In-medium screening effects for the Galactic halo and solar-reflected dark matter detection in semiconductor targets

Recently, the importance of the electronic many-body effect in the dark matter (DM) detection has been recognized, and a coherent formulation of the DM-electron scattering in terms of the dielectric response of the target material has been well established in literatures. In this paper, we put relevant formulas into practical density functional theory (DFT) estimation of the excitation event rates for the diamond and silicon semiconductor targets. Moreover, we compare the event rates calculated from the energy loss functions with and without the local field effects. For a consistency check of this numerical method, we also compare the differential spectrum and detection reach of the silicon target with those computed with the $\mathtt{GPAW}$ code. It turns out that these DFT approaches are quite consistent and robust. As an interesting extension, we also investigate the in-medium effect on the detection of the solar-reflected DM flux in silicon-based detectors, where the screening effect is found to be less remarkable than on detection of the Galactic DM, due to the high energies of the reflected DM particles.