Abstract
The scenario of two mass-degenerate Higgs bosons within the general two-Higgs-doublet model (2HDM) is revisited. We focus on the global picture when two $CP$-even Higgs bosons of $h$ and $H$ are nearly mass-degenerate. A global fit to the signal strength of the 125 GeV Higgs measured at the LHC is performed. Based on the best-fit result of the 2HDM mixing angles $(\alpha,\beta)$, theoretical constraints, charged and $CP$-odd Higgs boson direct search constraints and the electroweak precision constraints are imposed to the 2HDM parameter space. We present the signal predictions of the $(4b\,, 2b\,2\gamma)$ channels for the benchmark models at the LHC 14 TeV runs. We also study the direct Higgs boson pair productions at the LHC, and the Z-associated Higgs boson pair production search at the ILC 500 GeV runs, as well as the indirect probes at the CEPC 250 GeV run. We find that the mass-degenerate Higgs boson scenario in the Type-II 2HDM can be fully probed by these future experimental searches.
Highlights
When the 125 GeV Higgs boson was discovered at the LHC 7 ⊕ 8 TeV runs [1,2], the experimental measurements of the γγ signal rates from both ATLAS and CMS collaborations were both enhanced relative to the standard model (SM) predictions
We show the indication from the precise measurement of cross sections of mass-degenerate Higgs bosons with Z-boson for this scenario at the circular electron-positron colplidffiffier (CEPC)
For the fixed heavy Higgs boson masses of MA 1⁄4 MÆ in the Type-I case, a smaller m12 leads to a relatively larger positive λ1. This results in a larger jaþj, which in turn gives the lower bounds on m12 on the left panel of Fig. 2
Summary
When the 125 GeV Higgs boson was discovered at the LHC 7 ⊕ 8 TeV runs [1,2], the experimental measurements of the γγ signal rates from both ATLAS and CMS collaborations were both enhanced relative to the standard model (SM) predictions. We suggest to distinguish the h=H mass-degenerate case from the single resonance case through the probes of the Higgs boson self couplings This can be done by searching for the Higgs boson pair production processes at both LHC and the future high-energy colliders.
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