Direct Detection of Dark Matter Bound to the Earth
  We study the properties and direct detection prospects of an as of yet
neglected population of dark matter (DM) particles moving in orbits
gravitationally bound to the Earth. This DM population is expected to form via
scattering by nuclei in the Earth's interior. We compute fluxes and nuclear
recoil energy spectra expected at direct detection experiments for the new DM
population considering detectors with and without directional sensitivity, and
different types of target materials and DM-nucleon interactions. DM particles
bound to the Earth manifest as a prominent rise in the low-energy part of the
observed nuclear recoil energy spectrum. Ultra-low threshold energies of about
1 eV are needed to resolve this effect. Its shape is independent of the
DM-nucleus scattering cross-section normalisation.
