Cosmo-26

"CoDE-4: A Phenomenological Framework for Cross-Epoch Cosmological Consistency"

Not scheduled

15m

Gorlaeus gebouw (Leiden University)

Poster

Speaker

Siddharth Sathish Kumar (Independent Researcher)

Description

CoDE-4 (Cosmic Dynamical Expansion Framework v1.0)

Cross-Epoch Consistent Resolution of the H₀ Tension with Coupled Expansion–Growth Dynamics

Model Status and Scope

CoDE-4 is a phenomenological cosmology framework designed to test whether modest early-time expansion modifications combined with scale-dependent structure-growth coupling can reconcile the Hubble-parameter discrepancy while preserving observational consistency from recombination to late-time large-scale structure.

The present release represents a validated baseline implementation rather than a finalized cosmological theory. As with all precision cosmology frameworks, parameters are expected to evolve as constraints improve from next-generation surveys.

Planned updates will incorporate:

• Euclid large-scale structure mapping
• Roman Space Telescope supernova distances
• DESI final BAO catalogues
• CMB-S4 acoustic constraints
• JWST high-redshift galaxy statistics

All revisions will be version-tracked and released through the public repository.

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Observational Alignment (v1.0 Validation Suite)

CoDE-4 demonstrates simultaneous agreement with 14 independent observational regimes:

Early-Universe Geometry

✔ Planck acoustic scale θ*
✔ First acoustic peak position ℓ₁
✔ CMB shift parameter R
✔ damping-tail expansion consistency
✔ Big-Bang nucleosynthesis expansion rate
✔ matter–radiation equality redshift

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Expansion History

✔ BAO distance scale D_V(z)
✔ Pantheon Type-Ia supernova luminosity distances
✔ comoving distance to recombination
✔ sound-horizon calibration

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Structure Formation

✔ redshift-space distortion growth f\sigma_8(z)
✔ growth index γ evolution
✔ Integrated Sachs–Wolfe potential decay
✔ matter power-spectrum turnover scale
✔ weak-lensing clustering parameter S_8

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Early Galaxy Formation

✔ improved high-redshift structure timing consistent with
JADES-GS-z14-0 formation constraints

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Expansion-Rate Tension Resolution

The framework reduces the early- vs late-Universe Hubble discrepancy from

4.89\sigma \rightarrow 0.17\sigma

with

H_0 = 72.86\ \mathrm{km\,s^{-1}\,Mpc^{-1}}

while preserving CMB acoustic geometry.

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Methodological Contribution

Unlike early-dark-energy scenarios that modify only the background equation of state, CoDE-4 introduces a dual-mechanism structure:

(1) early-time expansion modification (ε-coupling)
(2) scale-dependent perturbation-growth enhancement (β-coupling)

This combined approach allows the expansion history and structure-formation timeline to adjust simultaneously without degrading recombination-era observables.

The numerical framework integrates:

• modified Friedmann evolution with early-time coupling terms
• second-order perturbation growth solver with effective gravity scaling
• cross-epoch validation spanning recombination → BAO → weak lensing → structure growth

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Model Philosophy

CoDE-4 is designed as an adaptive phenomenological framework rather than a fixed parameter solution. As observational constraints improve, parameters will be iteratively refined with fully reproducible releases.

All implementations are open-source and publicly version-tracked.

Peer validation is invited.

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Scientific Motivation

The ≈5σ discrepancy between early-Universe (Planck CMB) and late-Universe (SH0ES) determinations of H_0 represents one of the primary tensions in precision cosmology.

CoDE-4 demonstrates that modest early-time expansion modifications, when jointly constrained across recombination geometry, expansion history, and structure growth observables, can reconcile this discrepancy without degrading agreement with established datasets.

Methodology:

The framework integrates: (1) self-consistent Friedmann integration with early-time coupling terms, (2) coupled perturbation growth solver with modified effective gravity, (3) comprehensive cross-epoch validation suite spanning CMB geometry → structure formation → weak lensing.

Code & Reproducibility

MIT-licensed implementation available at:

https://github.com/siddharthatresearch-afk

Includes:

• full solver pipeline
• validation suite
• observational consistency tests
• reproducible parameter configuration