SOME COSMOLOGICAL CONSEQUENCES OF HIGHER DIMENSIONAL KLEIN-GORDON-RASTALL THEORY

• Main Author: Ari Widianto, Tegar
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/75305
• Institution: Institut Teknologi Bandung

The Rastall theory is proposed to modify the theory of general relativity (GR) by assuming that the conservation of the energy-momentum tensor (EMT) no longer holds in curved spacetime. The scalar field model was initially proposed as an alternative to the cosmological constant problem and later became an alternative model for dark energy (quintessence). One form of scalar field that has been proposed and naturally emerges in various physical theories is a field with an exponential potential. This study aims to investigate the cosmological consequences of the combination of these two models, the Rastall theory and the scalar field, referred to as the Klein-Gordon-Rastall (KGR) model, in higher-dimensional spacetime using the method of dynamical system analysis. From there, we attempt to explain the phenomena of inflation in the early universe and dark energy, which is the component causing the current accelerated expansion of the universe. Based on our interpretation, the inflationary model is characterized by an unstable solution, while the dark energy model is represented by a stable solution. We demonstrate that the exact solution of power-law inflation (PLI) can still be obtained in the KGR cosmological model, where the perfect fluid does not completely vanish, although its contribution is very small during inflation. The presence of a non-conservative EMT’s perfect fluid during the inflationary epoch in the KGR model is introduced to mimic the presence of other scalar fields (fluid representation) that coexist with the inflaton during the inflationary era. In addition, the perfect fluid in the inflation era can also be regarded as a fluid that represents radiation or vacuum. By incorporating a fluid with non-conservative EMT following the Rastall equation, the parameters of PLI can be enhanced even with a steep potential of the scalar field. This phenomenon can be seen as an alternative way for increasing PLI parameter instead of adding an interaction term between the inflaton and radiation matter as it yields similar consequences. On the other hand, this model can also provide an alternative explanation for the cosmic coincidence problem, where our current universe represents the latetime attractors of KGR cosmology, thus the KGR model can mimic the behavior of the ?CDM model in the late-time era. Therefore, the combination of scalar fields and non-conservative EMT of baryonic matter and dark matter plays a role as dark energy responsible for the current accelerated expansion of the universe.