Unified Spacetime Fluid Cosmology II: A Minimal Effective Realization of Late-Time Structure Growth with Two-Step Spacetime Friction
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2026
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| _version_ | 1866901892717608960 |
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| author | Sonoda, Ryuji |
| author_facet | Sonoda, Ryuji |
| contents | <p>This paper presents the second part of the Unified Spacetime Fluid (USF) cosmology program. Building on the background-only construction of Paper I, it develops a minimal effective growth-sector realization, USFm, in which a time-dependent spacetime-friction term X(a) modifies the linearized Euler equation of the matter flow while keeping the metric sector identical to linear General Relativity, with μ=Σ=1 and cT=1.</p> <p>The friction history is modeled phenomenologically as a two-step late-time transition and is interpreted through a theory bridge based on coarse-grained transition fractions and interface densities. The construction is tested with a compact growth-sector diagnostic based on compressed BOSS/eBOSS fσ8 measurements. The representative solution produces a mild low-redshift suppression of structure growth, Δfσ8(z) ~ -0.03 toward z → 0, while remaining observationally viable within the current simplified growth-data precision.</p> <p>The analysis should be read as a controlled phenomenological realization rather than as a full covariant microscopic completion. A fully covariant exchange-current model, microscopic origin of the momentum-exchange term, and systematic stability analysis are left for future work.</p> |
| format | Recurso digital |
| id | zenodo_https___doi_org_10_5281_zenodo_20156335 |
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| publishDate | 2026 |
| publisher | Zenodo |
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| spellingShingle | Unified Spacetime Fluid Cosmology II: A Minimal Effective Realization of Late-Time Structure Growth with Two-Step Spacetime Friction Sonoda, Ryuji Unified Spacetime Fluid USF cosmology USFm spacetime friction structure growth fσ8 redshift-space distortions BOSS eBOSS growth tension E_G ΛCDM effective theory cosmology <p>This paper presents the second part of the Unified Spacetime Fluid (USF) cosmology program. Building on the background-only construction of Paper I, it develops a minimal effective growth-sector realization, USFm, in which a time-dependent spacetime-friction term X(a) modifies the linearized Euler equation of the matter flow while keeping the metric sector identical to linear General Relativity, with μ=Σ=1 and cT=1.</p> <p>The friction history is modeled phenomenologically as a two-step late-time transition and is interpreted through a theory bridge based on coarse-grained transition fractions and interface densities. The construction is tested with a compact growth-sector diagnostic based on compressed BOSS/eBOSS fσ8 measurements. The representative solution produces a mild low-redshift suppression of structure growth, Δfσ8(z) ~ -0.03 toward z → 0, while remaining observationally viable within the current simplified growth-data precision.</p> <p>The analysis should be read as a controlled phenomenological realization rather than as a full covariant microscopic completion. A fully covariant exchange-current model, microscopic origin of the momentum-exchange term, and systematic stability analysis are left for future work.</p> |
| title | Unified Spacetime Fluid Cosmology II: A Minimal Effective Realization of Late-Time Structure Growth with Two-Step Spacetime Friction |
| topic | Unified Spacetime Fluid USF cosmology USFm spacetime friction structure growth fσ8 redshift-space distortions BOSS eBOSS growth tension E_G ΛCDM effective theory cosmology |
| url | https://doi.org/10.5281/zenodo.20156335 |