Dark Photons from the Center of the Earth: Smoking-Gun Signals of Dark
  Matter
  Dark matter may be charged under dark electromagnetism with a dark photon
that kinetically mixes with the Standard Model photon. In this framework, dark
matter will collect at the center of the Earth and annihilate into dark
photons, which may reach the surface of the Earth and decay into observable
particles. We determine the resulting signal rates, including Sommerfeld
enhancements, which play an important role in bringing the Earth's dark matter
population to their maximal, equilibrium value. For dark matter masses $m_X
\sim$ 100 GeV - 10 TeV, dark photon masses $m_{A'} \sim$ MeV - GeV, and kinetic
mixing parameters $\varepsilon \sim 10^{-10} - 10^{-8}$, the resulting
electrons, muons, photons, and hadrons that point back to the center of the
Earth are a smoking-gun signal of dark matter that may be detected by a variety
of experiments, including neutrino telescopes, such as IceCube, and space-based
cosmic ray detectors, such as Fermi-LAT and AMS. We determine the signal rates
and characteristics, and show that large and striking signals---such as
parallel muon tracks---are possible in regions of the $(m_{A'}, \varepsilon)$
plane that are not probed by direct detection, accelerator experiments, or
astrophysical observations.
