10 20 30 40 50 60 70 M(jj) [GeV] 0.1 0.2 0.3 0.4 Diff. cross section [fb/GeV] Signal BG Ma model W$^{+}$W 2j   + missing energy s=500 GeV jj m  = 100 GeV 0 100 200 300 400 500 M(jjjj) [GeV] 0.05 0.1 Diff. cross section [fb/GeV] Signal BG Ma model tt WW 4j+ missing energy s=500 GeV m  = 150 GeV FIG. 3: The jets invariant mass distributions of the production rates of the signal in the Ma model at √ s = 500 GeV. left : The di-jet invariant mass M ( jj ) distribution of the signal e $^{+}$e − → ξ $^{+}$ξ − → jjµνξ 0 $_{r}$ξ 0 r for m$_{ξ}$ ± = 100 GeV. right : M ( jjjj ) distribution of e $^{+}$e − → ξ $^{+}$ξ − → W $^{+}$W $^{−}$ξ 0 $_{r}$ξ 0 r → jjjjξ 0 r for m$_{ξ}$ ± = 150 GeV. In addition to the rate from the signal process, those for main backgrounds are also shown. At current and future LFV experiments, the coupling constants f$_{ij}$ and g$_{ij}$ can be further tested via the LFV rare decays such as ℓ → ℓ $^{′}$γ and ℓ → ℓ $^{′}$ℓ$^{′}$ℓ$^{′′}$. The same operators as in ℓ − → ℓ $^{′∓}$e$^{−}$e± would also be tested directly at the ILC via e $^{±}$e− → ℓ $^{−}$ℓ $^{$^{′}$±}$. In the scenario in Eq. (11), we estimate that σ ( e $^{+}$e − → µ $^{±}$τ $^{∓}$) ∼ 5 fb for √$_{s}$ = 1 TeV. When we take g$_{ee}$ = 0 . 4, g$_{eτ}$ = 0 . 01, m$_{k}$ = µ = 1 . 2 TeV and m$_{ω}$ = 400 GeV, which also satisfy all the current data, we obtain σ ( e $^{+}$e − → τ $^{±}$e$^{∓}$) ∼ 0 . 76 (1.7) fb for √$_{s}$ = 500 GeV (1 TeV). In the Ma model, the coupling constants ˆ h α e ( α = 1 , 2) 7 are strongly constrained from neutrino data and LFV data. As a typical choice of parameters, we consider 8 in which the normal neutrino mass hierarchy is realized. Because ˆ h α e are very small for a 7 Here we consider the minimal case of two generations for the right-handed neutrino. 8 The relatively large mass difference between ξ ± and ξ 0 r,i implies a significant deviation from the custodial symmetry in the Higgs sector, which affects the allowed mass m$_{h}$ of the SM like Higgs boson h . The larger m$_{h}$ is favored for larger mass difference of m$_{ξ}$ ± − m$_{ξ}$$_{r,i}$ . 12 m$_{ξ}$$_{r}$ = 50 GeV , m$_{ξ}$$_{i}$ = 60 GeV , m$_{ξ}$ ± ∼ 100 GeV , m$_{N}$ 1 R = m$_{N}$ 2 R = 3 TeV , λ$_{5}$ = − 1 . 8 × 10 − $^{2}$, ˆ h α e , ˆ h α $_{µ}$, ˆ h α τ ∼ 10 − $^{5}$, (12) The Ma model