Collaborative Research: Imaging the Beginning of Time from the South Pole: Completing the BICEP Array Survey

“大爆炸”理论为我们的宇宙从最早的已知时期到随后的大规模演化的起源提供了一个既定的宇宙学模型。然而，这个理论留下了解释初始条件的问题。目前的想法是一致的，整个可观测宇宙是在一个戏剧性的，指数“膨胀”的亚核体积中产生的，持续了大约一万亿分之一的一万亿分之一秒。在这个短暂的暴胀期之后，宇宙继续膨胀，但速度变慢了。虽然这种基本的“暴胀范式”被大多数宇宙学家所接受，但导致暴胀的详细物理机制仍不为人所知，但有一个可验证的预测，即这种剧烈的时空膨胀会产生原始引力波，现在正在膨胀的宇宙中传播，并形成宇宙引力波背景（CGB）。CGB振幅定义了暴胀的能量尺度，它在宇宙微波背景（CMB）辐射的极化中留下了一个微弱的特征。因此，探测这种偏振特征可以说是当今宇宙学中最重要的目标。这个奖项将继续解决人类提出的最古老的问题“宇宙是如何开始的？”，它是通过在地球上最恶劣的地方之一——南极洲的阿蒙森-斯科特南极站进行的观察来实现的。最近，由社区推动的Astro2020年十年调查报告《2020年代天文学和天体物理学的发现之路》重申了寻找原始引力波和暴胀的b模偏振特征的重要性，并特别支持在南极洲和智利进行系统支持的CMB实验，以开展CMB第4阶段的科学研究。最近发布的BICEP结果对暴胀模型提出了严格的限制，这是第一次远远超出了仅用温度数据可以完成的范围，并且排除了两种以前流行的单场模型——自然暴胀和简单的单项势。该合同旨在完成所有四个BICEP阵列接收器的部署，然后将其作为第三阶段+一代观测系统进行操作。BICEP阵列将测量六个频段的偏振天空，在保守地考虑了银河系尘埃、银河系同步加速器和CMB透镜前景后，根据已取得的性能外推，对PGW振幅的最终灵敏度达到σ(r) > 0.003。这些测量结果将是对慢滚膨胀模型的最终检验，该模型通常预测引力波信号在大约r=0.01以上。因此，BICEP阵列将实现NASA/DOE/NSF CMB研究工作组在2005年设定的目标，即达到这一级别的灵敏度，并被Astro2010确认为“最令人兴奋的探索”，并推进Astro2020年十年调查强烈支持的b模式搜索。该项目将继续为本科生、研究生和博士后提供优秀的培训，包括那些在这方面有杰出记录的实验室中代表性不足的群体。宇宙学和南极洲的研究都吸引了公众的想象力，使这一组合成为激发科学兴趣的非常有效的工具。这个项目推进了NSF宇宙大构想窗口的目标。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The theory of the "Big Bang" provides an established cosmological model for the origin of our Universe from its earliest known periods through its subsequent large-scale evolution. However, this theory leaves open the question of explaining the initial conditions. Current thoughts are consistent with the entire observable Universe being spawned in a dramatic, exponential "Inflation" of a sub-nuclear volume that lasted about one trillionth of a trillionth of a trillionth of a second. Following this short inflationary period, the Universe continues to expand, but at a less rapid rate. While this basic "Inflationary paradigm" is accepted by most cosmologists, the detailed physics mechanism responsible for inflation is still not known, but there is a testable prediction that this violent space-time expansion would have produced primordial gravitational waves now propagating through the expanding Universe and forming a cosmic gravitational-wave background (CGB). The CGB amplitude defines the energy scale of Inflation that imprints a faint signature in the polarization of the Cosmic Microwave Background (CMB) radiation. Therefore, detecting this polarization signature is arguably the most important goal in cosmology today. This award will continue addressing the oldest question ever posed by mankind "How did the Universe begin?", and it does so via observations made at one of the harshest places on Earth – the Amundsen-Scott South Pole Station in Antarctica. The most recent, community driven Decadal Survey Astro2020 report “Pathways to Discovery in Astronomy and Astrophysics for the 2020s” reaffirmed the importance of search for B-modes polarization signatures of primordial gravitational waves and Inflation, and specifically endorsed the CMB Stage-4 science to be pursued by systematically supported CMB experiments in Antarctica and Chile. The recently released BICEP results place stringent limits on Inflationary models which, for the first time, go well beyond what can be done with temperature data alone, and which rule out two entire classes of previously popular single-field models—natural Inflation and simple monomial potentials. This award aims to complete deployment of all four BICEP Array receivers and then operate them as the Stage-3+ generation observing system. BICEP Array will measure the polarized sky in six frequency bands to reach an ultimate sensitivity to the amplitude of PGW of σ(r) ≲ 0.003, extrapolating from achieved performance, and after conservatively accounting for the Galactic dust, Galactic synchrotron and CMB lensing foregrounds. These measurements will be a definitive test of slow-roll models of Inflation, which generally predict a gravitational-wave signal above approximately r=0.01. BICEP Array will therefore realize the goal set by the NASA/DOE/NSF Task Force for CMB Research in 2005 to achieve sensitivity at this level, and confirmed as “the most exciting quest of all” by the Astro2010, and advance the B-mode search strongly endorsed by the Astro2020 Decadal Survey. The project will continue to provide excellent training for undergraduate and graduate students and postdoctoral fellows including those from underrepresented groups in laboratories that have exceptional track records in this regard. Cosmology and research in Antarctica both capture the public imagination, making this combination a remarkably effective vehicle for stimulating interest in science. This project advances the goals of the NSF Windows on the Universe Big Idea.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.