String Cosmology: New Tools to connect String Theory with Cosmological Observations

弦宇宙学：连接弦理论与宇宙学观测的新工具

• 批准号: ST/H005498/2
• 负责人: Gianmassimo Tasinato
• 金额: $ 14.11万
• 依托单位: Swansea University
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FH005498%2F2
• 关键词: String; Cosmology; New; Tools; connect

Cosmology studies the origin of the Universe, and the main features of its evolution until today. The Universe expansion is mainly controlled by gravity, the force described by Einstein's General Relativity. This theory is extremely successful for describing gravitational phenomena that occur at large distances. However, when attempting to describe phenomena occurring at small scales, General Relativity apparently fails. Indeed, the best theories we have to describe short distance physics are based on Quantum Mechanics. But its principles lead to inconsistent results, when applied to gravitational phenomena following the rules of General Relativity. This problem is relevant for Cosmology, when trying to investigate epochs in which the Universe was very young, and then very small, in which quantum mechanical effects are important. For example, in the early epochs of our Universe, it is believed that cosmological expansion has experienced a phase of extremely fast acceleration, called Inflation. During this epoch, quantum effects are decisive to produce small inhomogeneities in the structure of the space-time, that seed large scale structures in the subsequent evolution of the Universe. The aim of consistently conjugate General Relativity with Quantum Mechanics is the main goal that motivated the development of String Theory. This theory introduces very unusual concepts: its consistency requires that our Universe has six dimensions more than the observed ones, that are wrapped on a small space, and unobservable by everyday experience. Also, it predicts the existence of membrane objects, fluctuating in a higher dimensional background, where the particle constituting our Universe can be localized. In order to check these beautiful ideas, however, we need to probe phenomena happening at extremely small scales. I find all these ideas extremely exciting, so I decided to study the relation between string theory and cosmology, with the main aim to find new ways to test string theory by cosmological observations. As explained before, phenomena occurring at early epochs, when the Universe was extremely small, are affected by short distance physics, and then possibly by String Theory. Inflation is the most important example: it is a process that leaves clear imprints in the pattern of the observed CMB radiation, and provides initial conditions affecting the subsequent evolution of the Universe. For these reasons part of my research is devoted to study models of inflation in String Theory. They can have peculiar properties, since they use many of the ingredients that the theory offers. The study of string models of inflation, then, offers unique opportunities to reveal effects that are characteristic of String Theory, and allows to test its ideas by means of cosmological observations. More specifically, the main objectives of my research activity can by summarized in the following. First, I plan to develop the theoretical tools allowing to compare observational results with string motivated cosmological models. This is a broad subject that requires the elaboration of existing techniques aimed to analyze the evolution of cosmological fluctuations, in order to apply them to string motivated cosmological models. Then, I will try to individuate the most promising cosmological models, based on string theory, that offer the best opportunities for being testable with future cosmological observations. Once this has been done, I will try to elaborate those models, in order to render them fully satisfactory from a theoretical point of view, and study in detail their predictions for cosmological quantities that will be tested by observations.

宇宙学研究宇宙的起源，以及迄今为止宇宙演化的主要特征。宇宙膨胀主要受引力控制，即爱因斯坦广义相对论所描述的力。这个理论非常成功地描述了发生在远距离的引力现象。然而，当试图描述在小尺度上发生的现象时，广义相对论显然是失败的。事实上，我们所拥有的描述短距离物理的最佳理论是基于量子力学的。但是，当按照广义相对论的规则应用于引力现象时，它的原理导致了不一致的结果。这个问题与宇宙学有关，当试图研究宇宙非常年轻，然后非常小的时代时，量子力学效应很重要。例如，在我们宇宙的早期，人们认为宇宙膨胀经历了一个极快的加速阶段，称为暴胀。在这个时代，量子效应在时空结构中产生微小的非均质性是决定性的，而这些非均质性在随后的宇宙演化中为大规模结构埋下了种子。将广义相对论与量子力学相结合是弦理论发展的主要目标。这个理论引入了非常不寻常的概念：它的一致性要求我们的宇宙比观测到的宇宙多六个维度，这些维度被包裹在一个小空间里，日常经验无法观察到。此外，它还预测了膜物体的存在，在更高维度的背景中波动，在那里构成我们宇宙的粒子可以被定位。然而，为了验证这些美好的想法，我们需要探索在极小尺度上发生的现象。我发现所有这些想法都非常令人兴奋，所以我决定研究弦理论和宇宙学之间的关系，主要目的是找到通过宇宙学观测来检验弦理论的新方法。如前所述，发生在早期时代的现象，当时宇宙非常小，受短距离物理学的影响，然后可能受弦理论的影响。暴胀是最重要的例子：它是一个在观测到的CMB辐射模式中留下清晰印记的过程，并为影响宇宙随后的演化提供了初始条件。由于这些原因，我的部分研究致力于研究弦理论中的膨胀模型。它们可以具有特殊的性质，因为它们使用了理论提供的许多成分。因此，对膨胀弦模型的研究提供了独特的机会来揭示弦理论的特征效应，并允许通过宇宙学观测来检验它的观点。更具体地说，我的研究活动的主要目标可以概括如下。首先，我计划开发理论工具，以便将观测结果与弦驱动的宇宙学模型进行比较。这是一个广泛的主题，需要详细阐述旨在分析宇宙涨落演化的现有技术，以便将它们应用于弦驱动的宇宙模型。然后，我将尝试个性化最有希望的宇宙学模型，这些模型基于弦理论，为未来的宇宙学观测提供了最好的测试机会。一旦这项工作完成，我将尝试详细阐述这些模型，以便从理论的角度使它们完全令人满意，并详细研究它们对宇宙量的预测，这些预测将通过观测来检验。