WEKO3
アイテム
Cosmological tests of models for the accelerating universe in terms of inhomogeneities
https://ir.soken.ac.jp/records/4066
https://ir.soken.ac.jp/records/40669262ce35ad4140178e8c2404039a0db1
名前 / ファイル  ライセンス  アクション 

要旨・審査要旨 (332.7 kB)


本文 (1.2 MB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20131115  
タイトル  
タイトル  Cosmological tests of models for the accelerating universe in terms of inhomogeneities  
タイトル  
タイトル  Cosmological tests of models for the accelerating universe in terms of inhomogeneities  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
齋藤, 惠樹
× 齋藤, 惠樹 

フリガナ 
サイトウ, ケイキ
× サイトウ, ケイキ 

著者 
SAITO, Keiki
× SAITO, Keiki 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第1589号  
研究科  
値  高エネルギー加速器科学研究科  
専攻  
値  14 素粒子原子核専攻  
学位授与年月日  
学位授与年月日  20130322  
学位授与年度  
値  2012  
要旨  
内容記述タイプ  Other  
内容記述  We study cosmological tests of models that can explain the apparent accelerated expansion of the present universe in terms of inhomogeneities. There are a number of models, such as dark energy models, modified matter models, modified gravity models, local void models, backreaction models, etc., and these models have to be tested by various observations other than the distanceredshift relation of type Ia supernova. Therefore, in this thesis, we provide methods of testing these models by particularly focusing on inhomogeneities of the universe, because, practically, our universe is inhomogeneous. First, we consider the effective gravitational stressenergy tensor for shortwavelength perturbations in modified gravity theories. In general relativity, a consistent expansion scheme for shortwavelength perturbations and the corresponding effective stressenergy tensor were largely developed by Isaacson, in which the small parameter, say ϵ, corresponds to the amplitude and at the same time the wavelength of perturbations. Isaacson’s expansion scheme is called the high frequency limit or the shortwavelength approximation. If the effective stressenergy tensor had a term proportional to the background spacetime metric, then it would correspond to adding a cosmological constant to the effective Einstein equations for the background metric, thereby explaining possible origin of dark energy from local inhomogeneities. It has been shown, however, that this effective gravitational stressenergy tensor is traceless and satisfies the weak energy condition, i.e. acts like radiation, and thus cannot provide any effects that imitate dark energy in general relativity. However, it is far from obvious if this traceless property of the effective gravitational stressenergy tensor is a nature specific only to the general relativity or is rather a generic property that can hold also in other types of gravity theories. The purpose of the first test is to address this question in a simple, concrete model in the cosmological context. Since f(R) gravity contains higher order derivative terms, one can anticipate the effective gravitational stressenergy tensor to be generally modified in the high frequency limit. Our analysis can be performed, in principle, either (i) by first translating a given f(R) gravity into the corresponding scalartensor theory and then inspecting the stressenergy tensor for the scalar field ϕ, or (ii) by directly dealing with metric perturbations of f(R) gravity. We may expect that the former approach is sufficient for our present purpose and much easier than the latter metric approach, as we have to deal with metric perturbations of complicated combinations of the curvature tensors in the latter case. Nevertheless we will take the both approaches. In fact, in the metric approach, by directly taking up perturbations of the scalar curvature, the Ricci tensor and the Riemann tensor involved in a given f(R) theory, we can learn how to generalize our present analysis of a specific class of f(R) gravity to analyses of other, different types of modified gravity theories that cannot even be translated into a scalartensor theory, such as the GaussBonnet gravity. Then, we will make sure that the effective stressenergy tensor in BransDicke theory is consistent with that in our f(R) gravity. Second, we discuss temperature anisotropies of cosmic microwave background (CMB) in local void models. Furthermore, those in the local void model and in the ΛLemaitreTolmanBondi (ΛLTB) spacetime are shown as a particular case. In order to justify the local void model as a viable alternative to the standard ΛCDM model, we have to test this model by various observations other than the SN Ia distanceredshift relation. Most of previous analyses were performed for various types of local void models by using numerical methods, and they do not seem to be straightforward to compare analyses for each different model so as to have a coherent understanding of the results. In order to have general consequences of the local void model and systematically examine its viability, it is desirable to develop some general, analytic methods that can apply, independently of the details of each specific model. The purpose of the second test is to derive the analytic formulae for the dipole and quadrupole of the CMB anisotropy in general spherically symmetric spacetimes, including the ΛLTB spacetime, and to give constraints on the local void model. Instead, we will exploit the key requirement of the local void model that we, observers, are restricted to be around very near the center of the spherical symmetry: Namely, we first note that the small distance between the symmetry center and an offcenter observer gives rise to a corresponding deviation in the photon distribution function. Then, by taking ‘Taylorexpansions’ of the photon distribution function at the center with respect to the deviation, we can read off the CMB temperature anisotropy caused by the deviation in the photon distribution function. By doing so, we can, in principle, construct the lth order multiple moment of the CMB temperature anisotropy from the (up to) lth order expansion coefficients, with the help of the background null geodesic equations and the Boltzmann equation. We will do so for the first and secondorder expansions to find the CMB dipole and quadrupole moments. We also provide the concrete expression of the corresponding formulae for the local void model. Our formulae are then checked to be consistent with the numerical analyses of the CMB temperature anisotropy in the local void model, previously made by Alnes and Amarzguioui. We apply our formulae to place the constraint on the distance between an observer and the symmetry center of the void, by using the latest Wilkinson Microwave Anisotropy Probe (WMAP) data, thereby updating the results of the previous analyses. 

所蔵  
値  有 