Testing General Relativity using the Environmental Dependence of Dark
  Matter Halos
  In this Letter, we investigate the environmental dependence of dark matter
halos in theories that attempt to explain the accelerated expansion of the
Universe by modifying general relativity (GR). Using high-resolution N-body
simulations in f(R) gravity models which recover GR in dense environments by
virtue of the chameleon mechanism, we find a strong environmentally-dependent
difference between the lensing mass and dynamical mass estimates of dark matter
halos. This environmental dependence of the halo properties can be used as a
smoking gun to test GR observationally.
