Cosmological nonlinear structure formation in full general relativity

TL;DR

This paper uses numerical relativity to study nonlinear structure formation in cosmology, comparing dust and scalar field dark matter models, and finds differences in collapse times and power spectrum cut-offs.

Contribution

It provides the first full general relativistic numerical simulations of nonlinear cosmological structure formation with both dust and scalar field matter models.

Findings

Scalar field introduces a cutoff in the power spectrum at the Compton wavelength.

Perturbations grow similarly in linear regime for both models.

Collapse occurs faster in dust-dominated universes in the nonlinear regime.

Abstract

We perform numerical evolutions of cosmological scenarios using a standard general relativistic code in spherical symmetry. We concentrate on two different situations: initial matter distributions that are homogeneous and isotropic, and perturbations to those that respect the spherical symmetry. As matter models we consider the case of a pressureless perfect fluid, i.e. dust, and the case of a real massive scalar field oscillating around the minimum of the potential. Both types of matter have been considered as possible dark matter candidates in the cosmology literature, dust being closely related to the standard cold dark matter paradigm. We confirm that in the linear regime the perturbations associated with these types of matter grow in essentially the same way, the main difference being that in the case of a scalar field the dynamics introduce a cut-off in the power spectrum of the density perturbations at scales comparable with the Compton wavelength of the field. We also follow the evolutions well beyond the linear regime showing that both models are able to form structure. In particular we find that, once in the nonlinear regime, perturbations collapse faster in a universe dominated by dust. This is expected to delay the formation of the first structures in the scalar field dark matter scenario with respect to the standard cold dark matter one.