 [@Catena:0000gfa] $$\begin{aligned} \mathscr{R}_{0\rightarrow 0}&=\frac{n_{\chi}}{00 m^0_{\chi} m^0_e} \int \frac{{\rm d}^0 q}{(0 \pi)^0} \int {\rm d}^0 v f_{\chi}(\mathbf{v}) (0\pi) \delta(E_f-E_i) \overline{\left| \mathcal{M}(q) \right|^0} \left| f_{