Only consider the interaction term between electron Higgs and $Z$ boson $$ \mathcal{L}_{h ff}=-\frac{Y_f v}{\sqrt{2}} \bar{\psi} \psi\left(1+\frac{h}{v}\right) =-m_f \bar{\psi} \psi\left(1+\frac{h}{v}\right) $$ $$ \mathcal{L}_{Z}=\frac{e}{2\sin\theta_W\cos\theta_W}\bar{\psi}\gamma^\mu \left(g_{\mathrm{V}}-g_{\mathrm{A}}\gamma^5\right)\psi Z_{\mu}. $$
Then we consider the process $e^{-}+h\rightarrow e^{-}+Z$, there're only two diagrams, one is $t$-channel:
the other is $s$-channel
While in the first diagram $t$-channel, if we choose the momentum of electron in center-of-mass frame larger than 30GeV, the propagator would be divergence in a specific direction, ie. the virtual positron could be on-shell, $t$-channel diagram is equivalent to two process $e^{-}+e^{+}\rightarrow Z$ and $h\rightarrow e^{-}+e^{+}$.
So how to calculate the cross section of this process? especially for differential cross section？
There're many similar processes such as $\nu_{e}+h\rightarrow e^{-}+W^{+}\rightarrow e^{-}+\mu^{+}+\nu_{\mu}$
