Testing Fundamental Physics with B-modes of Cosmic Microwave Background anisotropy

用宇宙微波背景各向异性的 B 模式测试基础物理

• 批准号: RGPIN-2020-05346
• 负责人: Frolov, Andrei
• 金额: $ 2.04万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=740523
• 关键词: Testing; Fundamental; Physics; modes; Cosmic

The origins of the universe we live in and the early epochs of its existence has always fascinated people. With discovery and observations of the cosmic microwave background, it is now possible to take a "photograph" of the universe when it was about 400,000 years old. While the picture starts as a visible light, universe expansion cools the light down and it reaches us in the form of the microwaves at the present day. Physics processes in the early universe get imprinted in spatial fluctuations of the intensity and polarization of the cosmic microwave radiation. We see primordial gravitational potential fluctuations as intensity and "straight" patterns in polarization, while primordial gravitational waves would look like "curly" patterns. These are known as B-modes, and we have not seen them yet. The goal of my research is to work on their detection. You do not get to see just cosmic microwave background, as a lot of astrophysical sources in our galaxy are also bright in these frequencies. Two of them are highly polarized - the thermal dust that aligns itself with galactic magnetic field, and the synchrotron radiation produced by charged particles as they rotate around in the magnetic field. They are much brighter than the signal we are looking for, but they can be distinguished from the cosmic microwave background by the colour of light they emit. It is a bit like trying to make out a Milky Way on a clear night in a city, being blinded by coloured lights all around you, except now it is the Milky Way that blinds us. It appears to be possible to characterize the dust and synchrotron polarization, and to try to remove it from the picture. Dust grains align themselves to magnetic field like countless compass needles, and it is possible to reconstruct the direction of the magnetic field in our galaxy from polarization of light they produce. This gives a smooth polarization fraction pattern on the sky sourced by large-scale magnetic field features around us, and once that is subtracted the remainder is quite random, and can be dealt with as the usual noise. Polarization fraction pattern of synchrotron traces similar features, but the physics is more complex, so it needs further investigation. I propose to study these two astrophysical foregrounds, and develop new methods to remove them using the knowledge we gained. With Simons Observatory being build, and proposed CMB-S4 we will have a very low noise picture of the microwave sky, and the ability to see primordial cosmic microwave background will depend on how well we could subtract the foregrounds. As a member of both collaborations, I work with my colleagues on modelling and data analysis. If we see primordial gravitational waves, it would be a big step forward in understanding the early universe, and fundamental physics driving it. It could be a "smoking gun" confirmation of inflation at high energy scales, or it could push the scale of inflation low, as string theory models tend to prefer.

我们生活的宇宙的起源和它存在的早期时代一直吸引着人们。随着宇宙微波背景辐射的发现和观测，现在可以拍摄宇宙大约40万年前的“照片”。虽然这幅图像开始时是可见光，但宇宙膨胀使光冷却下来，并以微波的形式到达我们今天。早期宇宙中的物理过程在宇宙微波辐射的强度和偏振的空间波动中留下了印记。我们看到原始引力势波动的强度和极化的“直”模式，而原始引力波看起来像“卷曲”模式。这些被称为B模式，我们还没有看到它们。我研究的目标是研究它们的发现。你不能只看到宇宙微波背景，因为我们银河系中的许多天体物理源在这些频率下也很明亮。其中两个是高度极化的-热尘埃与银河磁场对齐，以及带电粒子在磁场中旋转时产生的同步辐射。它们比我们正在寻找的信号要亮得多，但可以通过它们发出的光的颜色将它们与宇宙微波背景区分开来。这有点像在一个晴朗的夜晚，在一个城市里试图辨认出一条银河，被你周围的彩色灯光所蒙蔽，除了现在是银河使我们失明。它似乎是有可能的特点，尘埃和同步加速器偏振，并试图将其从图片中删除。尘埃颗粒就像无数的指南针一样与磁场对齐，并且有可能从它们产生的光的偏振中重建我们星系中磁场的方向。这就给出了一个平滑的极化分数模式，它来源于我们周围的大尺度磁场特征，一旦减去它，剩下的就很随机了，可以作为通常的噪声来处理。同步加速器的偏振态分布也具有类似的特征，但物理过程更为复杂，需要进一步研究。我建议研究这两个天体物理学前景，并开发新的方法来消除他们使用我们获得的知识。随着西蒙斯天文台的建设和CMB-S4的提出，我们将获得微波天空的非常低噪音的图像，而看到原始宇宙微波背景的能力将取决于我们减去前景的能力。作为这两个合作项目的成员，我与同事一起从事建模和数据分析工作。如果我们看到了原初引力波，那将是理解早期宇宙和驱动它的基础物理学的一大步。它可能是高能尺度下暴胀的“确凿证据”，也可能像弦论模型倾向于的那样，把暴胀的尺度推低。