The Dark Side of the Universe – Some Suggestions

Abstract

Only about 4% of the Universe’s composition is known and understood, while the remaining 96% is the unknown and mysterious. Ever since the concrete discovery of the dark matter (≈ 26% of the total Universe) by Vera Rubin (mainly)1 in 1970s (otherwise knownas the constantrotational velocitycurves profiles) and ofdark energy (≈ 70% of the total Universe’s energy density) by Adam Riess, Brian Schmidt, Saul Perlmutter and others in 1997, there have been many proposals for the both. The dark matter models contain quantum fields (mainly); scalar, vector and tensor; while other proposals rely on the modified gravity. The dark energy models could be categorized into two groups as: (1) the vacuum energy (non-dynamical); (2) the dynamical models. In the work presented in this thesis we do two things: (I) We explain the constant rotational velocity curves of the spiral galaxy in f(R) gravity. We showed that we can get the rotational velocity curves in f(R) gravity, in vacuum and in different 1Others include W. Kent Ford, Jr. and N. Thonnard. matterdistributionscenariosofthegalacticenvironment. WealsousedtheBrans-Dicke theory to get information about the dark matter (particle nature) and its behavior in the galactic environment. (II) We describe the dark energy to be a combination of both non-dynamical vacuum energy and dynamical energy. The non-dynamical vacuum energy comes from the minimum energy of the scalar Higgs potential while the dynamical part comes from the evolving Higgs fields. We argue that all the dark energy models must have some prior connection with Particle Physics no matter which category they fall in. For this reason, we take the extension of the standard model of the Particle Physics by including two Higgs doublets in two different scenarios and the extension of the two Higgs doublet model with different vacuua to show that we can get the accelerated expansion of the Universe from scalar fields already present in Particle Physics in the quintessential regime while satisfying all Particle Physics constrains.