Nonlinear structure formation in the Cubic Galileon gravity model
  We model the linear and nonlinear growth of large scale structure in the
Cubic Galileon gravity model, by running a suite of N-body cosmological
simulations using the {\tt ECOSMOG} code. Our simulations include the
Vainshtein screening effect, which reconciles the Cubic Galileon model with
local tests of gravity. In the linear regime, the amplitude of the matter power
spectrum increases by $\sim 25%$ with respect to the standard $\Lambda$CDM
model today. The modified expansion rate accounts for $\sim 20%$ of this
enhancement, while the fifth force is responsible for only $\sim 5%$. This is
because the effective unscreened gravitational strength deviates from standard
gravity only at late times, even though it can be twice as large today. In the
nonlinear regime ($k \gtrsim 0.1 h\rm{Mpc}^{-1}$), the fifth force leads to
only a modest increase ($\lesssim 8%$) in the clustering power on all scales
due to the very efficient operation of the Vainshtein mechanism. Such a strong
effect is typically not seen in other models with the same screening mechanism.
The screening also results in the fifth force increasing the number density of
halos by less than 10%, on all mass scales. Our results show that the screening
does not ruin the validity of linear theory on large scales which anticipates
very strong constraints from galaxy clustering data. We also show that, whilst
the model gives an excellent match to CMB data on small angular scales ($l
\gtrsim 50$), the predicted integrated Sachs-Wolf effect is in tension with
Planck/WMAP results.
