Revising the Halofit Model for the Nonlinear Matter Power Spectrum

Based on a suite of state-of-the-art high-resolution N -body simulations, we revisit the so-called halofit model as an accurate fitting formula for the nonlinear matter power spectrum. While the halofit model has frequently been used as a standard cosmological tool to predict the nonlinear matter power spectrum in a universe dominated by cold dark matter, its precision has been limited by the low resolution of N -body simulations used to determine the fitting parameters, suggesting the necessity of an improved fitting formula at small scales for future cosmological studies. We run high-resolution N -body simulations for 16 cosmological models around the Wilkinson Microwave Anisotropy Probe best-fit cosmological parameters (one-, three-, five-, and seven-year results), including dark energy models with a constant equation of state. The simulation results are used to re-calibrate the fitting parameters of the halofit model so as to reproduce small-scale power spectra of the N -body simulations, while keeping the precision at large scales. The revised fitting formula provides an accurate prediction of the nonlinear matter power spectrum in a wide range of wavenumbers ( k ⩽ 30 h Mpc −1 ) at redshifts 0 ⩽ z ⩽ 10, with 5% precision for k ⩽ 1 h Mpc −1 at 0 ⩽ z ⩽ 10 and 10% for 1 ⩽ k ⩽ 10 h Mpc −1 at 0 ⩽ z ⩽ 3. We discuss the impact of the improved halofit model on weak-lensing power spectra and correlation functions, and show that the improved model better reproduces ray-tracing simulation results.