[论文解读] The Atacama Cosmology Telescope: DR6 Constraints on Extended Cosmological Models

Erminia Calabrese, J. Colin Hill+170 more|ArXiv.org|Mar 18, 2025

Astronomy and Astrophysical Research被引用 10

一句话总结

ACT DR6 与 Planck 等数据联合测试扩展宇宙学模型，但未发现对 LambdaCDM 的令人信服的偏离；对中微子、基本常数以及早期/修正再组合物理的约束。

ABSTRACT

We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from Planck. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index $d n_s/d\ln k = 0.0062 \pm 0.0052$) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ($N_{ m eff} = 2.86 \pm 0.13$, which combined with external BBN data becomes $N_{ m eff} = 2.89 \pm 0.11$), for non-zero neutrino masses ($\sum m_ν< 0.082$ eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ($N_{ m idr} < 0.134$), early-universe variation of fundamental constants, early dark energy, primordial magnetic fields, or modified recombination. Our data are consistent with standard BBN, the FIRAS-inferred CMB temperature, a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant, and the late-time growth rate predicted by general relativity. We find no statistically significant preference for a departure from the baseline $Λ$CDM model. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored by our data.

研究动机与目标

• 以 ACT DR6 的高灵敏度 CMB 数据及补充数据集为基础，推进对 LCDM 框架的精密检验。
• 推导对 LCDM 广义扩展的约束，涵盖原始涨落、再组合前后物理以及晚期宇宙学。
• 评估新物理（中微子性质、暗辐射、变动常数、早期暗能量、修正再组合）是否相对于 LCDM 改善拟合。

提出的方法

• 分析 ACT DR6 主要温度与极化幂谱（TT、TE、EE），跨多个频带（f090、f150、f220）。
• 将 ACT DR6 与 Planck 传统数据、CMB 引力透镜、BAO（DESI 或 BOSS）及 SNIa（Pantheon+）结合起来，以打破参数简并。
• 使用多频似然（MFLike）和带 Planck 截断的仅 CMB 似然（ACT-lite）来纳入从大尺度到中尺度的信息。
• 对低红移 tau 先验来自 Sroll2，并在适当情况下，对易于简并的参数使用完整似然。
• 在贝叶斯框架中探索单参数扩展以及更广泛的再组合前/后物理情景。

实验结果

研究问题

• RQ1 ACT DR6 与 Planck 等数据联合是否揭示对标准 LCDM 模型的任何统计显著偏离？
• RQ2 对中微子性质（质量和有效物种数 N_eff）以及替代的早期/修正再组合作用情景的约束如何？
• RQ3 在 ACT DR6 及补充数据集的背景下，早期暗能量、原初磁场或变动基本常数的结论如何？
• RQ4 纳入 CMB 引力透镜与后期探测是否能收紧对 LCDM 偏离的限制，并影响推断的 H0 与 sigma8？

主要发现

• 在所探讨的拓展中，未发现对 LCDM 的统计上显著偏离的偏好。
• d_n_s/d ln k = 0.0062 ± 0.0052，与尺度不变的原始涨落一致。
• N_eff = 2.86 ± 0.13（结合天体物理 BBN 先验得到 N_eff = 2.89 ± 0.11），没有额外轻自由流动粒子的证据。
• 中微子质量总和 < 0.082 eV（95% 置信水平）。
• N_idr < 0.134，较不利于自相互作用暗辐射。
• 电磁精细结构常数和电子质量在早期宇宙无显著变动：α/α0 = 1.0043 ± 0.0017，me/me0 = 1.0063 ± 0.0056。
• BBN 氦分数 Yp = 0.2312 ± 0.0092；宇宙微波背景温度 T_CMB = 2.698 ± 0.016 K；暗能量方程状态 w = -0.986 ± 0.025；增长指数 γ = 0.663 ± 0.052。
• 无需 LCDM 以外的额外物理来解释 ACT DR6 结果；旨在提高 H0 或降低 sigma8 的模型在数据中不被偏好。