Extended Chameleons
  We extend the chameleon models by considering Scalar-Fluid theories where the
coupling between matter and the scalar field can be represented by a quadratic
effective potential with density-dependent minimum and mass. In this context,
we study the effects of the scalar field on Solar System tests of gravity and
show that models passing these stringent constraints can still induce large
modifications of Newton's law on galactic scales. On these scales we analyse
models which could lead to a percent deviation of Newton's law outside the
virial radius. We then model the dark matter halo as a Navarro-Frenk-White
profile and explicitly find that the fifth force can give large contributions
around the galactic core in a particular model where the scalar field mass is
constant and the minimum of its potential varies linearly with the matter
density. At cosmological distances, we find that this model does not alter the
growth of large scale structures and therefore would be best tested on galactic
scales, where interesting signatures might arise in the galaxy rotation curves.
