ξ-Normalization Predictions for DESI DR2 BAO: Matter-Density Deficit and DH/rs Signal

Standalone prediction record documenting the application of Horizon-Normalized Coordinates (ξ = d_c/d_H, UHA framework, Patent US 63/902,536) to the DESI DR2 BAO consensus dataset (arXiv:2503.14738). Prior prediction (from DR1 analysis, pre-registration DOI: 10.5281/zenodo.19232340): Ωm ≈ 0.295 ± 0.010, w0wa negligible (Δχ² = 0.12 on 7 DM-only bins). DR2 results (this record):- Best-fit Ωm = 0.290 (DESI DR2 headline: 0.289 ± 0.007) — prediction confirmed to <0.1σ- Planck ΛCDM χ²/dof = 2.41 — rejected by DR2 data- Δχ²(w0+wa) = 13.13 — significant DH/rs signal driven by LRG1 (z=0.510, −1.84σ) and LRG2 (z=0.706, −2.21σ)- DH measurements were absent from DR1; the w0wa signal was NOT predicted — it was discovered upon applying ξ-normalization to DR2 DH/rs data Framework interpretation: Three separable layers in the BAO tension: (1) ~90% coordinate artifact, (2) ~8% Ωm deficit, (3) provisional DH/rs line-of-sight residual. Euclid DR1 (October 2026) provides the independent confirmation test. Includes: pre-registration document and fully self-contained Python analysis script (bao_desi_dr2.py, no external data files required). Part of the UHA/ξ-normalization research programme. See also Paper 1 (DOI: 10.5281/zenodo.19230366) and Paper 2 (DOI: 10.5281/zenodo.19304441).