The windows for kinetically mixed Z'-mediated dark matter and the
  galactic center gamma ray excess
  One of the simplest hidden sectors with signatures in the visible sector is
fermionic dark matter $\chi$ coupled to a $Z'$ gauge boson that has purely
kinetic mixing with the standard model hypercharge. We consider the combined
constraints from relic density, direct detection and collider experiments on
such models in which the dark matter is either a Dirac or a Majorana fermion.
We point out sensitivity to details of the UV completion for the Majorana
model. For kinetic mixing parameter $\epsilon \le 0.01$, only relic density and
direct detection are relevant, while for larger $\epsilon$, electroweak
precision, LHC dilepton, and missing energy constraints become important. We
identify regions of the parameter space of $m_\chi$, $m_{Z'}$, dark gauge
coupling and $\epsilon$ that are most promising for discovery through these
experimental probes. We study the compatibility of the models with the galactic
center gamma ray excess, finding agreement at the 2-3$\sigma$ level for the
Dirac model.
