A Unified Description of Screened Modified Gravity
  We consider modified gravity models driven by a scalar field whose effects
are screened in high density regions due to the presence of non-linearities in
its interaction potential and/or its coupling to matter. Our approach covers
chameleon, f(R) gravity, dilaton and symmetron models and allows a unified
description of all these theories. We find that the dynamics of modified
gravity are entirely captured by the time variation of the scalar field mass
and its coupling to matter evaluated at the cosmological minimum of its
effective potential, where the scalar field sits since an epoch prior to Big
Bang Nucleosynthesis. This new parameterisation of modified gravity allows one
to reconstruct the potential and coupling to matter and therefore to analyse
the full dynamics of the models, from the scale dependent growth of structures
at the linear level to non-linear effects requiring N-body simulations. This
procedure is illustrated with explicit examples of reconstruction for
chameleon, dilaton, f(R) and symmetron models.
