Systematic simulations of modified gravity: chameleon models
  In this work we systematically study the linear and nonlinear structure
formation in chameleon theories of modified gravity, using a generic
parameterisation which describes a large class of models using only 4
parameters. For this we have modified the N-body simulation code ECOSMOG to
perform a total of 65 simulations for different models and parameter values,
including the default LCDM. These simulations enable us to explore a
significant portion of the parameter space. We have studied the effects of
modified gravity on the matter power spectrum and mass function, and found a
rich and interesting phenomenology where the difference with the LCDM paradigm
cannot be reproduced by a linear analysis even on scales as large as
k~0.05h/Mpc, since the latter incorrectly assumes that the modification of
gravity depends only on the background matter density. Our results show that
the chameleon screening mechanism is significantly more efficient than other
mechanisms such as the dilaton and symmetron, especially in high-density
regions and at early times, and can serve as a guidance to determine the parts
of the chameleon parameter space which are cosmologically interesting and thus
merit further studies in the future.
