Testing Small-Scale Modifications in the Primordial Power Spectrum with Subaru HSC Cosmic Shear, Primary CMB and CMB Lensing

Ryo Terasawa,Masahiro Takada, Sunao Sugiyama, Toshiki Kurita

arXiv · Cosmology and Nongalactic Astrophysics（2025）

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Abstract

Different cosmological probes, such as primary cosmic microwave background (CMB) anisotropies, CMB lensing, and cosmic shear, are sensitive to the primordial power spectrum (PPS) over different ranges of wavenumbers. In this paper, we combine the cosmic shear two-point correlation functions measured from the Subaru Hyper Suprime-Cam (HSC) Year 3 data with the Planck CMB data, and the ACT DR6 CMB lensing data to test modified shapes of the PPS at small scales, while fixing the background cosmology to the flat ΛCDM model. We consider various types of modifications to the PPS shape: the model with a running spectral index, the tanh-shaped model, the Starobinsky-type modification due to a sharp change in the inflaton potential, the broken power-law model, and the multiple broken power-law model. Although the HSC cosmic shear data is sensitive to the PPS at small scales, we find that the combined data remains consistent with the standard power-law PPS, i.e., the single power-law model, for the flat ΛCDM background. In other words, we conclude that the S_8 tension cannot be easily resolved by modifying the PPS within the ΛCDM background.

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【要点】：本文通过结合 Subaru HSC 宇宙剪切数据、Planck CMB 数据以及 ACT DR6 CMB 弯曲数据，测试了原初功率谱在较小尺度上的修改，发现标准幂律形式的原初功率谱与观测数据一致，不支持通过修改原初功率谱来解决宇宙学参数 S_8 的紧张关系。

【方法】：研究使用了多种原初功率谱修改模型，包括带有运行谱指数的模型、双曲型模型、Starobinsky型修改模型、断裂幂律模型和多重断裂幂律模型，并将这些模型与宇宙剪切、CMB 各向异性及CMB 弯曲数据相结合，固定背景宇宙学模型为平坦ΛCDM模型进行测试。

【实验】：实验利用了 Subaru HSC Year 3 宇宙剪切数据、Planck CMB 数据和 ACT DR6 CMB 弯曲数据，通过分析这些数据集来限制原初功率谱的形状，最终结果表明当前数据仍支持标准幂律形式的原初功率谱。

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