宇宙微波背景B模偏振与法拉第旋转的互相关：原初磁场的新型探针
Cross-correlation between CMB B-modes and Faraday Rotation as a Novel Probe of Primordial Magnetic Fields
- Kavli IPMU (WPI), UTIAS, The University of Tokyo（木下浦和宇宙物理研究所（世界顶级学术前沿中心），多伦多大学天体物理与空间科学系，东京大学）
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge（剑桥大学应用数学与理论物理系）
- Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究提出利用CMB B模与法拉第旋转角的交叉双谱作为原初磁场的新探针，该双谱对磁场螺旋度敏感，未来实验可探测亚纳高斯振幅的磁场。
AI中文摘要：
我们研究了宇宙微波背景（CMB）B模偏振与两个法拉第旋转（FR）角之间的交叉双谱，作为原初磁场（PMFs）的一种新型探针。假设PMFs为高斯分布且包含非螺旋和螺旋分量，我们推导了Bαα双谱，并将其分解为宇称偶和宇称奇贡献。混合的非螺旋-螺旋贡献出现在宇称偶部分，而纯非螺旋和纯螺旋贡献则贡献于宇称奇部分。这种宇称依赖性提供了对PMF螺旋度的敏感度，而单独的FR功率谱则缺乏这种敏感度。随后，我们预测了SO-like和LiteBIRD-like CMB实验对该交叉双谱的可探测性，发现未来的观测可以探测到振幅在亚纳高斯（sub-nG）水平的PMFs。Bαα双谱由对螺旋度敏感的宇称偶部分主导，为约束PMFs的振幅和螺旋度提供了一条有前景的途径。
英文摘要：
We investigate the cross-bispectrum between the cosmic microwave background (CMB) $B$-mode polarization and two Faraday rotation (FR) angles as a new probe of primordial magnetic fields (PMFs). Assuming Gaussian PMFs with both non-helical and helical components, we derive the $Bαα$ bispectrum and decompose it into parity-even and parity-odd contributions. The mixed non-helical--helical contribution appears in the parity-even sector, whereas the purely non-helical and purely helical contributions contribute to the parity-odd sector. This parity dependence provides sensitivity to PMF helicity that is absent in the FR power spectrum alone. We then forecast the detectability of the cross-bispectrum for SO-like and LiteBIRD-like CMB experiments, and find that future observations can probe PMFs with amplitudes at the sub-nG level. The $Bαα$ bispectrum is dominated by the helicity-sensitive parity-even sector and provides a promising avenue for constraining both the amplitude and helicity of PMFs.
