Discriminating leptonic Yukawa interactions with doubly charged scalar at the ILC

We explore discrimination of two types of leptonic Yukawa interactions associated with Higgs triplet, $\bar L^c_L \Delta L_L$, and with $SU(2)$ singlet doubly charged scalar, $\bar e_R^c k^{++} e_R$. These interactions can be distinguished by measuring the effects of doubly charged scalar boson exchange in the $e^+ e^- \to \ell^+ ell^-$ processes at polarized electron-positron colliders. We study a forward-backward asymmetry of scattering angular distribution to estimate the sensitivity for these effects at the ILC. In addition, we investigate prospects of upper bounds on the Yukawa couplings by combining the constraints of lepton flavor violation processes and the $e^+ e^- \to \ell^+ \ell^-$ processes at the LEP and the ILC.