to the rho parameter is calculated as $$\begin{aligned}
  \Delta \rho_{Dt}^{} &= -
 \frac{N_c}{16\pi^2}\left(\frac{m_t^2}{\Lambda^2}\right)
 \left[
 \frac{\sqrt{2} m_t}{v}C_{Dt}^{}
  \left\{
  1 - \ln \frac{\Lambda^2+m_t^2}{m_t^2} - \frac{m_t^2}{\Lambda^2 +m_t^2}
 \right\}  \right.
 \nonumber \\
& \left. +C_{Dt}^2 \left\{
 1+ \frac{m_t^2}{\Lambda^2} \left( 1 - 2 \ln
 \frac{\Lambda^2+m_t^2}{m_t^2} 
 \right)
 - \frac{m_t^2}{\Lambda^2}\frac{m_t^2}{\Lambda^2+m_t^2}
 \right\}
 \right]. \label{eq:rho-dt}\end{aligned}$$ When $\Lambda=1$TeV, this can give a positive contribution only for $0 {\mbox{ \raisebox{-1.0ex}{$\stackrel{\textstyle <}
{\textstyle \sim}$ }}}C_{Dt}^{} {\mbox{ \raisebox{-1.0ex}{$\stackrel{\textstyle <}
{\textstyle \sim}$ }}}3$, and its maximal value is $\Delta\rho_{Dt}^{} \simeq +0.001$ at $C_{Dt} \sim 1.5$. This fact affects the allowed region of the Higgs boson mass. For a Higgs boson mass to be 500GeV, $C_{Dt}$ is only allowed to be around $+1.5$, where excessive negative (logarithmic) contribution of the Higgs boson to the rho parameter is approximately canceled by $\Delta\rho_{Dt}^{}$. In the following sections, we discuss the production cross section of $e^-e^+\to \nu\bar \nu t \bar t$ and that of its subprocess $W^+W^- \to t \bar t$. The mass of the Higgs boson is considered typically to be 500 GeV there, so that $C_{Dt}$ is necessarily constrained to be around +1.5 under the rho parameter result. Nevertheless some results will be shown for wider range of values of $C_{Dt}^{}$ only under the perturbative unitarity 