Cosmological constraints on scalar filed as a candidate of dark energy

本研究从精粹模型（自相互作用标量场模型）和高维宇宙学的角度分析了暗物质的起源和高维时空的可能性。Randall-Sundrum模型是目前提出的各种高维宇宙论中最有趣的模型之一。在该模型中，我们的宇宙被描述为出现在五维时空中的四维膜（膜）。通过三个重要观测（大爆炸核合成、宇宙微波背景、IA型超新星观测）对这些模型的有效性进行了分析。主要结论总结如下：在高维时空中由引力产生的暗辐射的数量受到了三次观测的限制。假设暗物质是可以被描述为五维标量场的大质量粒子，我们证明了暗物质只在有限的时间内被困在我们的膜上。利用2的结果，我们提出了一个“消失的暗物质”模型，在这个模型中，被困在膜上的暗物质在有限的时间内衰变到高维时空中。衰变时间由三个观测值估计。生命的时间被发现在宇宙年龄附近。我们在Randall-Sundrum模型中推导出牛顿定律，其中模型参数被调整为具有正的宇宙常数。在小距离处的结果形式不同于平方反比定律。

This research analyzed the origin of the dark matter and the possibility of higher dimensional spacetime from the viewpoint of the Quintessence model (self-interacting scalar field model) and the higher-dimensional cosmology. The Randall-Sundrum model is one of the most interesting models among various types of higher-dimensional cosmologies proposed so far. In the model, our universe is described as a membrane (brane) of four dimensions which appears in the five dimensional spacetime. The validity of these models was analyzed by using three important observations (big bang nucleosynthesis, cosmic microwave background, type IA supernova observation). A main conclusion is summarized in the following.1.The amount of darkness radiation, which is generated by the gravity in the higher dimensional spacetime, was constrained by the three observations.2.Assuming the dark matter is the massive particle which can be described as the five-dimensional scalar field, we showed that the dark matter is trapped on our brane only during a limited time.3.Using the result of 2,we proposed a model called "disappearing dark matter", in which the dark matter trapped on the brane decays into the higher-dimensional spacetime in a finite time. The decaying time was estimated by the three observations. The life time was found to be around the cosmic age.4.We derived Newton's law in the Randall-Sundrum model in which the model parameter is tuned to have the positive cosmological constant. The resultant form is different from the inverse square law at small distance.