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| Format: | Preprint |
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2026
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| Online-Zugang: | https://arxiv.org/abs/2604.11865 |
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| _version_ | 1866915935106891776 |
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| author | Kolhatkar, Ameya Sahoo, P. K. |
| author_facet | Kolhatkar, Ameya Sahoo, P. K. |
| contents | We present a rigorous theoretical and observational analysis of the Hybrid $ f(Q) $ class of models by including the late-time modifying $ 1/Q $ term. After deriving strict viability conditions from the analytical expansion history, we show that preserving early-universe structure formation dictates that the linear coupling be exactly unity. This fixes the background of the Hybrid model into a geometric degeneracy with $ Λ$CDM which is confirmed explicitly through MCMC analysis with the latest background-only probes. The physical novelty of this model is manifest in the perturbation sector, where the geometric coupling breaks the background degeneracy and induces a late-time suppression of the effective gravitational constant $ G_{eff} < G_N $. Consequently, the inclusion of RSD data reveals an amplitude compensation mechanism, by which the matching of the signature $ fσ_8 $ of the data causes the clustering amplitude $ σ_8 $ to inflate under weaker gravity. Statistical model comparison through AIC/DIC demonstrates that incorporating growth data yields a moderate to weak preference for the Hybrid model keeping the background cosmology intact. This provides a physically bounded alternative to $ Λ$CDM with a falsifiable signature in the large scale structure, directly testable by the next generation of galaxy surveys. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_11865 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Beyond the Cosmological Constant: Breaking the Geometric Degeneracy of $ f(Q) $ cosmology via Redshift-Space Distortions Kolhatkar, Ameya Sahoo, P. K. General Relativity and Quantum Cosmology We present a rigorous theoretical and observational analysis of the Hybrid $ f(Q) $ class of models by including the late-time modifying $ 1/Q $ term. After deriving strict viability conditions from the analytical expansion history, we show that preserving early-universe structure formation dictates that the linear coupling be exactly unity. This fixes the background of the Hybrid model into a geometric degeneracy with $ Λ$CDM which is confirmed explicitly through MCMC analysis with the latest background-only probes. The physical novelty of this model is manifest in the perturbation sector, where the geometric coupling breaks the background degeneracy and induces a late-time suppression of the effective gravitational constant $ G_{eff} < G_N $. Consequently, the inclusion of RSD data reveals an amplitude compensation mechanism, by which the matching of the signature $ fσ_8 $ of the data causes the clustering amplitude $ σ_8 $ to inflate under weaker gravity. Statistical model comparison through AIC/DIC demonstrates that incorporating growth data yields a moderate to weak preference for the Hybrid model keeping the background cosmology intact. This provides a physically bounded alternative to $ Λ$CDM with a falsifiable signature in the large scale structure, directly testable by the next generation of galaxy surveys. |
| title | Beyond the Cosmological Constant: Breaking the Geometric Degeneracy of $ f(Q) $ cosmology via Redshift-Space Distortions |
| topic | General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2604.11865 |