Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Hubble Tension in the Context of Cosmological Scalar Field Models(01. Izmir Institute of Technology, 2024) Alfar, Rand Abdel Latıf Suleıman; Erdem, RecaiThis thesis delves into the issue of Hubble tension that is the discrepancy between different types of measurements of the expansion rate of the universe at present (i.e. Hub- ble constant H0). Various techniques can be employed to measure H0. There are two types of measurements, namely, direct and indirect measurements for measurement of H0. Direct measurements involve determining the recession velocities of galaxies or supernovae at relatively small cosmological distances, so this type of measurements are direct local measurements. On the other hand, indirect measurements encompass both local methods, such as utilizing the Tully-Fisher relation, and non-local approaches, including cosmic microwave background (CMB) measurements and baryon acoustic oscillation (BAO) measurements of large-scale structures(LSS). The most precise local measurements are achieved through supernovae calibrated by Cepheid variable star measurements, while CMB measurements provide the most precise non-local measurements. However, even when considering measurement errors, there is a significant discrepancy between supernovae and CMB measurements. This is known as the Hubble tension. A milder discrepancy is also observed between local direct measurements and BAO measurements. Many different potential sources of this tension and many different models are proposed to resolve this tension. This thesis focuses on the subset of the proposed models that employ scalar fields in the context of general relativity. The primary objective is to provide a comprehensive understanding of the fundamental ideas underlying these models and emphasize their theoretical aspects.Master Thesis Extra time-like dimensions(Izmir Institute of Technology, 2006) Ün, Cem Salih; Erdem, RecaiThe current status of extra dimensions in high energy physics with particular emphasis on extra time-like dimensions is briefly reviewed. Some of the phenomenological problems related to the use of extra time-like dimensions that mentioned in the literature are reconsidered. It is found that the use of extra time-like dimensions is less problematic than it was previously thought.Master Thesis Dark Energy Mechanisms in the Context of Extra Dimensional Models(Izmir Institute of Technology, 2011) Yağmurcukardeş, Mehmet; Erdem, RecaiDark energy is the simplest and the most standart explanation to account for the observed accelerated expansion of the universe. In this thesis we use the term 'dark energy' in its standart meaning i.e. a field or fluid that is responsible for the cosmic acceleration in the frame work of general relativity. Meanwhile extra dimensions is an attractive framework to understand many otherwise unexplained physical phenomena in a clear, simple formulation. Therefore the study of extra dimensional cosmological models is an attractive area of study. In this thesis we have considered viability of extra dimensional cosmological models in the light of the accelerated expansion of the universe. We have confirmed the results of studies that have shown the incompatibility of a broad class of extra dimensional cosmological models with a dark energy of an equation of state close to that of cosmological constant. We have discussed also possible theoritical and vational ways to avoid the no-go theorems for extra dimensional cosmological models as well.Master Thesis Solitonic Solutions and Particle Localization in Higher Dimensional Spaces(Izmir Institute of Technology, 2003) Erman, Fatih; Erdem, RecaiFirst the basic extra dimensional theory (i.e. Kaluza-Klein theory) and the main aspects of solitons are reviewed. Then the current status of extra dimen-sional models and the application of solitons (especially kinks) in this context are studied. The extra dimensional models for fermion localization are considered with a particular emphasis. Finally a variation of these models which tries to in-corporate the best aspects of various models for fermion localization is presented.