Cutting rules for non-relativistic dark matter in solids based on Kohn-Sham orbitals

The Cutkosky cutting rules establish a direct connection between the imaginary parts of loop amplitudes and physical observables such as decay rates and cross sections, providing heuristic insights into the underlying processes. This work lays a robust theoretical foundation for the application of cutting rules in solid-state systems involving instantaneous dark matter (DM)–electron Yukawa interaction as well as the Coulomb potential. The cutting rules are formulated using the single-electron wavefunctions and corresponding energy eigenvalues obtained from the Kohn-Sham equations within density functional theory (DFT). This framework is not only of considerable theoretical interest but also holds significant practical relevance for studying DM phenomenology in condensed matter systems.