An exotic Universe : from dark energy to wormholes
May, 2021174 pages
Supervisors:
Thesis: PhD - ,
- Lisbon U.
- Published: May, 2021
URN/HDL:
Citations per year
0 Citations
Abstract: (U. Lisbon (main))
This thesis deals with extensions of General Relativity and their application to Cosmology and Gravitation. The introduction and main motivations of this essay can be found on Chapter 1.
The second chapter proposes a dark energy model driven by a scalar field kinetically coupled
to matter. The dynamics of the system are analysed through dynamical systems techniques. The background is evolved and the solutions are meticulously studied, focusing on the influence of the coupling on the cosmological parameters. Through the Planck constraints, it is derived anupper bound on the coupling parameter.
Chapter three is devoted to the analysis of a conformally coupled quintessence model in which the background expansion is set to mimic a CDM evolution. Both the background and linear perturbations are analysed. The growth of structures is tested against redshift space distortions data. The spherical collapse and cluster number counts are explored, and we shed some light on the possibility to distinguish between theoretical models with regard to two surveys.
An alternative formulation of General Relativity, where gravity is mediated by nonmetricity, on a flat and torsion free spacetime is exposed on the fourth Chapter. The background dynamics are set to follow the same evolution as in the standard model of Cosmology. The linear matter perturbations are evolved and the f 8 parameter is tested against large scale observations in the late Universe.
Chapter five introduces a 3-form field to the Einstein-Hilbert action in the context of gravitation.
Specifically, it is found wormhole solutions where the ordinary matter fields are able to coexist throughout spacetime without violating the classical energy conditions. On such scenario, the 3-form field is responsible for holding the throat of the wormhole open.
On Chapter six the gravitational Lagrangian for modified Gauss-Bonnet gravity is reconstructed, such that the Friedmann equation of a bouncing Universe is recovered.- Energia escura acoplada
- Colapso esférico
- Buracos de verme
- Não-metricidade
- Cosmologias ressalto
- mediation: gravitation
- quintessence: coupling
- action: Einstein-Hilbert
- expansion: background
- perturbation: linear
References(345)
Figures(0)
- [1]
- [2]
- [3]
- [4]
- [5]
- [6]
- [7]
- [8]
- [9]
- [10]
- [11]
- [12]
- [13]
- [14]
- [15]
- [16]
- [17]
- [18]
- [19]
- [20]
- [21]
- [22]
- [23]
- [24]
- [25]