Earth-bound Milli-charge Relics
  Dark sector particles with small electric charge, or millicharge, (mCPs) may
lead to a variety of diverse phenomena in particle physics, astrophysics and
cosmology. Assuming their possible existence, we investigate the accumulation
and propagation of mCPs in matter, specifically inside the Earth. Even small
values of millicharge lead to sizeable scattering cross sections on atoms,
resulting in complete thermalization, and as a consequence, considerable
build-up of number densities of mCPs, especially for the values of masses of
GeV and higher when the evaporation becomes inhibited. Enhancement of mCP
densities compared to their galactic abundance, that can be as big as
$10^{14}$, leads to the possibility of new experimental probes for this model.
The annihilation of pairs of mCPs will result in new signatures for the large
volume detectors (such as Super-Kamiokande). Formation of bound states of
negatively charged mCPs with nuclei can be observed by direct dark matter
detection experiments. A unique probe of mCP can be developed using underground
electrostatic accelerators that can directly accelerate mCPs above the
experimental thresholds of direct dark matter detection experiments.
