Figure 28: Left panel: Linear matter power spectra for CDM (solid line; , )
and scalaron (dashed line; , ) cosmologies. The modification
to gravity causes a sizeable scale dependent effect in the growth of perturbations. The redshift
dependence of the scalaron can be seen by comparing the top and bottom pairs of power
spectra evaluated at redshifts and , respectively. Right panel: The environmental
dependent chameleon mechanism can be seen in the mildly nonlinear regime. We exhibit the fractional
difference between the and GR power spectra for the model
(1.8.37) with parameters and . The dashed lines represent
linear power spectra ( and calculated with no higher order effects) and the solid
lines are the power spectra calculated to second order. We see that the nonlinearities decrease the
modified gravity signal. This is a result of the chameleon mechanism. The top set of lines correspond
to and the bottom to ; demonstrating that the modified gravity signal dramatically
decreases for larger . This is due to the scalaron mass being much larger at higher redshifts.
Furthermore, nonlinear effects are less significant for increasing .
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