  We propose boosted dark matter (BDM) as a possible explanation for the excess
of keV electron recoil events observed by XENON1T. BDM particles have
velocities much larger than those typical of virialized dark matter, and, as
such, BDM-electron scattering can naturally produce keV electron recoils. We
show that the required BDM-electron scattering cross sections can be easily
realized in a simple model with a heavy vector mediator. Though these cross
sections are too large for BDM to escape from the Sun, the BDM flux can
originate from the Galactic Center or from halo dark matter annihilations.
Furthermore, a daily modulation of the BDM signal will be present, which could
not only be used to differentiate it from various backgrounds, but would also
provide important directional information for the BDM flux.
