【作者】 郑伟；

【导师】 陆埮；

【作者基本信息】 南京大学 ， 物理学， 2014， 博士

【摘要】 大爆炸(Big Bang)宇宙学被认为有三大实验基石：Hubble膨胀,原初核合成和宇宙微波背景辐射(CMB)。在这三大实验事实之上,基于宇宙学原理和广义相对论,标准宇宙学模型便基本建立了起来。一方面,它给出了一个随时间演化的均匀各向同性的背景宇宙,背景宇宙的演化由尺度因子来描述,尺度因子的演化遵守Friedmann方程。另一方面,现代宇宙学认为真实的宇宙是一个存在扰动的宇宙：宇宙的时空存在微小的不均匀性,宇宙中的物质分布存在结团性。一个在背景之上存在微小涨落的宇宙可以通过线性扰动理论来描述。今天宇宙中如此多复杂结构的存在都是原初宇宙的密度扰动由于引力不稳定性演化而形成的,而原初宇宙的密度扰动的产生可以用暴涨理论给予解释。暴涨理论认为,极早期的宇宙是高度的均匀各向同性的。在能标大约1015GeV时候,宇宙经历了一次十分短暂的加速膨胀过程。在此期问的产生的微观尺度上真空量子涨落被迅速拉出视界,从而在宏观尺度上冻结成为了经典的原初扰动。随着观测设备的改善和观测技术的提高,目前宇宙学的研究已经进入了精确时代。精确时代的宇宙学研究体现在能够利用较精确的宇宙学观测数据实现对宇宙学模型参数的较精确测量。在这个阶段,观测宇宙学取得了一系列进展。其中十分有意义的有两件事：a.1998年利用较远的Ia型超新星数据(SNIa)确定了宇宙在加速膨胀,这暗示了暗能量的存在；b. COBE之后的两代CMB各向异性测量卫星WMAP和Planck精确的给出了宇宙背景微波辐射涨落的角功率谱,这使得我们可以细致的对宇宙早期的物理过程进行研究。目前来自宇宙微波背景辐射,重子声波振荡(BAO),Ia型超新星等传统宇宙探针的数据仍然支持宇宙学常数冷暗物质模型(ACDM)。在这个模型之下,宇宙是空间平坦的,具有近标度不变的原初标量扰动谱,宇宙的总能量密度中其中有约70%是宇宙学常数(A)暗能量,近25%是冷暗物质(CDM),只有约5%是粒子物理标准模型(SM)下的物质。当然,传统数据也同样支持一些超出ACDM的模型,这些模型在ACDM模型的基础上引入了一些额外的参数。但是,由于在传统数据之下宇宙学参数之间存在着各种简并,使得即使一些精度较高的数据也无法给这些模型中的一些关键参数以很好的限制。所以我们考虑采用一种较新的宇宙学探针—对Hubble参量的直接测量。Hubble参量反映了宇宙膨胀的历史,它与宇宙中各个组分的信息联系在一起,我们期待可以用它的观测数据来打破简并,并改善限制。我们在传统观测数据的基础上加入哈勃参量的观测数据,对参数化的各种超出ACDM的扩展宇宙学模型进行了限制。结果显示,由于哈勃参量的数据可以给宇宙晚期的膨胀率提供额外的信息,所以当把不同红移的数据点包括进入分析之后,对打破某些宇宙学参数之间的简并起到了较大帮助,从而对这些参数给出了更好的限制；另外,由于一些拟合参数与Hubble常数Ho存在简并,所以Ho的直接测量值在数据分析中可以明显影响这些参数的中心值,并给以了比较好的限制,比如对有效中微子代数Ⅳeff来说就是这样。自从对Ia型超新星的观测发现宇宙加速膨胀以来,暗能量这个可能是驱动宇宙作加速膨胀的神秘的成份,一直就是当代宇宙学的热点话题。对暗能量的物理本质有各种各样的假设,比如真空能,各种标量场等等,但这些关于暗能量的物理解释中还没有一个有绝对的说服力。所以利用观测数据对参数化的暗能量模型的限制就显得很重要。对暗能量来说,状态方程(EoS)是描述它自身性质的关键参数,它决定了暗能量密度的演化规律。所以,我们采用了最新的观测数据对暗能量状态方程进行了研究：我们利用了来自Planck的CMB角功率谱数据,Pan-STARRS超新星样本以及BAO的观测数据,并采用了三种不同的暗能量状态方程的参数化方法：常数状态方程w,随时间演化的2-参数形式的状态方程(w(a)=w0+wa(1-a)),分bin的分段常数暗能量状态方程(bin-w).对bin-w的结果,我们还进行了主成分分析(PCA)来使得我们得到的EoS结果更加物理。结果显示,对于前两种参数化,拟合得到的状态方程分别在2σ和1σ的置信水平仍然是和ACDM自洽的；对于分bin的参数化,整体拟合的结果与ACDM符合的很好,但PCA处理得到的结果显示了EoS在某些红移bin上对伽=-1的轻微偏离。考虑到许多bin上的误差仍然比较大,故我们需要更多的数据做进一步的验证。更多还原

