the resonance of the Higgs boson in the Higgs boson mediated ($s$-channel) diagram, while for a relatively light Higgs boson all the modes $LL$, $LT$ and $TT$ are comparable. Therefore, information of the Yukawa interaction can more easily be extracted for heavier Higgs bosons.

Now we turn to the discussion on the case with the dimension-six operators ${\cal O}_{t1}$ and ${\cal O}_{Dt}$. In Figs. \[fig:SigmaCUT400-t1\](a) and \[fig:SigmaCUT400-t1\](b) cross sections for $e^- e^+ \to W^-_L W^+_L
 \nu \bar \nu \to  t \bar{t} \nu \bar{\nu}$ are shown as a function of $m_H^{}$ with the kinematic cut $M_{tt} \ge 400$ GeV. The collider energy is set to be $\sqrt{s}=1$ TeV. The new physics scale $\Lambda$ is assumed to be 1 TeV and 3 TeV. Fig. \[fig:SigmaCUT400-t1\](a) shows the results for Set B and Set C, and Fig. \[fig:SigmaCUT400-t1\](b) does those for Set D and Set E. In the both figures, the result in the SM case \[Set A\] is also plotted.

The cases for a higher collider energy ($\sqrt{s}=3$ TeV) are shown in Figs. \[fig:SigmaCUT400-Dt\](a) and \[fig:SigmaCUT400-Dt\](b). The new physics scale $\Lambda$ is assumed to be 3 TeV and 5 TeV. Fig. \[fig:SigmaCUT400-Dt\](a) shows the results for Set B and Set C, and 