We present GRU (Geometría Radial Unitaria), a phenomenological framework connecting Causal Dynamical Triangulation (CDT) quantum gravity with observable predictions for LISA and Solar System tests. Version 2. 5 consolidates and closes all internal validation gaps identified in prior versions: Root Invariance Protocol (§A. 46, new): resolves the P1 validation test — confirms the causal spine is a topological invariant (S¹ cycle of T nodes), independent of representative-node choice (ds=0. 9602±0. 0413, std=0. 041<0. 05). Official fspine correction: fspine = 7. 7912 mHz, ΔtGRU = 128. 35 s, measured directly from real CDT data (N=2567, T=20), replacing prior unverified estimates. §A. 41–A. 42: MDR (Modified Dispersion Relation) framework from the Regge Hessian, honestly labeled as a phenomenological hypothesis (γ=2·ds−2=0. 0564, verified at 0. 31σ), not a first-principles derivation. §A. 43: Quantum Computing outlook — the GRU spine defines a CPTP amplitude-damping channel (4/4 tests PASS). §A. 45: Solar System compatibility — PPN parameter γPPN=1 (δγ approximately 20, 000 times below the Cassini bound), SO (3) breaking of order 10^-82 at LIGO scales (negligible). §A. 25–A. 26: V-scan robustness and toy 4D (S³×ℝ) universality check. LISA falsifiability: Afinal=1. 46×10⁻¹⁶ predicted amplitude, detectable at N=1 SMBHB event, 5σ. Spectral dimension universality is confirmed across CDT 2D, CDT 3D (real data), and toy 4D geometries: ds (spine) → 1 in all cases, with the full-to-spine dimensional gap (Δds ≈ 4) interpreted as a signature of diffusive confinement along the causal spine. All results are computed from real CDT simplicial data where available (N=2567 vertices, T=20 temporal slices) and clearly labeled as such versus toy-model illustrations. Known open problems (Ward identity / Paley-Wiener causality of the transfer function, first-principles derivation of γ from the Regge Hessian) are explicitly documented as unresolved and deferred to v2. 6, rather than concealed or forced to a false PASS. Complete computational package (67 files, Python scripts, JSON results, QC/PPN/SO3 validation suites) included for full reproducibility.
Alfredo Flores Cornejo (Thu,) studied this question.