【Abstract】 The big bang cosmology is considered to have three observational pillars:Hub-ble expansion, primordial nucleosynthesis and cosmic microwave background(CMB). Basing on the three observational pillars, the standard cosmological model set up by using cosmological principle and general relativity. On the one hand, the standard cos-mological model gives a time-evolution universe which is homogeneous and isotropic. The evolution of the background universe is described by the scale factor, and the evo-lution of the scale factor obeys the Friedmann equation. On the other hand, the modern cosmology holds that the real universe is the one that has perturbation:the space and time of the universe is not perfectly homogeneous, and the clump exists in the distri-bution of matter in the universe. A universe that has tiny fluctuation can be described by the linear theory of cosmological perturbation. The existence of complex structure in the present universe is the result of the evolution of primordial density perturbation due to gravitational instability, and the origin of the primordial perturbation can be ex-plained by inflation theory. According to the inflation theory, the very early universe is highly homogeneous and isotropic. When the energy scale is about 1015GeV, the universe went through a very short process of accelerated expansion. The quantum fluctuation generated during this short time was quickly pulled out of Hubble horizon, and frozen into the classical primordial perturbation on the large scale.With the improvement of observation equipment and technology, now the study of cosmology has entered the precision time. Research on precise cosmology is embodied in the accurate measurement on cosmological parameters by using precise observation-al data. During this stage, the observational cosmology has made a series of progress. Two things are very significant:a. discovering the accelerating expansion of universe by using the data of distant la supernovae (SNIa) in 1998, which implies the existence of dark energy; b. WMAP and Planck, the satellites of two generation that measure the CMB anisotropy after COBE, have precisely given the angular power spectrum of CMB fluctuation, which allows us to carefully study the physical process of the early universe.The current data from traditional cosmological probes, such as CMB, BAO and SNIa, are still supports ACDM model. In the framework of this model, the universe is spatially flat, has a nearly scale-invariant spectrum of primordial scalar fluctuation-s, nearly 70% of the total energy density in the universe is cosmological constant(A) dark energy,25% of the total energy density in the universe is cold dark matter(CDM), and the SM matter only accounts for about 5%. On the other hand, traditional data also support some extended ACDM models, which introduced some extra parameters based on ACDM model. However, due to various degeneracies among these cosmo-logical parameters under the traditional data, even some data that has high precision cannot give very good constraints on some crucial parameters. So we consider a new kind of cosmological probe-the direct measurement on Hubble parameters. Hubble parameters reflect the expansion history of the universe, and it is related to the infor-mation of the various species in the universe, so we hope the observational data from it can help to break the degeneracies and improve the limits. We include the observation-al data from Hubble parameters into the traditional probes, and study the constraints on several extended ACDM models. The results shows it is very helpful to break de-generacies among some cosmological parameters when including the data at different redshift points into the analysis, since the Hubble parameters data could provide the ex-tra information of the expansion rate of universe at late times, thus we can obtain better constraints on these parameters. Additionally, The HST measurement on the Hubble constant, HST Ho prior, can obviously impact on the median values of parameters and also give good constraints on some of them, such as the effective number of neutrinos Neff, due to the degeneracies between these parameters and H0.Since the discovery of the accelerating expansion of the universe from the obser-vations of type la supernovae, dark energy, the mysterious component in our universe which drives the acceleration, remains the hot topic in modern cosmology. There are a variety of assumptions about the nature of dark energy, such as the vacuum energy, and some kinds of scalar field. But none of these physical explanations is compelling. So the determination on the parameterized dark energy model from observational data is very important. For the dark energy, equation of state (EoS) is the key parameter to describe its properties, which determines the dark energy density evolution. Therefore, we adopt the latest observations to study the EoS:we make use of observational data combination of angular power spectrum data from Planck, Pan-STARRS SNIa sample and BAO, and have performed 3 different data fitting by adopting a constant EoS, a time-evolving EoS(w(a)=w0+wa(1-a)) with 2-parameter form and EoS of piece-wise constant bins (bin-w). For the result of bin-w, we do the method of PCA to make our EoS more physical. The result shows that, for the first two forms of param-eterization, the EoS is still consistent with ACDM at 2σ and 1σ respectively; for the bin-w case, the global fitting results are well consistent with ACDM, but EoS may deviate from-1 slightly in some of the redshifts bins after the the model-independent PCA analysis. Considering the relatively larger errors in many bins, we still need more data to confirm this point.更多还原