Constraining gravity with cosmology

最近的过去见证了宇宙学的巨大成功，以极其精确的方式限制了宇宙的结构、内容和进化。因此，目前宇宙学的一个重点是了解这种进化背后的因素，确定宇宙在早期和晚期加速膨胀背后的基本物理学，以及暗能量和暗物质的本质。这项事业的关键是彻底了解重力本身——这是自然界已知力中最不为人所知的。具体来说，这涉及到测试、约束（以及潜在地检测偏离）我们目前最好的工作理论：广义相对论。随着新的观测窗口的出现（例如引力波的第一次探测）以及其他已建立的重力探测器（例如宇宙微波背景的观测），我们目前拥有显著且不断增长的数据量，使我们能够精确地测量引力现象。同时，最近在理解一致的引力理论必须具备的特征方面的理论进展，使我们能够对引力的行为以及它如何与宇宙中的物质相互作用施加额外的严格限制。总的来说，这意味着我们目前拥有前所未有的强大仪器，可以精确地识别和约束引力的本质。考虑到它们来自不同的物理领域，这些仪器到目前为止还没有被联合使用过，但它们在性质上的不同操作方式意味着它们实际上是理想的互补，以各种不同的方式测试和探测重力。因此，本研究计划旨在充分利用这种互补性，整合从数据驱动的数值代码的开发到高能粒子物理理论边界的实现等方法，以获得迄今为止最系统和最严格的重力边界。通过这种方式，我们将能够彻底探索重力的本质，在这个过程中测试它的几个基本特性。

The recent past has witnessed phenomenal successes in cosmology, constraining the structure, content and evolution of the Universe with tremendous accuracy. Consequently, a current focus of cosmology is to gain an understanding of the agents behind this evolution, identifying the fundamental physics behind the accelerated expansion of the Universe at early and late times and the nature of dark energy and dark matter. Key to this enterprise is thoroughly understanding gravity itself - the least well-understood of the known forces in nature. Specifically, this involves testing, constraining (and potentially detecting deviations from) our current best working theory: General Relativity. With the emergence of new observational windows (e.g. the first detections of gravitational waves) in addition to other well-established probes of gravity (e.g. observations of the cosmic microwave background), we presently have a remarkable and continuously growing amount of data allowing us to precisely measure gravitational phenomena. Simultaneously, recent theoretical advances in understanding what features a consistent theory of gravity must possess, enable us to impose additional strong restrictions on how gravity can behave and and how it interacts with matter in the universe. Altogether this means we currently have at our disposal an unprecedented amount of powerful instruments to precisely identify and constrain the nature of gravity. Given the different areas of physics they originate from, these instruments have not been used jointly so far, yet the qualitatively different ways in which they operate means they in fact ideally complement one another, testing and probing gravity in a variety of different ways. This research program therefore aims to take full advantage of this complementarity, integrating methods ranging from the development of data-driven numerical codes to the implementation of theoretical bounds from high-energy particle physics in order to obtain the most systematic and tight bounds on gravity yet. In this way, we will be able to thoroughly probe the nature of gravity, testing several of its fundamental properties in the process.