We investigate the prior dependence on the inferred spectrum of primordial tensor perturbations, in light of recent results from BICEP2 and taking into account a possible dust contribution to polarized anisotropies. We highlight an optimized parameterization of the tensor power spectrum, and adoption of a logarithmic prior on its amplitude $A_T$, leading to results that transform more evenly under change of pivot scale. In the absence of foregrounds the tension between the results of BICEP2 and Planck drives the tensor spectral index $n_T$ to be blue-tilted in a joint analysis, which would be in contradiction to the standard inflation prediction ($n_T<0$). When foregrounds are accounted for, the BICEP2 results no longer require non-standard inflationary parameter regions. We present limits on primordial $A_T$ and $n_T$, adopting foreground scenarios put forward by Mortonson & Seljak and motivated by Planck 353 GHz observations, and assess what dust contribution leaves a detectable cosmological signal. We find that if there is sufficient dust for the signal to be compatible with standard inflation, then the primordial signal is too weak to be robustly detected by BICEP2 if Planck+WMAP upper limits from temperature and E-mode polarization are correct.
Contribution to the 2022 Cosmology session of the 56th Rencontres de Moriond: Moment expansion of polarized dust SED: A new path towards capturing the CMB $B$-modes with LiteBIRD
The Simons Observatory: Assessing the Impact of Dust Complexity on the Recovery of Primordial $B$-modes
Princeton University（普林斯顿大学）；Stanford University（斯坦福大学）；California Institute of Technology（加州理工学院）；The International School for Advanced Studies (SISSA)（高级研究国际学校）；University of Oxford（牛津大学）；The National Institute for Nuclear Physics (INFN)（意大利国家核物理研究所）；The Institute for Fundamental Physics of the Universe (IFPU)（宇宙基础物理研究所）；The University of Manchester（曼彻斯特大学）；University of Virginia（弗吉尼亚大学）；The National Institute for Nuclear Physics (INFN) - Sezione di Catania（意大利国家核物理研究所卡塔尼亚分部）
Impact on the tensor-to-scalar ratio of incorrect Galactic foreground modelling
许多宇宙微波背景实验的一个关键目标是通过大尺度的B模偏振信号来探测引力波。要提取这样的信号，需要对银河系的污染进行建模。使用普朗克实验作为一个例子，我们调查的影响不正确的建模前景的估计偏振CMB，量化的偏置张量标量比r，和光学深度τ。我们使用贝叶斯参数估计方法从30-353 GHz的模拟观测中估计CMB，同步加速器和热尘埃成分，从拟合模拟数据的模型开始，对于r=0的模型，在95%置信度下返回r<0.03，对于r=0.1的模型，返回r=0.09+-0.03。然后，我们引入一组模拟数据和假设模型之间的不匹配。包括同步加速器光谱指数随频率的曲率，但假设幂律模型，可以使r偏高~1-sigma（delta r ~ 0.03）。一个类似的偏见是看到一个修改后的黑体频率依赖性的热尘埃，不正确地建模为幂律。如果在模型中允许太多的自由度，例如用物理上合理的先验拟合天空中3度像素的光谱指数，我们发现通过有效地将指数设置为错误的值，r可以被偏置到~3-sigma高。通过减少参数或添加额外的前景数据来增加信噪比可减少偏差。我们还发现，忽略1%的偏振自由或旋转尘埃成分对r的影响可以忽略不计。这些测试突出了以允许足够复杂的方式对前景进行建模的重要性，同时最大限度地减少自由参数的数量。
