Multi-tau lepton signatures in leptophilic two Higgs doublet model at the ILC

We study the feasibility of the Type-X two Higgs doublet model (THDM-X) at collider experiments. In the THDM-X, new Higgs bosons mostly decay into tau leptons in the wide range of the parameter space. Such scalar bosons are less constrained by current experimental data, because of the suppressed quark Yukawa interactions. We discuss a search strategy of the THDM-X with multi-tau lepton final states at International linear collider and Large Hadron Collider. By using the collinear approximation, we show that a four tau lepton signature (e^+e^- -> HA -> 4tau) can be a clean signal.