A Precision Measurement of the Polarization of the 2.7K Cosmic Microwave Background Radiation

最近对2.7K宇宙微波背景辐射（CMBR）的光谱和空间各向异性的测量，极大地提高了我们对早期宇宙的认识。这种辐射的第三个特征，即它的极化，还没有被精确地测量出来。线偏振的振幅及其角相干长度对各向异性的来源（密度扰动或引力波）和宇宙的电离历史都极为敏感。预测极化幅值为COBE/DMR各向异性信号在7或T/T110-6时的10%。这笔拨款将支持进行针对这个角度尺度和更小尺度优化的首次测量。它将使用比以前的偏振实验灵敏度高100倍的新接收器技术，以及一种新的仪器设计。预计将达到比这个比额表目前的上限低100倍左右。改进的上限或极化检测将有助于：确定大尺度的各向异性是由密度扰动还是由引力波产生的确定复合是否是瞬时的确定再电离的红移研究各向异性与极化的相关性约束CMBR可能的极化源，如轴子、宇宙弦和织构。首先是大角度尺度(7)，然后是小尺度(1)。目前正在建造两种专门针对这两种测量方法进行优化的新型偏振计。它们将在两种不同的毫米波波长下工作，以抑制同步辐射的前景发射，并具有严格控制的系统效应和达到预期信号水平所需的高灵敏度。＊＊＊

ABSTRACT 9318727 Timbie Recent measurements of the spectrum and the spatial anisotropy of the 2.7K Cosmic Microwave Background Radiation (CMBR) have dramatically improved our understanding of the early universe. The third characteristic of this radiation, its polarization, has not been measured as precisely. The amplitude of the linear polarization and its angular coherence length are extremely sensitive to both the source of anisotropy (density perturbations or gravitational waves) and the ionization history of the universe. The predicted polarization amplitude is 10% of the size of the COBE/DMR anisotropy signals at 7, or T/T110-6. This grant will support o perform the first measurements optimized for this angular scale and smaller. It will use new receiver technology with 100 times more sensitivity than previous polarization experiments, as well as a novel instrument design. It is expected to reach a factor of about 100 below present upper limits at this scale. An improved upper limit, or detection of polarization will help to: determine whether the large-scale anisotrophies were generated by density perturbations or by gravitational waves determine if recombination was instantaneous determine the redshift of reionization study the correlation of anisotropy with polarization constrain possible alternative sources of polarization of the CMBR such as axions, cosmic strings, and textures The project will measure CMBR polarization, first at large angular scales (7) and later at smaller scales (1). Two novel polarimeters optimized specifically for both measurements are being constructed. They will operate at two different millimeter wavelengths to reject foreground emission from synchrotron radiation and feature strictly- controlled systematic effects and the high sensitivity required to reach the expected signal level. ***