Chasing the nonlinear evolution of matter power spectrum with a numerical resummation method: Solution of closure equations

We present a new numerical scheme to treat the nonlinear evolution of cosmological power spectra. Governing equations for matter power spectra have been previously derived by a nonperturbative technique with closure approximation. Solutions of the resultant closure equations just correspond to the resummation of an infinite class of perturbation corrections, and they consistently reproduce the one-loop results of standard perturbation theory. We develop a numerical algorithm to solve closure evolutions in both perturbative and nonperturbative regimes. The present numerical scheme is particularly suited for examining nonlinear matter power spectrum in general cosmological models, including modified theory of gravity. As a demonstration, we study weakly nonlinear evolution of power spectrum in a class of modified gravity models, as well as various dark energy models.