Cosmological nonlinear structure formation in full general relativity
  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.
