A Dark Matter Interpretation of Excesses in Multiple Direct Detection
  Experiments
  We present a novel unifying interpretation of excess event rates observed in
several dark matter direct-detection experiments that utilize single-electron
threshold semiconductor detectors. Despite their different locations,
exposures, readout techniques, detector composition, and operating depths,
these experiments all observe statistically significant excess event rates of
$\sim$ 10 Hz/kg. However, none of these persistent excesses has yet been
reported as a dark matter signal because individually, each can be attributed
to different well-motivated but unmodeled backgrounds, and taken together, they
cannot be explained by dark matter particles scattering elastically off
detector nuclei or electrons. We show that these results can be reconciled if
the semiconductor detectors are seeing a collective inelastic process,
consistent with exciting a plasmon. We further show that plasmon excitation
could arise in two compelling dark matter scenarios, both of which can explain
rates of existing signal excesses in germanium and, at least at the order of
magnitude level, across several single-electron threshold detectors. At least
one of these scenarios also yields the correct relic density from thermal
freeze-out. Both dark matter scenarios motivate a radical rethinking of the
standard interpretations of dark matter-electron scattering from recent
experiments.
