Clipping the Cosmos II: Cosmological information from non-linear scales

Abstract

We present a method for suppressing contributions from higher-order terms in perturbation theory, greatly increasing the amount of information which may be extracted from the matter power spectrum. In an evolved cosmological density field the highest density regions are responsible for the bulk of the nonlinear power. By suitably down-weighting these problematic regions we find that the one- and two-loop terms are typically reduced in amplitude by ~70 per cent and ~95 per cent respectively, relative to the linear power spectrum. This greatly facilitates modelling the shape of the galaxy power spectrum, potentially increasing the number of useful Fourier modes by more than two orders of magnitude. We provide a demonstration of how this technique allows the galaxy bias and the amplitude of linear matter perturbations sigma_8 to be determined from the power spectrum on conventionally nonlinear scales, 0.1<k<0.7 h/Mpc.