Light charged Higgs bosons to AW/HW via top decay

While current ATLAS and CMS measurements exclude a light charged Higgs (m(H +/-) < 160 GeV) for most of the parameter region in the context of the MSSM scenarios, these bounds are significantly weakened in the Type II 2HDM once the exotic decay channel into a lighter neutral Higgs, H-+/- -> AW/HW, is open. In this study, we examine the possibility of a light charged Higgs produced in top decay via single top or top pair production, which is the most prominent production channel for a light charged Higgs at the LHC. We consider the subsequent decay H-+/- -> AW/HW, which can reach a sizable branching fraction at low tan beta once it is kinematically permitted. With a detailed collider analysis, we obtain exclusion and discovery bounds for the 14TeV LHC assuming the existence of a 70 GeV neutral scalar. Assuming BR(H-+/- -> AW/HW) = 100% and BR(A/H -> tau tau) = 8.6%, the 95% exclusion limits on BR(t -> H(+)b) are about 0.2% and 0.03% for single top and top pair production respectively, with an integrated luminosity of 300 fb(-1). The discovery reaches are about 3 times higher. In the context of the Type II 2HDM, discovery is possible at both large tan beta > 17 for 155 GeV < m(H +/-) < 165 GeV, and small tan beta < 6 over the entire mass range. Exclusion is possible in the entire tan beta versus m(H +/-) plane except for charged Higgs masses close to the top threshold. The exotic decay channel H-+/- -> AW/HW is therefore complementary to the conventional H-+/- -> tau nu channel.