Relational Gravity links Ni-62 nuclear coherence to DESI DR2 BAO and ISW measurements

NOTE: This work is conceptual and exploratory. It outlines early motivations and heuristic ideas, and should not be taken as identical to the phenomenological models currently under development — including both the structural Δw approach and the scalar-field formulation used in technical perturbation and MCMC analyses. It is intended as background context rather than a formal physical model. Relational Gravity (RG) v1.2 derives late-time cosmology from quantum-gravitational degrees of freedom and nuclear binding data alone, requiring neither dark matter nor dark energy and introducing no free cosmological parameters. From laboratory physics, the model predicts a universal relativistic correction delta w = +0.070 to the weak-field gravitational potential. When compared with the DESI DR2 BAO-only anisotropic distances (Table IV, excluding BGS; DESI Collaboration 2025, DOI 10.48550/arXiv.2503.14738), the zero-parameter prediction yields chi² = 21.48 (18 degrees of freedom). A standard ΛCDM × α rescaling returns chi² = 19.40, while marginalising over delta w gives delta w = +0.051 ± 0.011 with chi² = 18.62 (Δchi² ≈ –0.8 relative to ΛCDM × α). Without any adjustment to cosmological data, the same framework accounts for the observed ISW–LSS cross-correlation excess (+12 % predicted vs. +10.8 ± 3.1 % observed) and the direction of BAO-scale compression (0.70 σ predicted vs. 0.64 σ observed; Ni et al. 2024), each matched to better than 0.4 σ. All calculations are fully reproducible. Code, environment, and notebooks are archived at DOI 10.5281/zenodo.17557630.