Future prospects of mass-degenerate Higgs bosons in the CP-conserving two-Higgs-doublet model

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, 2b2 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 massdegenerate Higgs boson scenario in the Type-II 2HDM can be fully probed by these future experimental searches.