Kavli Affiliate: Masahiro Takada
| First 5 Authors: Ryo Terasawa, Masahiro Takada, Toshiki Kurita, Sunao Sugiyama,
| Summary:
The $S_8$ value inferred from the Subaru Hyper Suprime-Cam (HSC) Year 3
cosmic shear data, under the assumption of the flat $Lambda$CDM model, is
2-3$sigma$ lower than that inferred from observations of the early-time
universe, such as cosmic microwave background (CMB) anisotropy data. Resolving
the $S_8$ tension requires a scenario in which structure formation on small
scales is suppressed in the late universe. As potential solutions, we consider
extended models both within and beyond the $Lambda$CDM model — models that
incorporate parameterized baryonic feedback effects, the effect of varying
neutrino mass, and modified structure growth, each of which can lead to a
suppression of structure growth at lower redshifts, with its own distinct
scale- and redshift-dependencies. In particular, we consider phenomenological
modified gravity models in which the suppression of structure growth is
triggered at lower redshifts, as dark energy ($Lambda$) begins to dominate the
background expansion. We show that the modified growth factor models —
especially those featuring more rapid growth suppression at lower redshifts —
provide an improved fit to the combined datasets of the HSC-Y3 cosmic shear
correlation functions, the Planck CMB, and the ACT DR6 CMB lensing, compared to
the fiducial $Lambda$CDM model and the models including the baryonic effects
or the massive neutrino effect within the the $Lambda$CDM framework.
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