Cosmological data probe massive neutrinos via their effects on the geometry of the Universe and the growth of structure, both of which are degenerate with the late-time expansion history. We clarify the nature of these degeneracies and the individual roles of both probes in neutrino mass inference. Geometry is strongly sensitive to neutrino masses: within ΛCDM, the primary cosmic microwave background anisotropies alone impose that the matter fraction Ωm must increase fivefold with increasing neutrino mass. Moreover, large-scale structure observables, like weak lensing of the CMB, are dimensionless and thus depend not on the matter density (as often quoted) but in fact the matter fraction. We explore the consequential impact of this distinction on the interplay between probes of structure, low-redshift distances, and CMB anisotropies. We derive constraints on the neutrino's masses independently from their suppression of structure and impact on geometry, showing that the latter is at least as important as the former. While the Dark Energy Spectroscopic Instrument's recent baryon acoustic oscillation data place stringent bounds largely deriving from their geometric incompatibility with massive neutrinos, all recent type Ia supernova datasets drive marginal preferences for nonzero neutrino masses because they prefer substantially larger matter fractions. Recent CMB lensing data, however, neither exclude neutrinos' suppression of structure nor constrain it strongly enough to discriminate between mass hierarchies. Current data thus evince not a need for modified dynamics of neutrino perturbations or structure growth but rather an inconsistent compatibility with massive neutrinos' impact on the expansion history. We identify two of DESI's measurements that strongly influence its constraints, and we also discuss neutrino mass measurements in models that alter the sound horizon.

中文翻译：

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大质量中微子和宇宙组成


宇宙学数据通过大质量中微子对宇宙几何和结构增长的影响来探测它们，这两者都会随着晚期膨胀历史而退化。我们阐明了这些简并的性质以及两种探针在中微子质量推断中的单独作用。几何学对中微子质量非常敏感：在 ΛCDM 中，仅初级宇宙微波背景各向异性就使物质分数 Ωm 必须随着中微子质量的增加而增加五倍。此外，大尺度结构可观测物，如 CMB 的弱透镜，是无量纲的，因此不取决于物质密度（经常被引用），而实际上取决于物质分数。我们探讨了这种区别对结构探针、低红移距离和 CMB 各向异性之间相互作用的相应影响。我们推导出了中微子质量的约束，而不受它们对结构的抑制和对几何结构的影响，表明后者至少与前者一样重要。虽然暗能谱仪最近的重子声学振荡数据设置了严格的界限，这主要是因为它们与大质量中微子的几何不相容性，但所有最近的 Ia 型超新星数据集都推动了对非零中微子质量的边际偏好，因为它们更喜欢大得多的物质分数。然而，最近的 CMB 透镜数据既不排除中微子对结构的抑制，也没有强烈地限制它以区分质量层次结构。因此，目前的数据表明，不需要修改中微子扰动或结构增长的动力学，而是与大量中微子对膨胀历史的影响不一致的兼容性。 我们确定了 DESI 的两项测量结果，这些测量方法强烈影响其约束条件，我们还讨论了改变声界的模型中的中微子质量测量。