Chameleon dark energy models with characteristic signatures
  In chameleon dark energy models, local gravity constraints tend to rule out
parameters in which observable cosmological signatures can be found. We study
viable chameleon potentials consistent with a number of recent observational
and experimental bounds. A novel chameleon field potential, motivated by f(R)
gravity, is constructed where observable cosmological signatures are present
both at the background evolution and in the growth-rate of the perturbations.
We study the evolution of matter density perturbations on low redshifts for
this potential and show that the growth index today gamma_0 can have
significant dispersion on scales relevant for large scale structures. The
values of gamma_0 can be even smaller than 0.2 with large variations of gamma
on very low redshifts for the model parameters constrained by local gravity
tests. This gives a possibility to clearly distinguish these chameleon models
from the Lambda-Cold-Dark-Matter model in future high-precision observations.
