Background Imaging of Cosmic Extragalactic Polarization (BICEP): An Experimental Probe of Inflation

宇宙微波背景辐射（CMB）提供了三个强有力的间接证据，证明可见宇宙是由微小空间的超光速膨胀产生的：视界的近各向同性，空间的平坦性，以及早期宇宙中声学振荡的相位同步性。为了更好地理解宇宙的起源，需要直接探索暴胀时期。最有希望的通货膨胀探针是GWB在CMB极化上留下的独特印记。这个信号的振幅取决于暴胀的能量尺度。如果能量标度是大统一理论（GUT）的典型标度（10^15 3 x 10^16 GeV），则签名可能是可检测的。GWB诱导极化的特征预计将小于CMB的~300 nK的均方根幅度;比最近才解决的温度各向异性的幅度低两个数量级以上。检测将只需要适度的角分辨率（~ 1 °），但是需要在有限的（~3%）和连续的天空上进行长时间的积分（~1年）。六个月的夜晚，极端干燥和稳定的天气，以及天顶周围天空的精确旋转，使南极站成为这个雄心勃勃的项目的理想地面站点。目前正在建造一个能够探测全球暖带特征的独特的CMB偏振计，将于2003年部署到南极。正在建造BICEP的团队包括四名高级实验人员，他们成功地将复杂的测热仪器部署到南极。BICEP将在100和150 GHz同时运行，以最大限度地减少和识别来自极化天体物理前景的混淆。在这些频率下，适度的（因此相对容易部署和维护）20厘米主孔径将提供1度的分辨率。在100 GHz和0.7 deg.在150 GHz。通过结合一种新的偏振敏感测辐射热探测器技术开发的普朗克（2007年发射）通过四个独立的信号差分水平和精心优化的观测策略，BICEP将在积分的第一个小时内达到当前CMB偏振的极限，在第一周内达到普朗克超过天空1%的灵敏度，并在1 °的临界角尺度上精确测量CMB偏振。到10 °BICEP将服务于更广泛的宇宙学家和天体物理学家社区，（i）在这个令人兴奋的新领域开创一个数量级的改进，（ii）表征最终将限制这种类型测量的弥漫天体物理前景（这是直接感兴趣的银河天文学家），（iii）展示新的技术和方法，承诺将广泛的重要性，毫米波偏振，以及（iv）在这方面有良好记录的实验室为研究生和博士后研究员提供出色的培训。观测宇宙学目前正在经历一场复兴，它吸引了公众的想象力，并成为激发人们对科学兴趣的最有效工具之一。在CMB中检测到GWB的签名将代表基础物理学和宇宙学的胜利，这将彻底改变我们对宇宙起源的理解。

The Cosmic Microwave Background (CMB) provides three strong but circumstantial pieces of evidence that the visible Universe was created by the superluminal inflation of a tiny volume of space: the near isotropy of the horizon, the flatness of space, and the phase-synchronicity of acoustic oscillations in the early universe. The goal of better understanding the origins of the Universe requires probing this epoch of Inflation directly. The most promising probe of Inflation is the unique signature that the GWB imprints on the polarization of the CMB. The amplitude of this signature depends on the energy-scale of Inflation. If the energy scale is typical of Grand Unification Theory (GUT) (10^15 3 x 10^16 GeV), the signature may be detectable. The signature of the GWB-induced polarization is expected to be less than an rms amplitude of ~300 nK of the CMB; more than two orders of magnitude below the amplitude of the temperature anisotropies that have only recently been resolved. Detection will require only modest angular resolution (~ 1 deg.), but will require long integration (~1 year) on a restricted (~3%) and contiguous patch of sky. The six-month night, the extremely dry and stable weather, and the precise rotation of the sky about the zenith make South Pole Station the ideal terrestrial site for this ambitious project. A CMB polarimeter (BICEP) uniquely capable of detecting the signature of the GWB is now under construction and will be available for deployment to the South Pole in 2003. The team that is building BICEP includes four senior experimentalists who have successfully fielded sophisticated bolometric instrumentation to the Antarctic. BICEP will operate simultaneously at 100 and 150 GHz in order to both minimize and recognize confusion from polarized astrophysical foregrounds. At these frequencies, a modest (and thus relatively easy to deploy and maintain) 20-cm primary aperture will provide a resolution of 1deg. at 100 GHz and 0.7 deg. at 150 GHz. By combining a new polarization-sensitive bolometric detector technology developed for Planck (2007 launch) with four independent levels of signal differencing and a carefully optimized observing strategy, BICEP will reach the current limit on CMB polarization in the first hour of integration, reach the sensitivity of Planck over 1% of the sky in the first week, and precisely measure CMB polarization on the critical angular scales of 1 deg. to 10 deg. BICEP will serve the broader community of cosmologists and astrophysicists by (i) pioneering an orders-of-magnitude improvement in this exciting new field, (ii) characterizing the diffuse astrophysical foregrounds that will ultimately limit measurements of this type (and which are of direct interest to Galactic astronomers), (iii) demonstrating new technologies and methodologies that promise to be of broad importance to millimeter-wave polarimetry, and (iv) providing excellent training for graduate students and postdoctoral fellows in labs which have a very strong track-record in this regard. Observational cosmology is currently enjoying a renaissance that has captured the public imagination, and serves as one of the most effective vehicles for stimulating interest in science in general. Detection of the signature of the GWB in the CMB would represent a triumph of fundamental physics and cosmology that would revolutionize our understanding of the origins of the Universe.