  We outline the science opportunities in the areas of searches for dark matter
and new physics offered by a proposed future MeV gamma-ray telescope, the
Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO). We
point out that such an instrument would play a critical role in opening up a
discovery window for particle dark matter with mass in the MeV or sub-MeV
range, in disentangling the origin of the mysterious 511 keV line emission in
the Galactic Center region, and in potentially discovering Hawking evaporation
from light primordial black holes.
