Detecting B-mode signals in the early Universe

主讲人 (Speaker): 

冯畅

主讲人单位 (Speaker's Institute): 

伊利诺伊大学香槟分校物理系

邀请人 (Invited by): 

黄志琦

时间 (Time): 

星期四, 2019/03/28 - 11:00 to 12:00

地点 (Location): 

珠海校区海滨红楼17栋107 (Rm 107, Red House 17)

摘要 (Abstract): 

早期宇宙的研究对一些基础物理问题有重要的意义。宇宙微波背景辐射，这种由大爆炸遗留下来的辐射，是探测早期宇宙的一个主要方式。微波背景的光子是具有偏振属性的，并且天空中不同方向上的偏振扰动可以被分解为类电场(E)和类磁场(B)模式。对B模式的探测现在成为了微波背景实验的一个主要目标。因为由早期宇宙的量子扰动产生的原初引力波被认为是产生这种大尺度B模式信号的原因。然而，其它的机制包括大尺度结构，原初磁场，和原初恒星与星系均能在不同尺度上产生B模式信号。从微波背景，红外背景，以及21厘米线的观测上，这些机制能够被有效地限定，因而在不远的将来，原初引力波有望被更精确地探测到。从另一方面，这些机制有助于搞清楚宇称破坏相关的物理，暗物质，和再电离阶段。在这个报告中，我将系统地介绍这些B模式机制的最新研究，并展示一些通过最新的数据和分析技术得到的新结果。

        Studies of the early Universe are very important to some fundamental problems in physics. The Cosmic Microwave Background (CMB) radiation, which is a relic radiation from the Big Bang, is a major probe to the early Universe. The CMB photons are polarized due to photon-electron scattering in the early Universe and the polarization fluctuations at different directions in the sky can be decomposed into electric- (E-) and magnetic-like (B-) modes. The B-mode signature has been a main target for CMB experiments because primordial gravitational waves, that are powered by quantum fluctuations in the very early Universe, are believed to give rise to the large-scale B-mode signal, however, other sources including large scale structure, primordial magnetic fields, and primordial stars and galaxies, can also produce B-mode signals at different angular scales. These sources can be effectively constrained by measurements at microwave, infrared wavelengths and 21 cm lines, so the primordial gravitational waves would be more precisely detected in the future. On the other hand, these sources also shed light on parity-violating physics, dark matter and epoch of reionization. In this talk, I will systematically introduce recent studies of these B-mode sources and show latest measurements with new data and novel analysis techniques.

主讲人简介 (Speaker's CV): 

Dr. Chang Feng obtained his Ph.D degree in Physics from the University of California San Diego in 2014. Then he moved to the University of California Irvine as a postdoctoral research associate. After that, he has been working at the University of Illinois at Urbana-Champaign as a postdoctoral research associate in the physics department.