method of the EWA[@ewa] by using the result of calculation of the subprocess. We also show the results of full matrix-element calculation based on CalcHEP[@calchep] and LanHEP[@lanhep], and compare the both results. As we show soon later, the EWA gives reasonable results for a large value of $\sqrt{\hat{s}}$ as compared to $m_W^{}$. In order to keep the validity of the calculation based on the EWA, we need to make the kinematic cut at an appropriate value. Here we employ the cut $M_{tt}^{}>400$ GeV[@godfrey]. The accuracy of the EWA has been discussed by many authors[@Johnson:1987tj; @nagashima]. Our results agree with those in Ref. [@larios] where expected error is evaluated to be of the order of 10% for the cut $M_{tt}^{}>500$ GeV.

In Fig. \[fig:SigmaCut400-SM\], the SM results for the cross section of $e^-e^+\to W^-_\lambda W^+_{\bar \lambda} \nu \bar \nu \to t \bar t \nu
  \bar \nu$ are shown as a function of $m_H^{}$ with the kinematic cut $M_{tt} \ge 400$ GeV. The electron-positron collider energy $\sqrt{s}$ is set to be 1 TeV. This is a reproduction of the results in Refs. [@godfrey; @godfrey2] For a heavy Higgs boson ($m_H^{} > 2 m_t$) the longitudinally polarized mode ($LL$) is dominant due to 