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A comprehensive study of modulation effects on CMB polarization
General Relativity and Gravitation ( IF 2.8 ) Pub Date : 2022-04-17 , DOI: 10.1007/s10714-022-02921-8
Rahul Kothari

The Cosmic Microwave Background is characterized by temperature and linear polarization fields. Dipole modulation in the temperature field has been extensively studied in the context of hemispherical power asymmetry. In this article, we show that a dipole modulation, and in general, any kind of modulation isn’t allowed in the E and B modes. This is the main result of this paper. This result explains why no evidence of modulation in E mode has been found in the literature. On the contrary, the linear polarization fields Q and U have no such restrictions. We show that modulation under certain situations can be thought of as local U(1) gauge transformations on the surface of a sphere. As far as the modulation function is concerned, we show that physical considerations enforce it to be (i) a spin 0 field and (ii) a scalar under parity. As masking is a specific type of modulation, our study suggests that a direct masking of E mode isn’t also possible. Masking in E map can only be applied through Q and U fields. This means that in principle, leaking of E and B mode powers into each other is unavoidable.



中文翻译:

CMB极化调制效应综合研究

宇宙微波背景的特点是温度和线性偏振场。在半球功率不对称的背景下,已经广泛研究了温度场中的偶极调制。在本文中,我们展示了偶极调制,一般来说,在EB模式中不允许使用任何类型的调制。这是本文的主要成果。这个结果解释了为什么在文献中没有发现E模式调制的证据。相反,线性偏振场QU没有这样的限制。我们表明,在某些情况下调制可以被认为是局部U(1) 球面上的规范变换。就调制函数而言,我们表明物理考虑强制它是(i)自旋0场和(ii)奇偶校验下的标量。由于掩蔽是一种特定类型的调制,我们的研究表明直接掩蔽E模式也是不可能的。E映射中的掩蔽只能通过QU字段应用。这意味着原则上,EB模式功率相互泄漏是不可避免的。

更新日期:2022-04-18
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