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Exploring the Growth-Index (γ\gamma) Tension with Λs\Lambda_{\rm s}CDM

Mar 17, 2025
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Abstract: (arXiv)
Recent observational analyses have revealed a significant tension in the growth index γ\gamma, which characterizes the growth rate of cosmic structures. Specifically, when treating γ\gamma as a free parameter within Λ\LambdaCDM framework, a combination of Planck and fσ8 f\sigma_8 data yields γ≈0.64\gamma \approx 0.64, in ∼4σ\sim4\sigma tension with the theoretically expected value γ≈0.55\gamma \approx 0.55 (assuming general relativity). This discrepancy, closely related to the S8 S_8 tension, poses a new challenge to the standard cosmological model by suggesting that it predicts an excessive growth of structure. In this work, we demonstrate that the Λs\Lambda_{\rm s}CDM framework (featuring a rapid sign-switching cosmological constant (mirror AdS-to-dS transition) in the late universe at redshift z†∼2 z_\dagger \sim 2 ) can simultaneously alleviate the γ \gamma , H0 H_0 , and S8 S_8 tensions. We also examined a scenario with fixed z†=1.7 z_\dagger = 1.7 , previously identified as a sweet spot for alleviating multiple major cosmological tensions (including those in H0 H_0 , MB M_B , and S8 S_8 ) finding that it completely eliminates both the γ \gamma and H0 H_0 tensions, although it is statistically disfavored by our dataset combinations. Our findings suggest that Λs\Lambda_{\rm s}CDM is a promising model, providing a potential unified resolution to multiple major cosmological tensions.
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  • 16 pager, 4 figures, 3 tables
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