Electronic structure approach to compute Dark Matter-Electron scattering cross-sections in Direct Detection experiments

The existence of dark matter in the Universe is nowadays overwhelming. Numerous direct detection experiments are currently on going or planned all around the world. As the mass of these dark matter particles is unknown, these experiments explore different mass ranges, with a large majority being sensitive to masses above the GeV range. In these experiments dark matter is assumed to scatter from the nuclei and background models are built upon a combined theoretical and experimental characterization of nuclear recoils in the detectors. Recently, however, dark matter in the sub-GeV mass range has received much attention, and several well-motivated theoretical models exist for candidates in this mass range. The traditional method of detecting the nuclear recoil does not apply for sub-GeV dark matter because the recoil energy falls below the detector threshold. However, the scattering of dark matter with atomic electrons can produce observable ionization signals. In this talk we present the theoretical model to estimate the dark matter-electron scattering event rate using first principle methods. We will show how this rate estimation depends on the underlying theoretical approximations. We also show results for different systems like liquid Xe, Si and Ge.