发表机构
University of California, Davis; University of Manchester; University of Edinburgh（加州大学戴维斯分校; 曼彻斯特大学; 爱丁堡大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过修改玻尔兹曼代码并分析CMB数据，首次限制早期宇宙小尺度电子密度涨落，发现无证据支持，且此类涨落无法有效解决哈勃常数张力问题。
AI 中文摘要
对于宇宙微波背景（CMB）所解析的尺度更小的早期宇宙，我们知之甚少，而在许多LCDM的扩展模型中，预期在千秒差距到百万秒差距尺度上存在电子密度涨落。这些涨落尽管如此，仍在CMB上留下两种印记。它们加速了再复合过程，这是先前约束以及提高推断的哈勃常数$H_0$提议背后的效应。通过沿视线方向的相关性，它们还降低了有效的汤姆逊散射率，从而增强了扩散阻尼，其增强量随相干长度增大而增大。我们在修改后的玻尔兹曼代码classito中实现了这两种效应，并使用来自Planck、ACT DR6和SPT-3G D1的CMB数据，首次对包含这种修改后光子输运的此类涨落设置了限制。我们没有发现它们的证据：电子密度对比度的方差低于$0.21$（$95\\%$置信水平），对于$2\\,{\rm Mpc}$的相干长度，该值降至$0.033$，我们以$1\\,{\rm Mpc}^{-1}\lesssim k\lesssim10^2\\,{\rm Mpc}^{-1}$范围内的电子功率谱形式给出了这些限制。我们还重新评估了小尺度电子密度涨落作为哈勃常数张力的一种解决方案。在Planck数据中，输运效应与加速再复合部分简并，拓宽了允许的$H_0$范围：结合距离阶梯先验，Planck给出$H_0 = 71.1\pm0.7\\,{\rm km\\,s^{-1}\\,Mpc^{-1}}$，并且相对于LCDM拟合有所改善。ACT和SPT-3G打破了这种简并，主要通过阻尼尾部的温度与$E$模式相关性，并且在相同的先验下，它们仅给出$H_0 = 69.3\pm0.5\\,{\rm km\\,s^{-1}\\,Mpc^{-1}}$，且相对于LCDM没有偏好。利用我们的处理方法和公开可用的代码，产生小尺度电子密度涨落的模型可以通过它们预测的方差和相干长度直接与CMB数据进行比较。
英文摘要
Little is known about the early universe on scales smaller than those resolved by the cosmic microwave background (CMB), where electron density fluctuations on kiloparsec to megaparsec scales are expected in many extensions of LCDM. These fluctuations nonetheless leave two imprints on the CMB. They accelerate recombination, the effect behind previous constraints and proposals to raise the inferred Hubble constant, $H_0$. Through correlations along the line of sight, they also reduce the effective Thomson scattering rate, enhancing diffusion damping by an amount that grows with their coherence length. We implement both effects in a modified Boltzmann code, classito, and use CMB data from Planck, ACT DR6, and SPT-3G D1 to place the first limits on such fluctuations that include this modified photon transport. We find no evidence for them: the variance of the electron density contrast is below $0.21$ ($95\%$ CL), falling to $0.033$ for a coherence length of $2\,{\rm Mpc}$, and we present these limits in terms of the electron power spectrum at $1\,{\rm Mpc}^{-1}\lesssim k\lesssim10^2\,{\rm Mpc}^{-1}$. We also reassess small-scale electron density fluctuations as a resolution of the Hubble tension. In Planck data the transport effect is partially degenerate with accelerated recombination, widening the range of $H_0$ allowed: combined with a distance-ladder prior, Planck gives $H_0 = 71.1\pm0.7\,{\rm km\,s^{-1}\,Mpc^{-1}}$ and an improved fit relative to LCDM. ACT and SPT-3G break this degeneracy, chiefly through the temperature--$E$-mode correlation in the damping tail, and with the same prior they give only $H_0 = 69.3\pm0.5\,{\rm km\,s^{-1}\,Mpc^{-1}}$ and no preference over LCDM. With our treatment and publicly available code, models that generate small-scale electron density fluctuations can be directly confronted with CMB data through the variance and coherence length that they predict.
Comments34 pages, 14 figures including appendices; code available at https://github.com/gplynch619/classito . Comments welcome!
