Resumo: We consider the late Universe deep inside the cell of uniformity. At these scales, the Universe is highly inhomogeneous and is filled with discrete distributed structures (galaxies, groups and clusters of galaxies), which perturb the background Friedmann model. We investigate such Universe in the mechanical approach. This means that the peculiar velocities of the inhomogeneities in the form of galaxies as well as fluctuations of other perfect fluids are nonrealistic. Under such condition, we investigate the theory of scalar perturbations. We derive the main equations and apply them to a number of models, starting with the LambdaCDM model. We demonstrate that within our approach, the theory of scalar perturbations is a good tool to select viable dark energy models.

Funded by the Portuguese Government through the FCT – Fundação para a Ciência e a Tecnologia under the project UID/MAT/00212/2013

Resumo: We consider Kaluza-Klein (KK) models where internal spaces are compact Einstein spaces. These spaces are stabilized by background matter (e.g., monopole form-fields). We perturb this background by a compact matter source (e.g., the system of gravitating masses) with the zero pressure in the external/our space and an arbitrary pressure in the internal space. We show that the Einstein equations are compatible only if the matter source is smeared over the internal space and perturbed metric components do not depend on coordinates of extra dimensions. The latter means the absence of KK modes corresponding to the metric fluctuations. Maybe, the absence of KK particles in LHC experiments is explained by such mechanism.

Seminário realizado com o apoio do Centro de Matemática – 212 (Pest-OE/MAT/UI0212/2014).

Resumo: We consider the Universe deep inside the cell of uniformity which is of the order of 190 Mpc. At these scales, the Universe is filled with inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies), which perturb the background Friedmann model. Here, the mechanical approach is the most appropriate to describe the dynamics of the inhomogeneities which is defined, on the one hand, by gravitational potentials of inhomogeneities and, on the other hand, by the cosmological expansion of the Universe. As an example, we consider a possible collision between the Milky Way and Andromeda in future.

Seminário realizado com o apoio do Centro de Matemática – 212 (Pest-OE/MAT/UI0212/2014).