Trilepton signatures of light charged and CP-odd Higgs bosons in top quark decays

In singlet extensions of the two Higgs doublet model, a light CP-odd Higgs boson (A) can significantly modify decay modes of the charged Higgs, without necessarily affecting decay modes of the standard model-like Higgs boson. These effects can be sizable even if the doublet component of the light CP-odd Higgs is small, so that constraints from Upsilon decays and direct CP-odd Higgs production do not apply. We study a scenario in which the charged Higgs is produced in top quark decays, t → H±b, with dominant H± → W±A. We focus on the CP-odd Higgs mass range below the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$ b\overline{b} $\end{document} threshold. We summarize all current experimental constraints and find that, as a result of H± → W±A dominance, this scenario is not constrained in a large region of tan β, mH± , and CP-odd Higgs doublet component. We discuss search strategies based on A → τ+τ−, with both taus decaying leptonically, and on the subleading decay mode A → μ+μ−. We show that a search for t → H+b, H+ → W+A, A → μ+μ− in 20 fb−1 of 8 TeV LHC data can constrain most of the currently allowed parameter space. Existing trilepton searches are not sensitive to this signal due to the adopted isolation criteria.