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Structure formation with viscous dark matter
Thesis (MSc)--Stellenbosch University, 2025.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614007374905344 |
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| access_status_str | Open Access |
| author | Van der Merwe, Jaymie |
| author2 | John, A. J. |
| author_browse | John, A. J. Van der Merwe, Jaymie |
| author_facet | John, A. J. Van der Merwe, Jaymie |
| author_sort | Van der Merwe, Jaymie |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132371 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:45:11.659Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132371 Structure formation with viscous dark matter Van der Merwe, Jaymie John, A. J. Stellenbosch University. Faculty of Science. Dept. of Physics. Viscosity -- Mathematical models Dark matter (Astronomy) -- Mathematical models Cosmology -- Mathematical models UCTD Thesis (MSc)--Stellenbosch University, 2025. van der Merwe, J. 2025. Structure Formation with Viscous Dark Matter. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/ae2e804d-e433-4955-b353-6ecd72a8d4da ENGLISH ABSTRACT: Advancements in observational cosmology have resulted in discrepancy between theory and observation, challenging our understanding of the universe through the ΛCDM model. The most statistically significant of these discrepancies being the so-called Hubble tension. These tensions have sparked a wide array of extensions to the ΛCDM model. Many of these extensions propose new physics through new types of matter which often lack observational evidence themselves. Another, more phenomenological, approach can be taken through adding additional degrees of freedom to the ΛCDM model. An example of this is the introduction of bulk viscous pressure where one forgoes the perfect fluid model. Studies have shown that bulk viscosity can suppress the growth of the dark matter density perturbations possibly alleviating the problems faced on small scales. Most commonly, the work done in bulk viscous cosmology uses the Eckart theory due to its simplicity but the full Muller-Israel-Stewart (MIS) theory has not been investigated to the same extent. A major pathology of the Eckart theory is that it is non-causal. The full Muller-Israel-Stewart (MIS) theory for dissipative hydrodynamics rectifies this issue. We present an analysis of the impact of bulk viscosity on the evolution of Newtonian cold dark matter. We perform this analysis for the Eckart and MIS theories. We present the resulting fluid equations as well as the evolution equation for the bulk viscous dark matter density perturbations. We compare the evolution of the perturbations in the different theories to each other as well as to known results from literature. We also present a partial analysis of the relativistic regime where we study bulk viscous pressure and its impact on the evolution of the metric potential. In both cases we solve the evolution equations numerically and make qualitative statements regarding their impact on structure formation. AFRIKAANSE OPSOMMING: Onlangse ontwikkelinge in waarnemingskosmologie toon ’n teenstrydigheid tus- sen die teorie en die waarneembares, wat gevolglik ons begrip van die heelal volgens die ΛCDM model bevraagteken. Onder meer is die statisties beteke- nisvolste teenstrydigheid die sogenaamde Hubble-spanning. Hierdie spanninge het menigte toevoegings tot die ΛCDM-model geïnspireer. Baie van hierdie toevoegings stel voor nuwe fisika deur die insluiting van nuwe tipes materie of wat dikwels self gebrekkig aan waarneembare bewyse is. ’n Ander, meer fenomenologiese, benadering kan gevolg word deur addisionele vryheidsgrade tot die ΛCDM-model by te voeg. ’n Voorbeeld hiervan is om afskeid te neem van ’n perfekte vloeimodel, met die toevoeging van ’n viskose volumedruk. Viskose volume kosmologie word hoofsaaklik met Eckart-teorie hanteer vanweë sy eenvoud, maar dat Eckart-teorie ’n nie-oorsaaklike teorie is, is ’n groot tekortkoming. Die volledige Muller-Israel-Stewart (MIS)-teorie vir dissipatiewe hidrodinamika regstel hierdie probleem. Hierdie werk analiseer die impak van viskose volumedruk op die evolusie van Newtoniese koue don- ker materie. Ons voer hierdie analise uit vir die Eckart- en MIS-teorieë. Ons gee die resulterende vloeivergelykings sowel as die evolusie-vergelyking vir die viskose volume donker materie digtheidversteurings. Ons vergelyk die versteu- ringsevolusie van die verskillende teorieë met mekaar, sowel as met bekende resultate uit die literatuur. Ons gee ook ’n gedeeltelike analise van die relatiwistiese regime, waar die viskose volumedruk en die impak daarvan op die evolusie van die metrieke potensiaal bestudeer word. In beide gevalle word die evolusievergelykings nu- meries opgelos en kwalitatiewe stellings oor hul impak op struktuurvorming gemaak. Masters 2025-06-05T08:00:07Z 2025-06-05T08:00:07Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132371 en Stellenbosch University xi, 101 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Viscosity -- Mathematical models Dark matter (Astronomy) -- Mathematical models Cosmology -- Mathematical models UCTD Van der Merwe, Jaymie Structure formation with viscous dark matter |
| title | Structure formation with viscous dark matter |
| title_full | Structure formation with viscous dark matter |
| title_fullStr | Structure formation with viscous dark matter |
| title_full_unstemmed | Structure formation with viscous dark matter |
| title_short | Structure formation with viscous dark matter |
| title_sort | structure formation with viscous dark matter |
| topic | Viscosity -- Mathematical models Dark matter (Astronomy) -- Mathematical models Cosmology -- Mathematical models UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132371 |
| work_keys_str_mv | AT vandermerwejaymie structureformationwithviscousdarkmatter |