Direct searches for dark matter which targeted SUSY-motivated areas of parameter space employed well-studied nucleon interactions at keV to MeV energy scales to predict typical DM-nucleon interaction distributions. Much lighter DM, probed by a new generation of experiments sensitive to eV-scale energy deposits, however, rely instead on condensed matter effects to extract larger recoil energies from the DM than would be suggested by the simple elastic kinematics of heavier DM. In light of a growing number of unexplained low-energy excesses in these low-threshold experiments which appear to correlate with the degree of structure in the target material, we have begun to explore the role of inelastic scattering in DM-nucleon interactions, and are finding a similar effect in the DM-nucleon system as that seen in the DM-electron system arising from crystal structure. In this talk, I will discuss our recent progress in understanding the role of plasmon and multi-phonon excitations in DM-nucleon scattering and its implications for MeV-scale DM searches. I will also discuss some upcoming results which promise to shine more light on some of these processes and the near-term future of MeV-scale DM searches.
Zoom:https://yale.zoom.us/j/93903961284?pwd=empxRWhzdkY5SXpuQ2U2NmR1aWlpZz09