Modelos cosmológicos com gás relativístico reduzido e com constantes gravitacional e cosmológica variáveis

Abstract

In this thesis we present a detailed review of some cosmological models, including the theory of linear cosmological perturbations for two distinct models which represent certain interest from the point of view of possible applications. All presented material comes from the recent literature and does not include original elements. However, the knowledge of these models opens a possibility of extensions which are now under discussion and development. At first it is presented a brief review of the Standard Cosmological Model, which can be associated with FLRW model (Friedmann-Lemaître-Robertson-Walker). The latter describes an expanding Universe marked by homogeneity and isotropy on a large scale. After that we discuss the model composite by a cosmic fluid described by reduced relativisticgas,betterknownbytheacronymRRG(reducedrelativisticgas). Theequation of state of the RRG model has a very close match to the model of gas of massive particles with relativistic kinetic energies. We consider the cosmological perturbations around the background of flat, homogeneous and isotropic RRG-based model. After that follows the discussion of the possibility of including perturbations of the gravitational constant G and the cosmological constant Λ within the model motivated by semiclassical corrections.