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

宇宙微波背景（CMB）提供了三个强有力但间接的证据，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向性。为了更好地理解宇宙的起源，我们需要直接探索这个暴胀时代。对暴胀最有希望的探测是GWB在宇宙微波背景的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。如果能量尺度是典型的大统一理论（GUT） （10^15 3 x 10^16 GeV），则可以检测到该特征。gwb诱导极化的特征预计小于CMB的rms振幅~300 nK；比最近才解决的温度各向异性的振幅低两个数量级以上。探测只需要适度的角分辨率（~1度），但需要在有限的（~3%）和连续的天空斑块上进行长时间的集成（~1年）。六个月的夜晚，极其干燥和稳定的天气，以及天顶周围精确的天空旋转，使南极站成为这个雄心勃勃的项目的理想地点。一个CMB偏振计（BICEP）唯一能够探测GWB的信号，目前正在建造中，并将于2003年部署到南极。建造BICEP的团队包括四名高级实验学家，他们已经成功地在南极部署了精密的辐射测量仪器。BICEP将在100 GHz和150 GHz同时工作，以最大限度地减少和识别来自偏振天体物理前景的混淆。在这些频率下，一个适度的（因此相对容易部署和维护）20厘米的主孔径将提供1度的分辨率。在100 GHz和0.7度，在150 GHz。通过结合为普朗克（2007年发射）开发的具有四个独立信号差分水平的新型偏振敏感辐射热测量探测器技术和精心优化的观测策略，BICEP将在集成的第一个小时内达到目前对CMB偏振的限制，在第一周内达到普朗克对1%天空的灵敏度。BICEP将通过以下方式服务于更广泛的宇宙学家和天体物理学家社区：(1)在这一令人兴奋的新领域开创了一个数量级的改进；(2)描述弥漫性天体物理学前景，最终将限制这类测量（这与银河系天文学家直接相关）。（三）展示有望对毫米波偏振学具有广泛重要性的新技术和方法；（四）在实验室为研究生和博士后提供优秀的培训，这些实验室在这方面有很强的跟踪记录。观测宇宙学目前正在复兴，它抓住了公众的想象力，并成为激发人们对科学兴趣的最有效的工具之一。在CMB中探测到GWB的特征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.