Chasing the non-linear evolution of matter power spectrum with numerical resummation method: solution of closure equations

We present a new numerical scheme to treat the non-linear evolution of cosmological power spectra. Governing equations for matter power spectra have been previously derived by a non-perturbative 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 non-perturbative regimes. The present numerical scheme is particularly suited for examining non-linear matter power spectrum in general cosmological models, including modified theory of gravity. As a demonstration, we study weakly non-linear evolution of power spectrum in a class of modified gravity models, as well as various dark energy models.Comment: 17 pages, 8 figures; Fig.3 updated and typos fixe

Reconstruction of primordial tensor power spectra from B-mode polarization of the cosmic microwave background

Given observations of B-mode polarization power spectrum of the cosmic microwave background (CMB), we can reconstruct power spectra of primordial tensor modes from the early Universe without assuming their functional form such as a power-law spectrum. Shape of the reconstructed spectra can then be used to probe the origin of tensor modes in a model-independent manner. We use the Fisher matrix to calculate the covariance matrix of tensor power spectra reconstructed in bins. We find that the power spectra are best reconstructed at wavenumbers in the vicinity of $k\approx 6\times 10^{-4}$ and $5\times 10^{-3}~{\rm Mpc}^{-1}$, which correspond to the "reionization bump" at $\ell\lesssim 6$ and "recombination bump" at $\ell\approx 80$ of the CMB B-mode power spectrum, respectively. The error bar between these two wavenumbers is larger because of lack of the signal between the reionization and recombination bumps. The error bars increase sharply towards smaller (larger) wavenumbers because of the cosmic variance (CMB lensing and instrumental noise). To demonstrate utility of the reconstructed power spectra we investigate whether we can distinguish between various sources of tensor modes including those from the vacuum metric fluctuation and SU(2) gauge fields during single-field slow-roll inflation, open inflation and massive gravity inflation. The results depend on the model parameters, but we find that future CMB experiments are sensitive to differences in these models. We make our calculation tool available on-line.Comment: 9 pages, 2 figures, 4 tables; accepted version in Phys. Rev.

Beyond consistency test of gravity with redshift-space distortions at quasi-linear scales

Redshift-space distortions (RSD) offer an attractive method to measure the growth of cosmic structure on large scales, and combining with the measurement of the cosmic expansion history, it can be used as cosmological tests of gravity. With the advent of future galaxy redshift surveys aiming at precisely measuring the RSD, an accurate modeling of RSD going beyond linear theory is a critical issue in order to detect or disprove small deviations from general relativity (GR). While several improved models of RSD have been recently proposed based on the perturbation theory (PT), the framework of these models heavily relies on GR. Here, we put forward a new PT prescription for RSD in general modified gravity models. As a specific application, we present theoretical predictions of the redshift-space power spectra in f(R) gravity model, and compare them with N-body simulations. Using the PT template that takes into account the effects of both modifications of gravity and RSD properly, we successfully recover the fiducial model parameter in N-body simulations in an unbiased way. On the other hand, we found it difficult to detect the scale dependence of the growth rate in a model-independent way based on GR templates.Comment: 17 pages, 9 figures, version accepted for publication in PR