This thesis includes two independent works on dark energy and the cosmic dark ages.
(1) Weinberg {\it et al.} calculated the anthropic likelihood of the cosmological constant $\Lambda$ using a model assuming that the number of observers is proportional to the total mass of gravitationally collapsed objects, with mass greater than a certain threshold at $t \to \infty$. We modify Weinberg`s model in a way that the number of observers is proportional to the number of collapsed objects, with mass and time equal to certain preferred mass and time scales. Unlike Weinberg`s model, the anthropic likelihood of the primordial density perturbation amplitude $Q$ from our model explains $Q_0$ well without any additional constraint. Furthermore, observers will be affected by the history of the collapsed object, and we introduce a method to calculate the anthropic likelihoods of $\Lambda$ and $Q$ from the mass history using the extended Press-Schechter formalism. In contrast to models using only a single mass constraint, the results from the models using the mass history are robust even if we allow both $\Lambda$ and $Q$ to vary.
(2) We propose a topological analysis method of 21-cm signal using the 2D genus curve,
a function defined as the difference of the number of hot regions and the number of cold regions, compared to a given temperature. We show that the 2D genus curve of the differential brightness temperature, $g_\mathrm{2D} (\delta T_\mathrm{b})$, by comparing to $g_\mathrm{2D}$ of the density fluctuation, $g_\mathrm{2D} (\delta T_\mathrm{b,n})$, clearly shows the evolution of the reionization process. We also show that the 2D genus topology method can effectively distinguish different reionization scenarios, especially with different source photon efficiency for a low-mass source $10^8 \lesssim M / M_\odot \lesssim 10^9$ and with different greatest ionized bubble size. In terms of the design of future detection, we show that observational beams insensitive to la...

- Description
- 한국과학기술원 : 물리학과,

- Publisher
- 한국과학기술원

- Issue Date
- 2011

- Identifier
- 466329/325007 / 020047999

- Language
- eng

- Description
학위논문(박사) - 한국과학기술원 : 물리학과, 2011.2, [ viii, 48p. ]

- Keywords
Cosmic Reionization; Anthropic Principle; Cosmological Constant; Cosmology; 2D Genus Topology; 2차원 종수 함수 분석법; 우주 재이온화; 인간 중심적 원리; 우주 상수; 우주론

- Appears in Collection
- PH-Theses_Ph.D.(박사논문)

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