$Z$ boson mediation and the $b$-quark mediation are respectively given by $$\begin{aligned}
&{\mathcal M}_H^{WW\to t\bar{t}} \times
 (2\pi)^3\sqrt{2p^0}\sqrt{2{p'}^0} 
=\frac{(2 m_W^2/v)}
{\hat{s}-m_H^2+i m_H^{} \Gamma_H^{}}
 \frac{y_t^{\rm eff}(\hat{s},\Lambda)}{\sqrt{2}}
(\epsilon_\lambda \cdot {\epsilon'}_{\bar \lambda}) \bar{u}_t v_t, \label{h-med}\\
&{\mathcal M}_Z^{WW\to t\bar{t}} 
\times (2\pi)^3\sqrt{2p^0}\sqrt{2{p'}^0}=
- \frac{2 m_W^2/v^2}{\hat{s}-m_Z^2} 
A^\mu_{\lambda \bar \lambda} \bar{u}_t \left[ i \gamma_\mu 
(V_t+A_t \gamma_5) + \frac{C_{Dt}}{\Lambda^2} 
\frac{v}{2\sqrt{2}} K_\mu \right]v_t,  \\
&{\mathcal M}_b^{WW\to t\bar{t}} 
\times (2\pi)^3\sqrt{2p^0}\sqrt{2{p'}^0}&  \nonumber \\
 & \hspace*{+1cm}
=-\frac{2m_W^2/v^2}{\hat{u}-m_b^2} 
\epsilon_\lambda^\mu {\epsilon'}_{\bar \lambda}^\nu \bar{u}_t \left[
\left(i \gamma_\nu + \frac{C_{Dt}}{\sqrt{2}} \frac{v}{\Lambda^2}
k_\nu \right)
 P_L i \gamma_\rho (p-k')^\rho
 \left( i \gamma_\mu - \frac{C_{Dt}}{\sqrt{2}}
 \frac{v}{\Lambda^2}
 {k}'_\mu \right) \right] v_t,  \end{aligned}$$ where $\epsilon=\epsilon(p,\lambda)$ and $\epsilon'=\epsilon(p',\bar\lambda)$; $\bar u_t$ ($v_t$) is the Dirac spinor for outgoing $t$ ($\bar t$); $p$ ($p'$) and $k$ ($k'$) are the momenta of the incoming $W^-$ ($W^+$) and outgoing $t$ ($\bar t$); $q=p+p'$, $P=p-p'$, $K=k-k'$, $P_{L}^{}=(1 + \gamma_5)/2$, $A_t=\frac{1}{2}$, $V_t=\frac{1}{2}-2 Q_t \sin^2\theta_W$ with $\theta_W^{}$ being the Weinberg angle; and $A_{\lambda\bar\lambda}^\mu = (\epsilon_\lambda \cdot
  {\epsilon'}_{\bar \lambda})P^\mu
  + 2 (\epsilon_\lambda \cdot q){\epsilon'}_{\bar \lambda}^\mu
  - 2({\epsilon'}_{\bar \lambda} \cdot q) \epsilon_\lambda^\mu $. Mandelstam variables[^2] are defined by $\hat{s}=-q^2$, $\hat{t}=-(p-k)^2=-(p'-k')^2$ and $\hat{u}=-(p-k')^2=-(p'-k)^2$. The diagram of the photon mediation is not changed by the existence of the operators ${\cal O}_{t1}$ and ${\cal O}_{Dt}^{}\,$; $$\begin{aligned}
{\mathcal M}_\gamma^{WW\to t\bar{t}} 
\times (2\pi)^3\sqrt{2p^0}\sqrt{2{p'}^0}=& 
- \frac{Q_t e^2}{\hat{s}} A^\mu_{\lambda 