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A minimal power-spectrum-based moment expansion for CMB B-mode searches
Journal of Cosmology and Astroparticle Physics ( IF 6.4 ) Pub Date : 2021-05-18 , DOI: 10.1088/1475-7516/2021/05/047
S. Azzoni 1, 2 , M.H. Abitbol 1 , D. Alonso 1 , A. Gough 1, 3 , N. Katayama 2 , T. Matsumura 2
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The characterization and modeling of polarized foregrounds has become a critical issue in the quest for primordial B-modes. A typical method to proceed is to factorize and parametrize the spectral properties of foregrounds and their scale dependence (i.e. assuming that foreground spectra are well described everywhere by their sky average). Since in reality foreground properties vary across the Galaxy, this assumption leads to inaccuracies in the model that manifest themselves as biases in the final cosmological parameters (in this case the tensor-to-scalar ratio r). This is particularly relevant for surveys over large fractions of the sky, such as the Simons Observatory (SO), where the spectra should be modeled over a distribution of parameter values. Here we propose a method based on the existing “moment expansion” approach to address this issue in a power-spectrum-based analysis that is directly applicable in ground-based multi-frequency data. Additionally, the method uses only a small set of parameters with simple physical interpretation, minimizing the impact of foreground uncertainties on the final B-mode constraints. We validate the method using SO-like simulated observations, recovering an unbiased estimate of the tensor-to-scalar ratio r with standard deviation σ(r) ≃ 0.003, compatible with official forecasts. When applying the method to the public BICEP2/Keck data, we find an upper bound r < 0.06 (95% C.L.), compatible with the result found by BICEP2/Keck when parametrizing spectral index variations through a scale-independent frequency decorrelation parameter. We also discuss the formal similarities between the power spectrum-based moment expansion and methods used in the analysis of CMB lensing.



中文翻译:

用于 CMB B 模式搜索的基于最小功率谱的矩扩展

极化前景的表征和建模已成为寻求原始B模式的关键问题。一种典型的方法是对前景的光谱特性及其尺度依赖性进行分解和参数化(即假设前景光谱在任何地方都可以通过天空平均值得到很好的描述)。由于实际上整个银河系的前景属性各不相同,因此该假设导致模型不准确,表现为最终宇宙学参数的偏差(在这种情况下,张量与标量之比r)。这对于大部分天空的调查尤其相关,例如西蒙斯天文台 (SO),其中的光谱应根据参数值的分布进行建模。在这里,我们提出了一种基于现有“矩扩展”方法的方法,以在基于功率谱的分析中解决这个问题,该分析直接适用于地面多频数据。此外,该方法仅使用具有简单物理解释的一小组参数,最大限度地减少前景不确定性对最终B模式约束的影响。我们使用类似 SO 的模拟观测来验证该方法,恢复张量与标量比r的无偏估计,标准偏差为 σ( r) ≃ 0.003,与官方预测一致。当将该方法应用于公共 BICEP2/ Keck数据时,我们发现上限r < 0.06 (95% CL),与 BICEP2/ Keck在通过与尺度无关的频率去相关参数参数化频谱指数变化时发现的结果兼容。我们还讨论了基于功率谱的矩扩展与 CMB 透镜分析中使用的方法之间的形式上的相似性。

更新日期:2021-05-18
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