Leptophilic Dark Matter with $Z'$ interactions
  We consider a scenario where dark matter (DM) interacts exclusively with
Standard Model (SM) leptons at tree level. Due to the absence of tree-level
couplings to quarks, the constraints on leptophilic dark matter arising from
direct detection and hadron collider experiments are weaker than those for a
generic WIMP. We study a simple model in which interactions of DM with SM
leptons are mediated by a leptophilic $Z'$ boson, and determine constraints on
this scenario arising from relic density, direct detection, and other
experiments. We then determine current LHC limits and project the future
discovery reach. We show that, despite the absence of direct interactions with
quarks, this scenario can be strongly constrained.
