Light A physics in the lepton-specific two-Higgs doublet model

We examine various direct and indirect constraints on the lepton-specific two-Higgs doublet model and discuss its phenomenology at colliders in the allowed parameter space. The constraints we consider come from the precision electroweak data, the direct search for Higgs boson, the muon anomalous magnetic moment, as well as some theoretical consistency requirements. We find that in the allowed parameter space the CP-odd Higgs boson A is rather light (m (A) < 30 GeV with 95% possibility), which is composed dominantly by the leptonic Higgs and decays dominantly into tau (+) tau (-); while the SM-like Higgs boson h (responsible largely for electroweak symmetry breaking) decays dominantly in the mode h -> AA -> 4 tau with a large decay width, which will make the Higgs discovery more difficult at the LHC. Whereas, this scenario predicts rare Z decays Z -> AAA and Z -> tau (+) tau (-) A with their branching ratios ranging from 10(-8) to 10(-3) and 10(-5) to 10(-4) respectively, which may be accessible at the GigaZ option of the ILC.