[论文解读] Planck 2018 results. IX. Constraints on primordial non-Gaussianity

Planck Collaboration, Y. Akrami+158 more|arXiv (Cornell University)|May 14, 2019

Cosmology and Gravitation Theories参考文献 208被引用 153

一句话总结

Planck 分析完整任务的 CMB 温度和 E 模极化，以约束原始非高斯性，得到对 local、equilateral 和 orthogonal f_NL 的严格限制，并探索广泛的 NG 形状。

ABSTRACT

We analyse the Planck full-mission cosmic microwave background (CMB) temperature and E-mode polarization maps to obtain constraints on primordial non-Gaussianity (NG). We compare estimates obtained from separable template-fitting, binned, and modal bispectrum estimators, finding consistent values for the local, equilateral, and orthogonal bispectrum amplitudes. Our combined temperature and polarization analysis produces the following results: f_NL^local = -0.9 +\- 5.1; f_NL^equil = -26 +\- 47; and f_NL^ortho = - 38 +\- 24 (68%CL, statistical). These results include the low-multipole (4 <= l < 40) polarization data, not included in our previous analysis, pass an extensive battery of tests, and are stable with respect to our 2015 measurements. Polarization bispectra display a significant improvement in robustness; they can now be used independently to set NG constraints. We consider a large number of additional cases, e.g. scale-dependent feature and resonance bispectra, isocurvature primordial NG, and parity-breaking models, where we also place tight constraints but do not detect any signal. The non-primordial lensing bispectrum is detected with an improved significance compared to 2015, excluding the null hypothesis at 3.5 sigma. We present model-independent reconstructions and analyses of the CMB bispectrum. Our final constraint on the local trispectrum shape is g_NLl^local = (-5.8 +\-6.5) x 10^4 (68%CL, statistical), while constraints for other trispectra are also determined. We constrain the parameter space of different early-Universe scenarios, including general single-field models of inflation, multi-field and axion field parity-breaking models. Our results provide a high-precision test for structure-formation scenarios, in complete agreement with the basic picture of the LambdaCDM cosmology regarding the statistics of the initial conditions (abridged).

研究动机与目标

• 将原始非高斯性作为对膨胀模型的探针进行动机阐述与定量分析。
• 结合 Planck 温度和低倍极化数据以约束 NG 形状。
• 测试包括 local、equilateral、orthogonal 以及尺度相关模型在内的广泛 NG 模板。
• 通过对前沿源和仪器系统误差的广泛验证来评估鲁棒性。

提出的方法

• 使用可分离模板拟合、分箱和最优模态三阶谱估计量来测量 CMB 的三阶谱。
• 纳入低阶极化数据 (4 ≤ ℓ < 40) 以改善约束。
• 评估对三阶谱的非原始贡献，如引力透镜效应与星系外点源。
• 提供对 CMB 三阶谱的模型无关重建。
• 扩展分析到四阶谱以约束 g_NL_local 及其他四阶谱形状。

实验结果

研究问题

• RQ1 使用 Planck 数据时，local、equilateral 和 orthogonal 形状的原始 NG 振幅是多少？
• RQ2 极化数据是否提升 NG 约束及结果的鲁棒性？
• RQ3 包括 running、等价、等变性、isocurvature、共振和奇偶性违规等广泛模型的 NG 状态如何？
• RQ4 非原始贡献（透镜效应、点源）如何影响 NG 估计？
• RQ5 Planck 对 NG 的约束对早期宇宙膨胀模型有何含义？

主要发现

• 温度与极化联合分析给出 f_NL^local = -0.9 ± 5.1 (68% CL)。
• f_NL^equil = -26 ± 47 (68% CL)。
• f_NL^ortho = -38 ± 24 (68% CL)。
• g_NL^local = (-5.8 ± 6.5) × 10^4 (68% CL)。
• 仅极化的三阶谱提供稳健的约束，其灵敏度可与温度数据结果媲美，并且与先前的测量一致。
• Lensing 三阶谱在 3.5σ 显著性水平被检测到，拒绝零假设；未发现超出标准形状的其他 NG 形状的令人信服信号。