\bar\lambda} 
\bar{u}_t i \gamma_\mu v_t.\end{aligned}$$

![ Feynman diagrams for the subprocess $\omega^-\omega^+ \to t \bar t$ in the model with the dimension-six operators ${\cal O}_{t1}$ and ${\cal O}_{Dt}$. []{data-label="fig:wwtt-sm"}](feynman-diagram-OmegaOmega-tt.eps){width="14cm"}

As seen from Eq. (\[h-med\]), the operator ${\cal O}_{t1}$ represents the shift of the SM top-Yukawa coupling, while ${\cal O}_{Dt}$ gives its momentum dependence. The effect of ${\cal O}_{Dt}$ enhances the effective Yukawa coupling as $\sqrt{\hat{s}}$ grows until the cutoff scale $\Lambda$. It turns out that this momentum dependence of the effective Yukawa coupling due to ${\cal O}_{Dt}$ in the Higgs boson mediation is replaced by the Higgs boson mass dependence due to the gauge cancellation mechanism. The invariant amplitude of the subprocess is obtained as $$\begin{aligned}
    {\cal M}^{WW\to tt} = 
{\cal M}^{WW\to tt}_H
+{\cal M}^{WW\to tt}_b
+{\cal M}^{WW\to tt}_Z
+{\cal M}^{WW\to tt}_\gamma. \end{aligned}$$

Calculation of the amplitude can be tested by using the equivalence of the longitudinally polarized weak boson ($W^\pm_L$) and the corresponding Nambu-Goldstone boson ($\omega^\pm$) for $\sqrt{\hat{s}} \gg m_W^{}$[@et]. In the Feynman gauge, the diagrams for the process $\omega^- \omega^+ \to t \bar t$ are shown in Fig. \[fig:wwtt-sm\], and each diagram is calculated as $$\begin{aligned}
{\mathcal M}_\times^{\omega^- \omega^+ \to t \bar t} 
(2 \pi)^3 \sqrt{2p^0} \sqrt{2{p'}^0} & 