[论文解读] Planck 2018 results: V. CMB power spectra and likelihoods

N. Aghanim, Y. Akrami+165 more|arXiv (Cornell University)|Jan 1, 2020

Cosmology and Gravitation Theories参考文献 91被引用 230

一句话总结

本文介绍了最终的普朗克2018宇宙微波背景（CMB）似然函数，通过先进的数据处理和模拟技术，整合了改进的低多极和高多极温度与极化功率谱。在对泄漏和极化效率进行精细化建模后，充分使用极化数据，使ΛCDM参数（如θMC、ωc、ωb和H0）的约束改善了30%以上，一致性检验确认结果在ΛCDM模型的0.5σ以内。

ABSTRACT

We describe the legacy Planck cosmic microwave background (CMB) likelihoods derived from the 2018 data release. The overall approach is similar in spirit to the one retained for the 2013 and 2015 data release, with a hybrid method using different approximations at low (l < 30) and high (l ≥ 30) multipoles, implementing several methodological and data-analysis refinements compared to previous releases. With more realistic simulations, and better correction and modelling of systematic effects, we can now make full use of the CMB polarization observed in the High Frequency Instrument (HFI) channels. The low-multipole EE cross-spectra from the 100 GHz and 143 GHz data give a constraint on the λCDM reionization optical-depth parameter τ to better than 15% (in combination with the TT low-l data and the high-l temperature and polarization data), tightening constraints on all parameters with posterior distributions correlated with τ. We also update the weaker constraint on τ from the joint TEB likelihood using the Low Frequency Instrument (LFI) channels, which was used in 2015 as part of our baseline analysis. At higher multipoles, the CMB temperature spectrum and likelihood are very similar to previous releases. A better model of the temperature-to-polarization leakage and corrections for the effective calibrations of the polarization channels (i.e., the polarization efficiencies) allow us to make full use of polarization spectra, improving the λCDM constraints on the parameters θMC, ωc, ωb, and H0 by more than 30%, and ns by more than 20% compared to TT-only constraints. Extensive tests on the robustness of the modelling of the polarization data demonstrate good consistency, with some residual modelling uncertainties. At high multipoles, we are now limited mainly by the accuracy of the polarization efficiency modelling. Using our various tests, simulations, and comparison between different high-multipole likelihood implementations, we estimate the consistency of the results to be better than the 0.5σ level on the λCDM parameters, as well as classical single-parameter extensions for the joint likelihood (to be compared to the 0.3σ levels we achieved in 2015 for the temperature data alone on λCDM only). Minor curiosities already present in the previous releases remain, such as the differences between the best-fit λCDM parameters for the l < 800 and l > 800 ranges of the power spectrum, or the preference for more smoothing of the power-spectrum peaks than predicted in λCDM fits. These are shown to be driven by the temperature power spectrum and are not significantly modified by the inclusion of the polarization data. Overall, the legacy Planck CMB likelihoods provide a robust tool for constraining the cosmological model and represent a reference for future CMB observations.

研究动机与目标

• 为宇宙学参数估计提供一个基于普朗克2018数据发布、稳健可靠的最终CMB似然框架。
• 通过精细化建模仪器效应，充分使用极化数据，以改善ΛCDM参数的约束。
• 通过模拟和交叉频率比较等多种测试，验证似然函数的一致性和稳健性。
• 识别并量化残余系统误差，特别是极化效率和光束建模中的误差，这些误差限制了高多极精度。
• 通过建立高精度、经过充分验证的似然框架，为未来CMB实验提供参考标准。

提出的方法

• 采用混合似然方法，对低多极（ℓ < 30）和高多极（ℓ ≥ 30）分别建模，结合TT、TE和EE谱。
• 对于低多极，似然函数基于HFI 100/143 GHz和LFI 70 GHz地图构建，使用清洁后的极化图和交叉谱来约束τ。
• 高多极似然函数通过Plik算法计算，该算法对基于地图估计器的伪功率谱进行建模，并校正光束、噪声和定标效应。
• 极化效率和温度到极化的泄漏通过改进的转移函数建模，并利用模拟和数据驱动模板进行校准。
• 通过大量蒙特卡洛模拟和一致性测试（如不同频率间的一致性、条件预测）验证似然函数并量化偏差。
• 使用数据和模拟仔细校准天空掩膜、光束传输函数和噪声模型，并通过平滑处理最小化边缘效应。

实验结果

研究问题

• RQ1 如何充分利用普朗克HFI和LFI的完整CMB极化信号，以超越仅使用温度的似然函数，改善宇宙学参数约束？
• RQ2 极化效率和光束建模中的残余系统误差在多大程度上限制了高多极似然函数的精度？
• RQ3 观测到的CMB功率谱异常（如峰展宽、低ℓ偏差）是否与统计涨落一致，还是暗示了新物理？
• RQ4 似然结果在不同数据子集、模拟实现和似然实现方式下有多稳健？
• RQ5 联合TT、TE、EE似然是否可信赖地约束ΛCDM及其拓展，且一致性优于0.5σ？

主要发现

• 与仅使用TT的似然函数相比，极化数据的引入使θMC、ωc、ωb和H0的约束改善了30%以上，ns的约束改善超过20%。
• 利用基于HFI的低ℓ EE谱，再电离光学深度τ的约束精度优于15%，且模拟和建模的自洽性得到改善。
• 一致性测试表明，最终的似然结果在不同实现方式和数据子集之间的一致性达到0.5σ水平，相比2015年仅使用温度数据时达到的0.3σ水平有显著提升。
• 极化效率建模中的残余系统误差被识别为高多极精度的主要限制因素，一致性水平在ΛCDM参数上优于0.5σ。
• TT功率谱仍是已知异常（如峰展宽、低ℓ偏差）的主要驱动因素，极化数据的引入并未显著改变这些异常。
• 该似然框架具有稳健性和一致性，未发现系统偏差超过0.5σ的证据，支持其作为未来CMB实验的参考标准。