[论文解读] The Ups and Downs of Early Dark Energy solutions to the Hubble tension: a review of models, hints and constraints circa 2023

Vivian Poulin, Tristan L. Smith+1 more|arXiv (Cornell University)|Feb 17, 2023

Cosmology and Gravitation Theories被引用 14

一句话总结

本文综述为解决哈勃张力而提出的早期暗能量（EDE）模型，回顾其表观学与数据约束（Planck、BAO、SN1a、ACT、SPT），并讨论理论与观测挑战及未来测试前景。

ABSTRACT

We review the current status of Early Dark Energy (EDE) models proposed to resolve the "Hubble tension", the discrepancy between "direct" measurements of the current expansion rate of the Universe and "indirect measurements" for which the values inferred rely on the $Λ$CDM cosmological model calibrated on early-universe data. EDE refers to a new form of dark energy active at early times (typically a scalar-field), that quickly dilutes away at a redshift close to matter-radiation equality. The role of EDE is to decrease the sound horizon by briefly contributing to the Hubble rate in the pre-recombination era. We summarize the results of several analyses of EDE models suggested thus far in light of recent cosmological data, including constraints from the canonical {\it Planck} data, baryonic acoustic oscillations and Type Ia supernovae, and the more recent hints driven by cosmic microwave background observations using the Atacama Cosmology Telescope. We also discuss potential challenges to EDE models, from theoretical ones (a second "cosmic coincidence" problem in particular) to observational ones, related to the amplitude of clustering on scales of $8h$/Mpc as measured by weak-lensing observables (the so-called $S_8$ tension) and the galaxy power spectrum from BOSS analyzed through the effective field theory of large-scale structure. We end by reviewing recent attempts at addressing these shortcomings of the EDE proposal. While current data remain inconclusive on the existence of an EDE phase, we stress that given the signatures of EDE models imprinted in the CMB and matter power spectra, next-generation experiments can firmly establish whether EDE is the mechanism responsible for the Hubble tension and distinguish between the various models suggested in the literature.

研究动机与目标

• 总结哈勃张力以及通过在再结合前的瞬时能量密度来解决问题的EDE方式。
• 审查主要的EDE模型类别及它们的理论动机与参数。
• 评估Planck、BAO、SN1a、ACT与SPT数据如何约束EDE及其对H0及其他观测量的影响。
• 讨论EDE面临的理论与观测挑战（第二次巧合问题、S8张力、BOSS数据等）及未来前景。

提出的方法

• 将EDE模型按势能形状、动力学机制与耦合进行分类。
• 描述EDE的背景与扰动演化及其对 Weyl 势、CMB 与物质幂谱的影响。
• 将EDE预测与Planck、BAO、SN1a及高l数据进行比较；报告相对于ΛCDM的Δχ^2。
• 总结关于类似轴子的EDE（axEDE）及其在Planck与SH0ES数据中的变体分析，包含极化。
• 讨论诸如与ΛCDM及晚期宇宙学的简并性等局限性，并引入模型扩展以解决不足。

实验结果

研究问题

• RQ1 领先的早期暗能量模型及其在再结合前的瞬时能量密度机制是什么？
• RQ2 Planck、BAO、SN1a、ACT与SPT数据如何约束EDE参数并影响推断的H0？
• RQ3 EDE模型是否在不引入对其他观测量无法克服的矛盾（如S8、BOSS等）的情况下缓解哈勃张力？
• RQ4 EDE面临的主要理论与观测挑战是什么？扩展或替代形式能否解决它们？

主要发现

• EDE模型通常需要在z约1000–10000附近达到最大分数能量密度约10%来提高H0。
• 当拟合Planck、BAO和SN1a数据时，EDE可以改善与SH0ES的一致性并给出比ΛCDM更高的H0，Δχ^2 表明对 SH0ES 的拟合更好，对 Planck 的拟合略好。
• 多项分析显示EDE可将H0接近SH0ES约2σ，但与晚期结构增长（S8）及星系功率谱数据的矛盾仍然存在。
• ACT数据中讨论了EDE的线索，SPT数据影响约束；总体结果尚无定论，取决于数据组合与极化信息。
• 本综述强调理论挑战（第二次宇宙巧合问题、精细调谐）与观测矛盾（S8、BOSS、宇宙年龄），并指出未来实验（Simons Observatory、CMB-S4）可决定性地测试EDE信号。
• 尚无单一EDE模型被明确偏好；下一代数据对确认或否定EDE作为解决哈勃张力的方案至关重要。