Environmental screening of dark matter haloes in $f(R)$ gravity
  In certain theories of modified gravity, solar system constraints on
deviations from general relativity (GR) are satisfied by virtue of a so-called
screening mechanism, which enables the theory to revert to GR in regions where
the matter density is high or the gravitational potential is deep. In the case
of chameleon theories, the screening has two contributions -- self-screening,
which is due to the mass of an object itself, and environmental screening,
which is caused by the surrounding matter -- which are often entangled, with
the second contribution being more crucial for less massive objects. A
quantitative understanding of the effect of the environment on the screening
can prove critical in observational tests of such theories using systems such
as the Local Group and dwarf galaxies, for which the environment may be
inferred in various ways. We use the high-resolution {\sc liminality}
simulation of Shi et al. (2015) to test the fidelity of different definitions
of environment. We find that, although the different ways to define environment
in practice do not agree with one another perfectly, they can provide useful
guidance, and cross checks about how well a dark matter halo is screened. In
addition, the screening of subhaloes in dark matter haloes is primarily
determined by the environment, with the subhalo mass playing a minor role,
which means that lower-resolution simulations where subhaloes are not well
resolved can still be useful for understanding the modification of gravity
inside subhaloes.
