ECTI-P vs ΛCDM — Full Likelihood (CLASS + Cobaya) FAIR Comparison with Planck 2018, Pantheon+, DESI BAO, RSD, and KiDS-1000

Update v1.1:- Added modified CLASS implementation (classy_ecti_bgonly)This dataset contains the full-likelihood (CLASS + Cobaya) results for a FAIR comparison between ΛCDM and the ECTI-P model.

Key results (MAP):- Δχ² = −15.69 (ECTI − ΛCDM)- H₀: 70.91 vs 67.94 km/s/Mpc- S₈: 0.812 vs 0.829

ECTI-P is a late-time, background-only deformation of ΛCDM, designed to modify the expansion history at low redshift (z ≲ 0.5) while preserving early-time physics and CMB constraints.

The improvement in χ² is primarily driven by Type Ia supernovae, with additional contribution from weak lensing, while BAO and RSD remain statistically consistent and the CMB likelihood is not degraded.

The model is implemented as a hybrid extension:- Modified background expansion (ECTI-P)- Standard ΛCDM perturbation sector

This release includes MCMC chains, covariance matrices, configuration files, and logs used to produce the reported results.

For full details and figures, see the associated GitHub repository:https://github.com/f-patellis/ECTI-P_CLASS_fullprobe_vs_LCDM