Direct Detection of Sub-GeV Dark Matter
  Direct detection strategies are proposed for dark matter particles with MeV
to GeV mass. In this largely unexplored mass range, dark matter scattering with
electrons can cause single-electron ionization signals, which are detectable
with current technology. Ultraviolet photons, individual ions, and heat are
interesting alternative signals. Focusing on ionization, we calculate the
expected dark matter scattering rates and estimate the sensitivity of possible
experiments. Backgrounds that may be relevant are discussed. Theoretically
interesting models can be probed with existing technologies, and may even be
within reach using ongoing direct detection experiments. Significant
improvements in sensitivity should be possible with dedicated experiments,
opening up a window to new regions in dark matter parameter space.
