Signals of a Light Dark Force in the Galactic Center
  Recent evidence for an excess of gamma rays in the GeV energy range about the
Galactic Center have refocused attention on models of dark matter in the low
mass regime ($m_\chi \lesssim m_Z/2$). Because this is an experimentally
well-trod energy range, it can be a challenge to develop simple models that
explain this excess, consistent with other experimental constraints. We
reconsider models where the dark matter couples to dark photon, which has a
weak kinetic mixing to the Standard Model photon, or scalars with a weak mixing
with the Higgs boson. We focus on the light ($\lesssim 1.5 GeV$) dark mediator
mass regime. Annihilations into the dark mediators can produce observable gamma
rays through decays to $\pi^0$, through radiative processes when decaying to
charged particles ($e^+e^-, \mu^+\mu^-,...$), and subsequent interactions of
high energy $e^+e^-$ with gas and light. However, these models have no signals
of $\bar p$ production, which is kinematically forbidden. We find that in these
models, the shape of resulting gamma-ray spectrum can provide a good fit to the
excess at Galactic Center. We discuss further constraints from AMS-02, and find
regions of compatibility.
