Formação de estrutura em um universo viscoso

Abstract

The cosmological standard model considers dark matter and dark energy, important components to explain observed phenomena in the Universe, contribute for about 95% of the total cosmic energy budget, while baryons and radiation with a small fraction of less than 5% of the total cosmic energy. Cold Dark Matter is considered to have equation of state of zero pressure, however its nature is one of the greatest mysteries of cosmology, and assume a dust-like equation of state can be a mistake. Viscosities are constantly present in nature, and is natural to think that dark matter must also have viscous properties. In this work we consider the study of a dark matter with viscous properties, which have a nonzero equation of state with negative pressure (since viscosities are dissipative mechanisms). Two viscosities are considered here: bulk and shear. The main goal of this work is study how the inclusion of shear viscosity impacts on the structure formation. A secondary goal is to investigate the relation of shear viscosity with models of modi ed gravity, using a phenomenological parametrization.