The possibility of a light charged Higgs boson $H^{\pm }$ that decays predominantly to a charm quark and a bottom quark ($cb$) and with a mass in the range $80\mathrm{GeV}\le M_{H^{\pm }}\le 90\mathrm{GeV}$ is studied in the context of a three-Higgs doublet model (3HDM). Searches for this decay at the Large Hadron Collider do not have sensitivity to this mass region at present. It is shown that the searches for $H^{\pm }$ at LEP2 could be supplemented by either one or two $b$-tags, which would enable such large branching ratios for $H^{\pm }\to cb$ to be probed in the above mass region. We comment on the possibility of this 3HDM scenario to explain a slight excess in the searches for $H^{\pm }$ at LEP2, which is best fit by $M_{H^{\pm }}$ of around 90 GeV, and discuss the prospects for detecting $H^{\pm }\to cb$ decays at future $e^{+}{e}^{-}$ colliders.

• Received 21 August 2019
• Accepted 27 January 2020

DOI:https://doi.org/10.1103/PhysRevD.101.035021

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Published by the American Physical Society