Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Investigating the parameter space of viable models for f(R) gravity
The accelerated expansion of spacetime intuitively points to the existence of new, unknown energy fields pervading the universe, but it is has also spurred the growth of the research field of modified gravity theories. Of these, f(R) theories of gravity is the first and simplest modification to Gene...
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Maths and Applied Maths
2020
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613170964627456 |
|---|---|
| access_status_str | Open Access |
| author | Kandhai, Sulona |
| author2 | Dunsby, Peter |
| author_browse | Dunsby, Peter Kandhai, Sulona |
| author_facet | Dunsby, Peter Kandhai, Sulona |
| author_sort | Kandhai, Sulona |
| collection | Thesis |
| description | The accelerated expansion of spacetime intuitively points to the existence of new, unknown energy fields pervading the universe, but it is has also spurred the growth of the research field of modified gravity theories. Of these, f(R) theories of gravity is the first and simplest modification to General Relativity, and have been studied extensively for their astrophysical and cosmological predictions. Power law f(R) modifications have been shown to exhibit desirable characteristics, producing the late time accelerated expansion as well as satisfying local tests of gravity. However, there is wide degeneracy among models in this class, and they are known to suffer from cosmological instabilities, which could lead to curvature singularities at finite times. This thesis addresses questions directly relating to model degeneracy and sudden singularities. Cosmologies and cosmological perturbations, resulting from a general broken power law modification to GR are generated, studied and evolved. Simulations are performed using 1+3 space time decomposition of the field equations and a dynamical systems approach to f(R) cosmology. The parameter space of this model, which includes the HuSawicki [6], Starobinsky [96] and Miranda [7] f(R) forms as subclasses, is investigated. It is found that there are regions in the parameter space which are completely singular and bound by continuous curves. We also investigate regions of the parameter space in which the attractive nature of gravity is preserved, and find that these regions intersect. The results of a Markov Chain Monte Carlo analysis significantly narrowed the viable region of the exponent parameter space of the general power law f(R) model. Current cosmological distance data; SNIa (Union 2), BAO (6dFGS, BOSS, SDSS, WiggleZ) as well as the LRG power spectrum (SDSS DR9), were used to obtain these constraints. The best fits are compared with the ΛCDM model, and leads to the conclusion that this class is still a candidate for the gravitational interaction. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/31181 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:31:53.390Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Department of Maths and Applied Maths |
| publisherStr | Department of Maths and Applied Maths |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/31181 Investigating the parameter space of viable models for f(R) gravity Kandhai, Sulona Dunsby, Peter de la Cruz, Alvaro Weltman, Amanda Applied Maths The accelerated expansion of spacetime intuitively points to the existence of new, unknown energy fields pervading the universe, but it is has also spurred the growth of the research field of modified gravity theories. Of these, f(R) theories of gravity is the first and simplest modification to General Relativity, and have been studied extensively for their astrophysical and cosmological predictions. Power law f(R) modifications have been shown to exhibit desirable characteristics, producing the late time accelerated expansion as well as satisfying local tests of gravity. However, there is wide degeneracy among models in this class, and they are known to suffer from cosmological instabilities, which could lead to curvature singularities at finite times. This thesis addresses questions directly relating to model degeneracy and sudden singularities. Cosmologies and cosmological perturbations, resulting from a general broken power law modification to GR are generated, studied and evolved. Simulations are performed using 1+3 space time decomposition of the field equations and a dynamical systems approach to f(R) cosmology. The parameter space of this model, which includes the HuSawicki [6], Starobinsky [96] and Miranda [7] f(R) forms as subclasses, is investigated. It is found that there are regions in the parameter space which are completely singular and bound by continuous curves. We also investigate regions of the parameter space in which the attractive nature of gravity is preserved, and find that these regions intersect. The results of a Markov Chain Monte Carlo analysis significantly narrowed the viable region of the exponent parameter space of the general power law f(R) model. Current cosmological distance data; SNIa (Union 2), BAO (6dFGS, BOSS, SDSS, WiggleZ) as well as the LRG power spectrum (SDSS DR9), were used to obtain these constraints. The best fits are compared with the ΛCDM model, and leads to the conclusion that this class is still a candidate for the gravitational interaction. 2020-02-20T09:15:06Z 2020-02-20T09:15:06Z 2019 2020-02-20T09:14:48Z Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/31181 eng application/pdf Department of Maths and Applied Maths Faculty of Science |
| spellingShingle | Applied Maths Kandhai, Sulona Investigating the parameter space of viable models for f(R) gravity |
| thesis_degree_str | Doctoral |
| title | Investigating the parameter space of viable models for f(R) gravity |
| title_full | Investigating the parameter space of viable models for f(R) gravity |
| title_fullStr | Investigating the parameter space of viable models for f(R) gravity |
| title_full_unstemmed | Investigating the parameter space of viable models for f(R) gravity |
| title_short | Investigating the parameter space of viable models for f(R) gravity |
| title_sort | investigating the parameter space of viable models for f r gravity |
| topic | Applied Maths |
| url | http://hdl.handle.net/11427/31181 |
| work_keys_str_mv | AT kandhaisulona investigatingtheparameterspaceofviablemodelsforfrgravity |