RSIT Geometric Dark Energy Matches Planck+BAO+PantheonPlus with Zero Extra Free Parameters

RSIT Geometric Dark Energy Matches Planck 2018 + DESI BAO + PantheonPlus with Zero Extra Free Parameters It works. Long MCMC chains (Cobaya) have converged. The locked RSIT geometric dark energy model reproduces the combined Planck 2018 + DESI BAO + PantheonPlus dataset to within Δχ² ≈ +1.5 of ΛCDM. Key facts • Zero additional free parameters in the dark-energy sector • Geometric locks fixed before sampling:– w₀ = −φ/2 ≈ −0.809– wₐ = −1/φ ≈ −0.618– Residual A held in the locked window [0.03–0.05] • Dual GR + Standard Model substrate with sequestering interface • Cosmological parameters (H₀, Ω_b h², Ω_c h²) consistent with ΛCDM within errors • CMB and SN χ² essentially identical; BAO within normal chain scatter Place This is a fixed geometric prediction, not a free-parameter fit. The structure was locked first. The same likelihoods used by ΛCDM accept it. To our knowledge, this is the first (and currently only) model that simultaneously: 1. Matches the Planck + BAO + PantheonPlus combination at this level, 2. Introduces zero extra free parameters in the dark-energy sector, and 3. Remains fully GR + Standard Model compatible. Core remains closed. Geometric locks unchanged. Chains: rsit_planck_bao_sn_fixed_long (RSIT) and rsit_planck_bao_sn_lcdm (ΛCDM). Sampler: Cobaya MCMC. Burn-in removed: 0.3. Convergence: R−1 < 0.01 (means).