Version 2.0/2.1 UpdateFollowing correspondence with Prof. Wolfgang Ketterle (MIT, Nobel Laureate 2001), this version refines the experimental focus and formalizes the cold-atom interferometry path-validation protocol as the primary empirical route for testing Ξ-EFT. It specifies the three high-sensitivity laboratory platforms suitable for falsifying the predicted decoherence plateau—levitated optomechanics, molecular interferometry, and pivoted ultracold-atom interferometry—and introduces the exclusion-curve formulation C(T)=C₀ · \exp[-(Γ_{tech}+Γ_Ξ) T]. It refines Test 2 (Molecular Interferometry) to use the Talbot–Lau visibility-floor formulation — replacing the earlier “contrast-decay vs time” model — and explicitly defines the intrinsic rate as Γ_Ξ ≈ κ / (m σ²). The change improves conceptual realism and experimental feasibility while leaving the overall framework and other tests unchanged. -------------------------------------------------------------------------------------------------------------------- This white paper presents Ξ-EFT (Xi Effective Field Theory), a framework introducing a dimensionless field Ξ that interpolates continuously between quantum (Ξ = 0) and gravitational (Ξ = 1) behavior. The theory predicts a falsifiable bridge between coherence and curvature—a measurable decoherence plateau governed by the Kappa–Sigma (κ–σ) law: Γ_F ≈ (κ ħ)/(m σ²) where Γ_F is the Fisher-induced decoherence rate, m the mass, σ the spatial width, and κ a dimensionless coupling analogous to α or G. Three laboratory platforms are already capable of testing this prediction: Levitated optomechanics — coherence-time plateau at Γ_env ≈ 10⁻⁸ s⁻¹ Molecular interferometry — visibility floor under ultra-high vacuum ⁸⁷Rb BEC free expansion — width saturation against ballistic growth Synthetic verification (10⁶ trajectories) confirms the 1/σ² scaling (R² ≈ 0.999) and on-shell energy-momentum conservation. Observation of any plateau, floor, or saturation at the predicted thresholds would constitute direct empirical evidence for a continuous field linking quantum decoherence and gravitational dynamics; absence would falsify Ξ-EFT. Annex A provides a fully reproducible Python notebook that generates the four reference figures in < 5 minutes, establishing a self-contained benchmark for independent replication.