Dark Forces and Light Dark Matter
  We consider a simple class of models in which the dark matter, X, is coupled
to a new gauge boson, phi, with a relatively low mass (m_phi \sim 100 MeV-3
GeV). Neither the dark matter nor the new gauge boson have tree-level couplings
to the Standard Model. The dark matter in this model annihilates to phi pairs,
and for a coupling of g_X \sim 0.06 (m_X/10 GeV)^1/2 yields a thermal relic
abundance consistent with the cosmological density of dark matter. The phi's
produced in such annihilations decay through a small degree of kinetic mixing
with the photon to combinations of Standard Model leptons and mesons. For dark
matter with a mass of \sim10 GeV, the shape of the resulting gamma-ray spectrum
provides a good fit to that observed from the Galactic Center, and can also
provide the very hard electron spectrum required to account for the observed
synchrotron emission from the Milky Way's radio filaments. For kinetic mixing
near the level naively expected from loop-suppressed operators (epsilon \sim
10^{-4}), the dark matter is predicted to scatter elastically with protons with
a cross section consistent with that required to accommodate the signals
reported by DAMA/LIBRA, CoGeNT and CRESST-II.
