Differential Cross-Section

[math]-i \mathfrak{M}_{e^-e^-}=-i \left ( \frac{e^2(p_A+p_C)_{\mu}(p_B+p_D)^{\mu}}{(p_D-p_B)^2}- \frac{e^2(p_A+p_D)_{\mu}(p_B+p_C)^{\mu}}{(p_C-p_B)^2} \right )[/math]

[math] \mathfrak{M}_{e^-e^-}= e^2\left ( \frac{(p_Ap_B+p_Cp_D+p_Cp_B+p_Ap_D}{(p_D-p_B)^2}- \frac{(p_Ap_B+p_Dp_C+p_Dp_B+p_Ap_C}{(p_C-p_B)^2} \right )[/math]

[math]\mathfrak{M}_{e^-e^-}=e^2 \left (\frac{u-s}{t}+\frac{t-s}{u} \right )[/math]