(SM). Models of such new physics predict extended Higgs sectors with more than one scalar doublets in the low energy effective theory. These extended Higgs models would show distinctive features from the SM phenomenology. The most obvious evidence would be the confirmation of the existence of the extra scalar states such as CP-odd and charged states at future collider experiments. Even if they are too heavy to be directly discovered and only the lightest Higgs boson is found at the experiments, we would be able to explore the extended Higgs sector by searching for deviations from the SM predictions on the couplings with gauge bosons and fermions as well as on the self coupling. Furthermore, search for non-SM interactions can also be useful.

Lepton flavor violation (LFV) is an example for such non-SM phenomena. In particular, LFV in the Yukawa sector can only appear for extended Higgs sectors. Flavor violation between electrons and muons[@KunoOkada] has been tested through rare muon decays such as $\mu^{}\rightarrow e^{} \gamma$ and $\mu^{} \rightarrow e^{}e^{+}e^{-}$, as well as through $\mu$-$e$ conversion. Tau lepton associated LFV has also been studied by rare decays of tau leptons such as $\tau \rightarrow \ell_i P^0 $[@belle-tau-lp0], $\tau \rightarrow \ell_i 