Towards accurate cosmological predictions for rapidly oscillating scalar fields as dark matter

TL;DR

This paper introduces a new method for analyzing the cosmological evolution of scalar fields as dark matter, improving accuracy in predictions for linear perturbations and implications for cosmological observables.

Contribution

A novel approach to scalar field cosmology that simplifies analysis and enhances understanding of dark matter properties and perturbation suppression.

Findings

The Jeans wavenumber $k_J = a d7 \, \sqrt{mH}$ relates to perturbation suppression.

Semi-analytical results match full numerical solutions from an amended CMB code.

The new method offers better predictions for cosmological observables.

Abstract

As we are entering the era of precision cosmology, it is necessary to count on accurate cosmological predictions from any proposed model of dark matter. In this paper we present a novel approach to the cosmological evolution of scalar fields that eases their analytic and numerical analysis at the background and at the linear order of perturbations. We apply the method to a scalar field endowed with a quadratic potential and revisit its properties as dark matter. Some of the results known in the literature are recovered, and a better understanding of the physical properties of the model is provided. It is shown that the Jeans wavenumber defined as $k_J = a \sqrt{mH}$ is directly related to the suppression of linear perturbations at wavenumbers $k>k_J$. We also discuss some semi-analytical results that are well satisfied by the full numerical solutions obtained from an amended version of the CMB code CLASS. Finally we draw some of the implications that this new treatment of the equations of motion may have in the prediction for cosmological observables.