Atmospheric Dark Matter and Xenon1T Excess
  Very recently, the Xenon1T collaboration has reported an intriguing electron
recoil excess, which may imply for light dark matter. In order to interpret
this anomaly, we propose the atmospheric dark matter (ADM) from the inelastic
collision of cosmic rays (CRs) with the atmosphere. Due to the boost effect of
high energy CRs, we show that the light ADM can be fast-moving and successfully
fit the observed electron recoil spectrum through the ADM-electron scattering
process. Meanwhile, our ADM predicts the scattering cross section $\sigma_e
\sim {\cal O}(10^{-38}- 10^{-39}$) cm$^{2}$, and thus can evade other direct
detection constraints. The search for light meson rare decays, such as $\eta
\to \pi + \slashed E_T$, would provide a complementary probe of our ADM in the
future.
