Cosmology and Fundamental Physics from High Precision CMB Lensing Science

关于我们的宇宙，最令人震惊的事实之一是，它的大部分内容都是不可见的。我们宇宙中超过80%的物质不是由原子组成的，而是由不可见的暗物质组成的，它们分布在一个巨大的暗物质网络中，构成所有可见物体的基础。这种暗物质分布的形式编码了关于我们宇宙的内容、起源和演化的丰富信息。我们如何能够看到这种看不见的暗物质结构？虽然暗物质不直接发射或散射光，但它施加的引力使我们能够间接观察到它的存在：一团暗物质通过引力吸引经过的光线，使它们的路径偏转，并使后面的一切看起来都被放大了。对这种引力透镜效应的观测使我们能够推断暗物质的存在。为了绘制出物质分布图，我们可以在最遥远的光源中寻找微妙的透镜特征：热大爆炸的余辉，宇宙微波背景辐射（CMB）。这种CMB辐射在到达我们的望远镜之前已经穿过了整个暗物质的宇宙网络。通过在这种CMB光中找到透镜特征，我们可以重建投射在整个可观测宇宙中的物质分布图。在过去的工作中，我首次测量了这种CMB透镜效应。现在，新的实验将首次提供极高质量的CMB数据，这对于暗物质分布的高精度透镜测量具有巨大的潜力。然而，透镜特征比CMB的平均亮度小十万倍以上，因此在这种精度水平下，从噪声数据中可靠地测量它们可能具有挑战性。我的研究计划将涉及理论，模拟，统计方法和数据分析，这将使这种强大的透镜测量工作。通过分析即将到来的CMB巡天（AdvancedACT和Simons Array）的数据，我将以前所未有的精度提取透镜信号，并构建一张高分辨率的宇宙大部分暗物质分布图。这种高精度的CMB透镜质量图将是新物理学的有力探测器。例如，宇宙暗物质分布的形式受到中微子存在的影响，中微子是一种性质知之甚少的粒子。虽然中微子占已知基本粒子的四分之一，但它们的质量完全未知。暗物质分布的形状取决于这些粒子的质量，因为中微子的质量越大，它们的运动就越能消除宇宙暗物质分布中的细微特征。有了精确的CMB透镜图，我将测量物质分布的详细形状，从而确定中微子的质量。这将阐明这种神秘粒子的性质，并深入了解其质量的物理来源。对CMB透镜信号的精确了解也将使我们能够更多地了解宇宙的起源。我们关于宇宙起源的主要理论是暴胀--一种导致宇宙最初以指数速度膨胀的机制。然而，这一机制尚未得到明确的确立，关于它发生的能量也知之甚少。虽然CMB极化中的某种特征模式（B模式）将是暴胀的决定性证据，并将决定其能量，但目前对这种暴胀模式的测量是有限的，因为暴胀效应可能与透镜效应相混淆。然而，如果我们可以直接测量CMB透镜信号，我们就可以从暴胀效应中分离出透镜效应。有了我构建的精确透镜映射，我将能够对暴胀和宇宙的起源进行更有力的约束。

One of the most striking facts about our universe is that most of its contents are invisible. More than 80% of the matter in our universe is not made of atoms, but instead of invisible dark matter, distributed in an enormous filamentary dark matter network that underlies all visible objects. The form of this dark matter distribution encodes a wealth of information about the contents, origin, and evolution of our universe.How can we see such invisible dark matter structures? Though dark matter does not emit or scatter light directly, it exerts a gravitational pull that allows us to observe its presence indirectly: a clump of dark matter gravitationally attracts rays of light that are passing by, deflecting their paths and causing everything that lies behind to appear magnified. Observation of this gravitational lensing effect allows us to infer the presence of dark matter. To map out the matter distribution, we can search for subtle lensing features in the most distant source of light: the afterglow of the hot big bang, the cosmic microwave background radiation (CMB). This CMB radiation has traversed the entire cosmic web of dark matter before reaching our telescopes. By finding lensing features in this CMB light, we can reconstruct maps of the matter distribution projected across the entire observable universe.In past work, I made some of the first measurements of this CMB lensing effect. Now, for the first time, new experiments will provide CMB data of extremely high quality, which have immense potential for high-precision lensing measurements of the dark matter distribution. However, the lensing features are more than a hundred thousand times smaller than the mean brightness of the CMB, so measuring them reliably from noisy data can be challenging at this level of precision. My research program will involve work in theory, simulation, statistical methods and data analysis that will enable such powerful lensing measurements. Analyzing data from upcoming CMB surveys known as AdvancedACT and Simons Array, I will extract the lensing signal at unprecedented precision and construct a high-resolution map of the dark matter distribution across much of the universe.Such highly precise CMB lensing mass maps will be powerful probes of new physics. For example, the form of the cosmic dark matter distribution is affected by the presence of neutrinos, a type of particle with poorly understood properties. Though neutrinos make up a quarter of the known elementary particles, their masses are completely unknown. The shape of the distribution of dark matter depends on the masses of these particles, because the more massive neutrinos are, the more their motions smooth out fine features in the cosmic dark matter distribution. With precise CMB lensing maps, I will measure the detailed shape of the matter distribution and hence determine how massive neutrinos are. This will elucidate the properties of this mysterious type of particle and give insight into the physical origin of their masses.Precise knowledge of the CMB lensing signal will also allow us to learn more about the beginning of the universe. Our leading theory for the cosmic origin is inflation -- a mechanism that causes the universe to initially expand exponentially fast. However, this mechanism has not been definitively established, and little is known about the energy with which it took place. While a certain characteristic pattern (B-modes) in the polarization of the CMB would be definitive evidence for inflation and would determine its energy, measurements of this inflationary pattern are currently limited because inflationary effects can be confused with similar effects from lensing. However, if we can directly measure the CMB lensing signal, we can disentangle the lensing effects from the inflationary effects. With the precise lensing maps I construct, I will thus enable more powerful constraints on inflation and the beginning of our universe.