宇宙微波背景去透镜效应的再研究：残余偏差和简单修正
Cosmic Microwave Background Delensing Revisited: Residual Biases and a Simple Fix
摘要：
去透镜过程是一个有效的工具，用于消除在宇宙微波背景中透镜诱导的$B$模式偏振，以允许深入搜索原始的$B$模式。然而，如果目标$B$模式信号与多极$l$空间中的透镜$B$模式（$\sim 300<l<2000$）显著重叠，则存在于文献中的去透镜算法失效.在本文中，我们确定故障的原因是输入$B$ -地图和偏转场估计（$EB$）之间的相关性。这种偏见的幅度是量化的数值模拟和解析推导的函数形式相比。我们还提出了一个修改后的脱镜片程序，以规避偏见。虽然新识别的偏差不影响搜索度标度$B$ -模式产生的张量扰动，修改后的去透镜算法使得有可能执行深搜索的高$l$ $B$ -模式，如那些产生的补丁再电离，宇宙弦，或旋转的偏振角。最后，我们估计如何以及未来的偏振实验可以做在检测张量和宇宙弦产生的$B$模式后，去透镜和评论不同的调查策略。
英文摘要：
The delensing procedure is an effective tool for removing lensing-induced $B$-mode polarization in the Cosmic Microwave Background to allow for deep searches of primordial $B$-modes. However, the delensing algorithm existing in the literature breaks down if the target $B$-mode signals overlap significantly with the lensing $B$-mode ($\sim 300<l<2000$) in multipole-$l$ space. In this paper, we identify the cause of the breakdown to be correlations between the input $B$-map and the deflection field estimator ($EB$). The amplitude of this bias is quantified by numerical simulations and compared to the analytically derived functional form. We also propose a revised delensing procedure that circumvents the bias. While the newly identified bias does not affect the search of degree scale $B$-mode generated by tensor perturbations, the modified delensing algorithm makes it possible to perform deep searches of high-$l$ $B$-modes such as those generated by patchy reionization, cosmic strings, or rotation of polarization angles. Finally, we estimate how well future polarization experiments can do in detecting tensor- and cosmic string- generated $B$-mode after delensing and comment on different survey strategies.
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