  We investigate the environment dependence of dark matter halos in the
symmetron modified gravity scenario. The symmetron is one of three known
mechanisms for screening a fifth-force and thereby recovering General
Relativity in dense environments. The effectiveness of the screening depends on
both the mass of the object and the environment it lies in. Using
high-resolution N-body simulations we find a significant difference, which
depends on the halos mass and environment, between the lensing and dynamical
masses of dark matter halos similar to the f(R) modified gravity. The symmetron
can however yield stronger signatures due to a freedom in the strength of the
coupling to matter.
