Comprehensive study of the light charged Higgs boson in the type-I two-Higgs-doublet model

In the type-1 two-Higgs-doublet model, existing theoretical and experimental constraints still permit a light charged Higgs boson with a mass below the top quark mass. We present a complete road map for the light charged Higgs boson at the LHC through a comprehensive phenomenology study, focusing on the normal scenario where the lighter CP-even Higgs boson is the observed Higgs boson. In type I, it is challenging to simultaneously accommodate the light mass of the charged Higgs boson and the constraints from theoretical stabilities, electroweak precision data, Higgs data, b -> s gamma, and direct search bounds. Consequently, the parameter space is extremely curtailed, which predicts somewhat definite phenomenological signatures. We find that the mass of the pseudoscalar Higgs boson, M-A, is the most crucial factor in the phenomenology of the charged Higgs boson. If M-A is light, the charged Higgs boson decays mainly into AW(+/-). When M-A is above the AW(+/-) threshold, the dominant decay mode is into tau(+/-)nu. Over the entire viable parameter space, we study all the possible production and decay modes of charged Higgs bosons at the LHC and suggest three efficient channels: (i) p p -> H+ H- -> [tau nu][tau nu], (ii) pp -> HA/HH/AA -> (HWHW -/+)-W-+/--H--/+-W-+/- -> [tau nu][tau nu]WW, and (iii) pp -> H+ H- -> [b (b) over bar][b (b) over barW]. Based on sophisticated signal-background analyses including detector simulation, we show that the significance of the first final state is large and that of the second one is marginal (around 3), but that the third one suffers from enormous t (t) over bar related backgrounds.