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

TL;DR

This paper explores the scenario where two nearly mass-degenerate Higgs bosons exist in the two-Higgs-doublet model, analyzing their detectability through various collider experiments and providing predictions for future searches.

Contribution

It provides a comprehensive analysis of the mass-degenerate Higgs scenario in the 2HDM, including global fits, theoretical and experimental constraints, and future collider search predictions.

Findings

Mass-degenerate Higgs scenario in Type-II 2HDM can be fully tested by future experiments.

Predicted signals for $(4b, 2b2\,\gamma)$ channels at LHC 14 TeV.

Studied Higgs pair production at LHC, ILC, and CEPC.

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.