Lepton-specific two-Higgs-doublet model: Experimental constraints and implication on Higgs phenomenology

We examine various direct and indirect constraints on the lepton-specific two-Higgs-doublet model and scrutinize the property of the Higgs bosons in the allowed parameter space. We find that in the allowed parameter space the $CP$-odd Higgs boson A is rather light (mA<30 GeV with 95% possibility), which is composed dominantly by the leptonic Higgs and decays dominantly into τ⁺τ^-; while the standard-model-like Higgs boson h (responsible largely for electroweak symmetry breaking) decays dominantly in the mode h→AA→4τ with a large decay width, which will make the Higgs discovery more difficult at the LHC, whereas this scenario predicts a branching ratio Br(Z→τ⁺τ^-A) ranging from 10^-5 to 10^-4, which may be accessible at the GigaZ option of the International Linear Collider.