Impact on the power spectrum of screening in modified gravity scenarios

We study the effects of screened modified gravity of the $f(R)$, dilaton and symmetron types on structure formation, from the quasilinear to the nonlinear regime, using semianalytical methods. For such models, where the range of the new scalar field is typically within the Mpc range and below in the cosmological context, nonlinear techniques are required to understand the deviations of the power spectrum of the matter density contrast compared to the ΛCDM template. This is nowadays commonly tackled using extensive N-body simulations. Here we present new results combining exact perturbation theory at the one-loop level (and a partial resummation of the perturbative series) with a halo model. The former allows one to extend the linear perturbative analysis up to k0.15h Mpc^-1 at the perturbative level while the latter leads to a reasonable, up to a few percent, agreement with numerical simulations for k3h Mpc^-1 for large-curvature $f(R)$ models, and k1h Mpc^-1 for dilatons and symmetrons, at $z=0$. We also discuss how the behaviors of the perturbative expansions and of the spherical collapse differ for $f(R)$, dilaton, and symmetron models.