[论文解读] Updated Constraints on Infrared Cutoff Models and Implications for Large-Scale CMB Anomalies

Ujjwal Upadhyay, Yashi Tiwari+1 more|arXiv (Cornell University)|Feb 18, 2026

Cosmology and Gravitation Theories被引用 0

一句话总结

该论文重新评估若干红外截止(IR)原始功率谱模型，使用最新的CMB、BAO和SNIa数据，未发现IR截止情形在统计上显著优于标准幂律谱；并考察对再电离与大尺度CMB异常的影响。

ABSTRACT

The nearly scale-invariant primordial power spectrum provides the standard initial conditions for cosmological perturbations. However, the largest scales remain only weakly constrained by CMB observations, leaving room for deviations such as an infrared (IR) cut-off. This possibility is further motivated by the persistence of large-scale CMB anomalies, most notably the low quadrupole power. In this work, we revisit several broad classes of phenomenologically motivated IR cut-off scenarios using parametrised functional forms of the primordial power spectrum. We confront these models with the latest CMB, BAO, and supernova data and derive updated constraints on the cut-off scale and associated features. Our results remain consistent with earlier studies, showing that although such models suppress power at low multipoles, the improvement in fit is marginal and does not overcome the associated parameter penalties. We therefore find no statistically significant evidence favouring IR cut-off models over the standard power-law spectrum with current data. We further explore the interplay between IR cut-off features and a possible increase in the reionisation optical depth, motivated by the recent CMB-BAO tension highlighted by DESI DR2 within the $Λ$CDM framework. We show that the additional freedom introduced by large-scale suppression is generally insufficient to support a substantial increase in optical depth, owing to the weak statistical preference for suppressed large-scale temperature power. Finally, we examine the implications of IR cut-off models for large-scale CMB anomalies by analysing the corresponding anomaly statistics within a Bayesian framework.

研究动机与目标

• 在原始功率谱中探索大尺度特征以解释约束较弱的IR尺度与CMB异常的潜在原因的动机。
• 在贝叶斯框架内，使用最新的CMB、BAO和SN数据约束一组表型IR截止模型。
• 通过允许更高的再电离光学深度来评估IR截止特征是否能缓解CMB–DESI张力。
• 在贝叶斯方法框架下，研究IR截止模型对大尺度CMB异常统计量，特别是四极（C2）和极性对称性的影响。

提出的方法

• 定义若干IR截止原始功率光谱（PL、EC、SB、ESB、RD）及其特征参数。
• 使用CLASS计算CMB谱、Cobaya进行采样，进行贝叶斯参数估计和模型比较（MCMC）。
• 利用Planck低l TT/EE、Planck+ACT+SPT高l、PR4透镜、DESI DR2 BAO与PantheonPlus SN数据，以及多数据集组合。
• 通过最优拟合的卡方和赤池信息准则(AIC)来评价模型性能，以惩罚额外参数。
• 在近似贝叶斯框架中，通过推导给定数据的后验分布来分析异常统计量（C2四极与奇偶性P）。
• 报告对截止尺度kc的约束及其对低-lCMB谱的影响，指出kc为上界且对较小尺度的约束较弱。

Figure 1 : Primordial power spectra for the different IR cutoff scenarios discussed in Sec. 2 , shown alongside the reference power-law spectrum (black dashed) for comparison. The vertical line marks the scale $k_{h}=2.25\times 10^{-4}\,\mathrm{Mpc}^{-1}$ , corresponding to the horizon scale of the

实验结果

研究问题

• RQ1 与标准幂律PPS相比，IR截止模型在拟合当前宇宙学数据方面是否提供统计显著的改进？
• RQ2 Planck、ACT、SPT、DESI DR2、PantheonPlus对所考察模型中的IR截止尺度kc及相关特征有何约束？
• RQ3 在ΛCDM框架内，IR截止特征能否通过允许更高的再电离光学深度来缓解CMB–BAO张力？
• RQ4 IR截止模型在贝叶斯分析中如何影响大尺度CMB异常统计量，如四极功率与奇偶不对称性？
• RQ5 相对于幂律情形，是否有IR截止模型在模型选择标准(AIC)下更受青睐？

主要发现

• 所有IR截止模型的拟合结果与幂律模型相当，对IR截止没有强统计偏好。
• 截止尺度kc的上限在CMB数据下通常更严格，而对最大尺度的约束仍然较弱。
• SB和RD在ΔAIC意义下与幂律模型统计上相当，而EC与ESB因增加了参数而略微不利。
• 对于RD模型，截止被推动到超出当前可观测宇宙视界的尺度，使观测谱与幂律情形几乎不可区分。
• IR截止引起的对小尺度的振荡振幅低于当前观测灵敏度，对改进拟合的贡献有限。
• 由于数据中缺乏对大尺度显著抑制的强信号，IR截止特征并不能通过显著提高再电离光学深度来解决CMB–BAO差异。

Figure 2 : Constraints on IR-cutoff models using the full CMB dataset and the likelihood combinations listed in Table 1 . The standard $\Lambda$ CDM model with a power-law primordial spectrum is also shown for comparison.