The cosmic microwave background (CMB) lensing power spectrum is a powerful probe of the late-time Universe, encoding valuable information about cosmological parameters such as the sum of neutrino masses and dark energy equation of state. However, the presence of anisotropic cosmic birefringence can bias the reconstructed CMB lensing power spectrum using CMB polarization maps, particularly at small scales, and affect the constraints on these parameters. Upcoming experiments, which will be dominated by the polarization lensing signal, are especially susceptible to this bias. We identify the dominant contribution to this bias as an 𝑁(1)𝐿-like noise, caused by anisotropic rotation instead of lensing. We show that, for an CMB-S4-like experiment, a scale-invariant anisotropic rotation field with a standard deviation of 0.05 degrees can suppress the small-scale lensing power spectrum (𝐿≳2000) at a comparable level to the effect of massive neutrino with ∑𝑖𝑚𝜈𝑖=50  meV, making rotation field an important source of degeneracy in neutrino mass measurement for future CMB experiments. We provide an analytic expression and a simulation-based estimator for this 𝑁(1)𝐿-like noise, which allows for efficient forecasting and mitigation of the bias in future experiments. Furthermore, we investigate the impact of a non-scale-invariant rotation power spectrum on the reconstructed lensing power spectrum and find that an excess of power in the small-scale rotation power spectrum leads to a larger bias. Our work provides an effective numeric framework to accurately model and account for the bias caused by anisotropic rotation in future CMB lensing measurements.

中文翻译：

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对重建的 CMB 透镜功率谱的旋转诱导偏置的有效估计


宇宙微波背景 （CMB） 透镜功率谱是晚期宇宙的强大探测器，编码有关宇宙学参数的宝贵信息，例如中微子质量之和和暗能量状态方程。然而，各向异性宇宙双折射的存在会使使用 CMB 偏振图重建的 CMB 透镜功率谱产生偏差，特别是在小尺度上，并影响对这些参数的约束。即将进行的实验将以偏振透镜信号为主，特别容易受到这种偏差的影响。我们将这种偏差的主要贡献确定为由各向异性旋转而不是透镜引起的类似 N（1）L 的噪声。结果表明，对于类 CMB-S4 实验，标准差为 0.05 度的尺度不变各向异性旋转场可以将小尺度透镜功率谱 （L≳2000） 抑制在 ∑imνi=50 meV 的大质量中微子效应相当的水平，使旋转场成为未来 CMB 实验中微子质量测量中简并的重要来源。我们为这种类似 N（1）L 的噪声提供了一个解析表达式和一个基于模拟的估计器，这允许在未来的实验中有效地预测和减轻偏差。此外，我们研究了非尺度不变的旋转功率谱对重建的透镜功率谱的影响，发现小尺度旋转功率谱中的功率过大会导致更大的偏差。我们的工作提供了一个有效的数值框架，可以准确建模和解释未来 CMB 透镜测量中各向异性旋转引起的偏差。