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 b (b) over bar 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 beta, m(H +/-), and CP-odd Higgs doublet component. We discuss search strategies based on A -> tau(+)tau(-) with both taus decaying leptonically, and on the subleading decay mode A -> mu(+)mu(-). We show that a search for t -> H(+)b, H+ -> W(+)A, A -> mu(+)mu(-) 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.