[论文解读] Cosmic birefringence tomography and calibration-independence with reionization signals in the CMB

Blake D. Sherwin, Toshiya Namikawa|arXiv (Cornell University)|Aug 20, 2021

Cosmology and Gravitation Theories被引用 9

一句话总结

本文提出了一种新型的校准无关方法，通过对比再电离时期（z ~ 8）与复合时期（z ~ 1100）宇宙微波背景（CMB）信号的偏振旋转角度，测量宇宙双折射。该方法利用轴子样粒子等宇称破坏性物理的红移依赖响应，消除仪器角度校准误差，实现对双折射红移起源的层析约束，预测未来任务（如LiteBIRD）可实现约0.05°的灵敏度。

ABSTRACT

The search for cosmic polarization rotation or birefringence in the CMB is well-motivated because it can provide powerful constraints on parity-violating new physics, such as axion-like particles. In this paper we point out that since the CMB polarization is produced at two very different redshifts - it is generated at both reionization and recombination - new parity-violating physics can generically rotate the polarization signals from these different sources by different amounts. We explore two implications of this. First, measurements of CMB birefringence are challenging because the effect is degenerate with a miscalibration of CMB polarization angles; however, by taking the difference of the reionization and recombination birefringence angles (measured from different CMB angular scales), we can obtain a cosmological signal that is immune to instrumental angle miscalibration. Second, we note that the combination with other methods for probing birefringence can give tomographic information, constraining the redshift origin of any physics producing birefringence. We forecast that the difference of the reionization and recombination birefringence angles can be competitively determined to within ~0.05 degrees for future CMB satellites such as LiteBIRD. Although much further work is needed, we argue that foreground mitigation for this measurement should be less challenging than for inflationary B-mode searches on similar scales due to larger signals and lower foregrounds.

研究动机与目标

• 解决CMB偏振测量中宇宙双折射与仪器角度校准误差之间的退化问题。
• 开发一种方法，通过利用CMB偏振在不同红移源的特性，将宇宙双折射信号与校准误差分离，实现独立于校准误差的测量。
• 通过比较再电离与复合时期的双折射，提供关于宇称破坏性物理红移演化特性的层析信息。
• 预测未来CMB实验（如LiteBIRD）对再电离与复合时期双折射角度差异的灵敏度。
• 评估该方法对前景污染和残余系统误差的鲁棒性。

提出的方法

• 该方法利用再电离与复合时期在不同红移产生CMB偏振的特性，若其背后的物理机制（如轴子样粒子）随时间演化，则可能产生不同的双折射角度。
• 通过低多极和高多极的EB交叉功率谱，分别测量再电离与复合时期的双折射角度差值Δβ = β_reio − β_recomb。
• 仪器角度误差在差值中被抵消，使测量结果与校准无关，前提是两种成分均使用相同的频率清洗权重。
• 该方法基于类似LiteBIRD的噪声模型进行预测，结合分量分离产生的残余前景功率（如Errard等，2016年）以评估实际灵敏度。
• 假设前景对EB谱的影响小于对BB谱的影响，表明前景抑制可能比标准B模搜索更简单。
• 该方法依赖于一个假设：对低ℓ和高ℓ偏振分析均采用相同的频率清洗策略，以保持误差抵消。

Figure 1: Constraints on the birefringence angle difference as a function of CMB polarization noise level, with different delensing efficiencies assumed (we also assume $f_{\mathrm{sky}}=0.7$ .) Solid lines of different colours assume different constant delensing efficiencies; the dotted line labell

实验结果

研究问题

• RQ1 再电离与复合时期CMB信号的双折射角度差异是否可用于实现校准无关的测量？
• RQ2 轴子样粒子等宇称破坏场的红移依赖响应是否会导致偏振旋转角度的可测量差异？
• RQ3 前景残余对Δβ测量灵敏度的退化程度如何？其灵敏度是否仍具竞争力？
• RQ4 该方法能否提供关于导致双折射的新物理红移起源的层析信息？
• RQ5 Δβ测量的校准无关性对如频率依赖仪器误差等系统效应的鲁棒性如何？

主要发现

• 由于在减去再电离与复合测量时共同模式误差被抵消，双折射角度差值Δβ对仪器角度校准误差不敏感。
• 该方法可通过比较z ~ 8与z ~ 1100处的双折射，实现对宇称破坏性物理（如轴子样粒子）红移演化的层析约束。
• 对于未来CMB实验（如LiteBIRD），该方法预测对角度差值的灵敏度可达σ(Δβ) ≈ 0.05度。
• 即使包含来自分量分离的现实前景残余，约束性能仅轻微退化至σ(Δβ) ≈ 0.09度，仍具竞争力。
• 由于相关尺度上本征信号更强且前景污染更低，Δβ测量的信噪比预计高于标准B模搜索。
• 在对低ℓ和高ℓ偏振分析均采用相同频率清洗权重的假设下，该方法具有鲁棒性，可保持误差抵消。

Figure 2: Variation of the constraints in Figure 1 with the minimum multipole used in the analysis and with the presence of foreground residuals. Solid lines assume lensing B-power has been reduced by a factor 0.3, dotted lines assume no delensing (and both neglect foreground residuals). Purple colo