The matter power spectrum as a test of cosmological models

Abstract

Initial conditions for the evolution of energy density perturbations are generally specified at some initial time very early during the radiation dominated regime. If, instead, the amplitude of density perturbations is specified at horizon crossing like in the Harrison-Zeldovich prescription, the equations of evolution have to be solved during the subsequent subhorizon evolution. Using this ansatz we show how to construct observables such as the matter power spectrum of generic dark energy models from the power spectrum of a ΛCDM model without the need of solving in full the dynamical equations describing the evolution of all energy density perturbations. This saves a lot of effort. Our approach allows to make model predictions of observable quantities that can be expressed in terms of the matter power spectrum alone, such as the amplitude of matter fluctuations, peculiar velocities, cosmic microwave background temperature anisotropies on large angular scales, or the weak lensing convergence spectrum.