Figure 28

Figure 28: Left panel: Linear matter power spectra for ΛCDM (solid line; M −1 = 0 0, ν = 1.5) and scalaron (dashed line; −1 28 −1 − 1 M 0 = 375[10 h eV ], ν = 1.5) 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 z = 0.0 and z = 1.5, respectively. Right panel: The environmental dependent chameleon mechanism can be seen in the mildly nonlinear regime. We exhibit the fractional difference (P (k) − PGR (k))∕PGR (k) between the f(R) and GR power spectra for the model (1.8.37View Equation) with parameters − 1 28 −1 −1 M 0 = 375[10 h eV ] and ν = 1.5. The dashed lines represent linear power spectra (P (k) and PGR (k ) 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 z = 0 and the bottom to z = 0.9; demonstrating that the modified gravity signal dramatically decreases for larger z. This is due to the scalaron mass being much larger at higher redshifts. Furthermore, nonlinear effects are less significant for increasing z.