints on Higgs physics, such as triviality, perturbative unitarity and precision electroweak analysis. We then show that there are two unique features of the phenomenology that present opportunities for discovery at the Large Hadron Collider (LHC). First, it is possible to identify and discover a narrow trans-TeV Higgs boson in this scenario -- a mass scale that is well above the scale at which it is meaningful to discuss a SM Higgs boson. Second, the decays of the heavier scalar state into the lighter Higgs bosons can proceed at a high rate and may be the first discovery mode in the Higgs sector.

Figures (5)

• Figure 1: Scatter plot of solutions in the $m_H$ vs. $m_h$ plane that satisfies perturbative unitarity constraints. Separate colors are used depending on what range $s^2_\omega$ falls within.
• Figure 2: Scatter plot of solutions in the $m_H$ vs. $m_h$ plane that satisfies perturbative unitarity constraints. This plot is only for points that fall within $0.3<s^2_\omega < 0.4$.
• Figure 3: Differential cross-section as a function of the invariant mass of the $\ell$, ${E_T\!\!\!\!\!\!/\,\,\,}$ and two jets reconstructing to the $W$ mass for $H \rightarrow WW \rightarrow \ell\nu jj$ (solid), $WWjj$ (dashed), and $t\bar{t}jj$ (dotted).
• Figure 4: Differential cross-section as a function of transverse mass of the $Z$ and ${E_T\!\!\!\!\!\!/\,\,\,}$ for $H \rightarrow ZZ \rightarrow \ell\ell\nu\nu$ (solid) and the $ZZjj$ background (dashed).
• Figure 5: Differential cross-section as a function of invariant mass of $\gamma \gamma b \bar{b}$ for $H\rightarrow hh \rightarrow \gamma\gamma\bar{b} {b}$ (solid) and the sum of the backgrounds (dashed) requiring one $b$-tag.