Structure formation with scalar field dark matter: the field approach

TL;DR

This paper explores how scalar field dark matter influences cosmic structure formation, showing it can lead to earlier galaxy formation and virialized structures compared to traditional cold dark matter models.

Contribution

It introduces a detailed field approach to scalar dark matter, deriving evolution equations and analyzing structure formation in both linear and nonlinear regimes.

Findings

Scalar field dark matter can form virialized structures.

Structure formation can occur earlier than in cold dark matter models.

Scalar perturbations exhibit oscillating growth modes.

Abstract

We study the formation of structure in the Universe assuming that dark matter can be described by a scalar field $\tilde{\Phi}$ with a potential $V(\Phi)=-\mathfrak{m}^{2}\tilde{\Phi}^{2}/2+\lambda\tilde{\Phi}^4/4$. We derive the evolution equations of the scalar field in the linear regime of perturbations. We investigate the symmetry breaking and possibly a phase transition of this scalar field in the early Universe. At low temperatures, the scalar perturbations have an oscillating growing mode and therefore, this kind of dark matter could lead to the formation of gravitational structures. In order to study the nonlinear regime, we use the spherical collapse model and show that, in the quadratic potential limit, this kind of dark matter can form virialized structures. The main difference with the traditional Cold Dark Matter paradigm is that the formation of structure in the scalar field model can occur at earlier times. Thus, if the dark matter is of scalar field nature we expect to have large galaxies at high redshifts.