Precision cosmology from early and late-time surveys.

宇宙学的探索主要是出于好奇，想知道事物是如何在时间中开始和演化的，是哪个特定的过程导致了我们在天空中看到的物体（例如，星系和星系团），它们来自哪里，为什么它们正在远离我们。早期宇宙物理学的一个关键方面是宇宙微波背景辐射（CMB）温度波动和极化的理论和观测。利用CMB来研究宇宙的粒子和能量含量以及它的演化是现代宇宙学的一个显著成功。CMB是我们能在宇宙中观测到的最古老的光。它诞生于宇宙大爆炸后几秒钟的早期宇宙，并在宇宙的高温将光与其他粒子耦合在一起的原始“宇宙汤”中热化。然后，当宇宙冷却下来，第一批轻元素开始形成（例如氢和氦）时，它解耦并释放出来，使CMB光子自由地逃逸。然后，CMB为我们提供了透明宇宙的快照和独特视图。它可以自由地从解耦时刻传播到今天，它以微弱的微波辐射的形式到达我们这里。它的传播方式和统计特性告诉我们早期宇宙的物理学（从解耦中回顾过去），并描述了它的粒子/能量含量和进化（从解耦中展望未来）。CMB温度变化的统计数据现在已经在广泛的尺度范围内以极高的精度测量，从而导致宇宙学的一致性标准模型。然而，今天出现的标准宇宙学模型依赖于观测证据，这些证据表明成分和过程具有未知的理论解释。我们测量出95%的宇宙是由“暗”成分主导的，但我们还不知道它们的本质是什么。我们称“暗物质”为负责星系形成的成分，称“暗能量”为反对重力并推动宇宙加速膨胀的力量，所有这些都假设重力定律在所有尺度上都是正确的。我们还需要援引宇宙大爆炸后不到一秒的超光速膨胀来解释宇宙在宇宙尺度上的均匀性及其平坦性。在过去的十年中，CMB数据已经成为解决这些开放理论问题的最具竞争力和最诱人的信息来源。我的项目依赖于在未来十年补充现有数据的两种观测：改进的CMB极化测量和在大宇宙时代的最大物理尺度（如星系团、空洞、细丝、气泡）上的星系统计和分布测量。在2013年底和2014年初，地面实验对CMB偏振的新测量开启了CMB物理学的新时代。CMB的极化将使我们了解早期宇宙的短暂膨胀阶段（称为宇宙膨胀），探测无法在实验室中测试的高能量尺度，并将绘制引力势场，定义宇宙的几何形状、演化和内容。宇宙微波背景的极化对于研究至今仍未测量到的原始中微子的质量特别有效。通过星系调查，目前和未来对宇宙大尺度结构的探测，将有效地描述黑暗区域的特征，并在宇宙尺度上测试引力定律。CMB和星系调查的结合将增加宇宙学重建的保真度，减少系统学并探测许多宇宙时代（CMB给我们一个约40万年前的宇宙快照，而星系调查则探测过去100亿年）。

The cosmological quest is mainly fed by the curiosity to know how things started and evolved in time, which particular process led to the objects we see in the sky (e.g., galaxies and clusters of galaxies), where they come from and why they are moving away from us. A key aspect of physics of the early Universe is the theory and the observation of the cosmic microwave background radiation (CMB) temperature fluctuations and polarisation. The use of the CMB to study the particle and energy content of the Universe as well as its evolution is a remarkable success of modern cosmology. The CMB is the most ancient light we can observe in the Universe. It was born in the early Universe a few seconds after the Big Bang and thermalised in the primordial 'cosmic soup' where the high Universe temperature coupled light together with other particles. It then decoupled and was released when the Universe cooled down and the first light elements started to form (e.g., hydrogen and helium), leaving CMB photons free to escape. The CMB then provides us with a snapshot and unique view of the transparent Universe. It has been free to travel from the decoupling moment to today and it reaches us as a faint radiation with microwave wavelengths. The way it propagates and its statistical properties inform us about the physics of the early Universe (looking back in time from decoupling) and describes its particle/energy content and evolution (looking forward in time from decoupling). The statistics of the CMB temperature variations have now been measured with extreme precision over a broad range of scales, leading to a concordance standard model of cosmology. However, the standard cosmological model arising today relies on observational evidence for components and processes with unknown theoretical interpretation. We measure that 95% of the Universe is dominated by 'dark' components but we don't know yet what their nature is. We call 'dark matter' the component responsible for the galaxies formation and 'dark energy' the force opposing gravity and driving the Universe in an accelerating expansion, all this assuming that the laws of gravity are correct on all scales. We also need to invoke a super-luminal expansion in the first fraction of a second after the Big Bang to account for the homogeneity of the Universe on cosmic scales and its flatness. In the last ten years CMB data has become the most competitive and tantalising source of information to address these open theoretical issues. My project relies on two kinds of observations complementing current data in the next decade: improved measurement of CMB polarisation and the measurement of galaxies statistics and distribution on the largest physical scales (e.g., galaxy clusters, voids, filaments, bubbles) over a broad cosmic epoch. At the end of 2013 and early 2014 the new measurements of CMB polarisation from gound-based experiments have kicked off a new era in CMB physics. CMB polarisation will inform our understanding of the brief expansion phase of the early Universe (called cosmic inflation), probing high energy scales not testable in laboratories, and will map the gravitational potential field defining the geometry, evolution and content of the Universe. CMB polarisation is particularly effective for studying the masses of primordial neutrinos, still unmeasured today. Current and future probes of the Universe large-scale structure, via galaxy surveys, will be instead effective in characterising the dark sector and testing the gravity laws on cosmic scales. The combination of CMB and galaxy surveys will increase the fidelity of the cosmological reconstructions, reducing systematics and probing many cosmic epochs (the CMB gives us a snapshot of a ~400,000 years old Universe while galaxy surveys probe the last 10 billion years).