发表机构
Université Libre de Bruxelles; Université Paris-Saclay, CNRS, Institut d’astrophysique spatiale（布鲁塞尔自由大学; 巴黎萨克雷大学，法国国家科学研究中心，空间天体物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
针对光锥上角双谱的压缩极限问题，提出自旋加权球谐函数解析方法，消除抵消项并改进 Limber 近似，进而推导出更简单且包含新项的 SSC，适用于未来大天区巡天。
AI 中文摘要
大尺度结构的观测位于光锥上。宇宙学统计量因此必须从三维投影到角空间。对于双谱及更高阶统计量，多谱除了依赖于傅里叶模的模长外，还关键地依赖于傅里叶模之间的夹角。这导致在压缩极限中出现微妙的抵消，并使 Limber 近似失效。这对于预测超样本协方差（SSC）是有问题的，因为目前没有已知的关于角度依赖项的全天计算。在这里，我们发展了一种新的解析方法来处理角双谱，将傅里叶矢量写为导数，将其投影到球面上，并利用自旋加权球谐函数进行处理。我们找到了无抵消的双谱方程，并且这些方程适用于超越 Limber 的数值方法。Limber 近似变得良态，并在压缩极限及任何其他构型下均有效。然后，我们推导了这一点对单点统计量（如星系团或峰值计数）与两点统计量（如星系成团、弱引力透镜或 21cm）之间协方差的影响，该协方差与压缩双谱相关。结果分为调查内协方差和 SSC，我们发现与以往文献存在显著差异。我们的结果与光锥的 2+1 几何一致，例如除了空间导数外还有时间导数。我们还发现潮汐项与更简单的仅增长项是简并的。总的 SSC 包含大量新项，包括广角效应和对背景速度的响应。然而，我们在数值上表明，它可以被一个仅密度响应的单一项很好地近似。这最终使我们的结果比以往文献更简单。这一全天结果对于大天区而言应比以往的平面天区极限更具代表性，因此对于即将到来的观测（如 Euclid、LSST 和 Roman）具有相关性。
英文摘要
Observations of the Large Scale Structure sit on the light cone. Cosmological statistics must then be projected from 3D to angular space. For the bispectrum and higher orders, the polyspectra crucially depend on the angles between Fourier modes in addition to their moduli. This leads to delicate cancellations in the squeezed limit and make Limber's approximation fail. This is problematic for predicting the Super-Sample Covariance (SSC), with no known full-sky computation of the angle-dependent terms. Here we develop a new analytical approach to the angular bispectrum, writing Fourier vectors as derivatives that we project on the sphere and tackle with spin-weighted spherical harmonics. We find bispectrum equations free of cancellations and amenable to beyond-Limber numerical methods. Limber's approximation becomes well-behaved and works in the squeezed limit and any other configuration. We then derive the consequence for the covariance between 1-point (e.g. cluster or peak counts) and 2-point statistics (e.g. galaxy clustering, weak lensing or 21cm), which relates to the squeezed bispectrum. The results split into intra-survey covariance and SSC, where we find significant differences with past literature. Our results are in line with the 2+1 geometry of the light cone, having e.g. temporal derivatives in addition to spatial ones. We also find that the tidal term is degenerate with the simpler growth-only term. The total SSC contains a wealth of new terms including wide-angle effects and responses to the background velocity. However we show numerically that it is well approximated by a single term with a density-only response. This ultimately makes our results simpler than past literature. This full-sky result should be more representative than the past flat-sky limit for large survey areas, thus being the one relevant for coming observations with e.g. Euclid, LSST and Roman.
Comments40+34 pages, 6 figures, 2 summary tables for the bispectrum, 1 summary equation for the SSC
