New Constraints on Isospin-Violating Dark Matter
  We derive bounds on the dark matter annihilation cross-section for low-mass
(5-20 GeV) dark matter annihilating primarily to up or down quarks, using the
Fermi-LAT bound on gamma-rays from Milky Way satellites. For models in which
dark matter-Standard Model interactions are mediated by particular contact
operators, we show that these bounds can be directly translated into bounds on
the dark matter-proton scattering cross-section. For isospin-violating dark
matter, these constraints are tight enough to begin to constrain the
parameter-space consistent with experimental signals of low-mass dark matter.
We discuss possible models that can evade these bounds.
