Quando Gravitação e Cosmologia Destoam do Padrão : Testando MOND e modelos de unificação do setor escuro

Abstract

The aim of this thesis is to investigate alternative ideas for the standard cosmology (here,denoted by the?CDM model). The two main ingredients of such standard description ofthe cosmic medium are cold dark matter (CDM) and dark energy (DE), which together formthe dark sector. We start our discussion with an alternative description of the dark matterphenomena. We aply the Modified Newtonian Dynamics (MOND) to the COMA galaxy clusterin order to explain the large mass to light ratio of such system. This corresponds to the“astrophysical part” of this work. At the end of chapter 3 we state that dark matter is afundamental component of the cosmic energy budget. Then, it occurs a transition into thethesis. Chapters 5, 6 and 7 (the “cosmological part”) are devoted to unified models for the darksector. In some sense, we are dealing now with alternatives to thedark energy phenomena. Inthis unification scenario, DM and DE are different manifestations of a single dark component.The Chaplygin gas and the bulk viscous fluid realize this idea. The homogeneous and isotropicbackground dynamics of these candidates is well compatible with the data (in particular, weuse Supernovae, Gamma Ray-Bursts, indirectH(z)measurements). However, we discuss indetail de differences between the perturbative dynamics of theChaplygin (adiabatic) modeland the bulk viscous (nonadiabatic) one. At the perturbative level our cosmological probesare the matter power spectrum and the integrated Sachs-Wolfe effect. There appears somepathologies with these alternative components what bring our attentions back to the standardcosmology. Within the?CDM conception for the Universe we relax the assuption that CDMis a ideal fluid make it “more real” by adding to its energy momentumtensor a dissipativecomponent (given by the bulk viscous pressure). This gives rise to the?vCDM model studiedin chapter 7. We find that the current cosmological data allows CDM to have a viscosity of=109Pa.seg. In some sense, we hope that this result could mean a new prediction to be testedin the future CDM laboratories.