The Plenum Paradigm: A Phenomenological Framework for Variable Vacuum Coupling and its Cosmological Implications

We propose a theoretical framework in which the universe is described as a continuous fundamental medium (the "Plenum"), saturated with quantum fields and zero-point energy. Contrary to standard approaches treating the vacuum as a passive stage, we introduce a Plenum Coupling Index (PCI) κ ∈ [0,1] as a dynamic degree of freedom, modeled by a complex scalar field Ψ obeying Ginzburg-Landau dynamics. Baryonic matter corresponds to the condensed state κ = 1, while decoupled entities (κ = 0) emerge as topological excitations of the field Ψ. In this paradigm, the speed of light c is not a fundamental constant but an emergent property of the Plenum. We show that the transition κ = 1 → κ = 0 preserves energy conservation via storage in field gradients and a topological gauge field. Causality is preserved by the degeneracy of the effective metric at κ = 0, which transforms the evolution equation from hyperbolic (Lorentzian) to elliptic (Euclidean), suspending local causality without violating it. The framework predicts stable topological modes (dark matter candidates) with effective cross-section σ ~ 10⁻⁸³ cm², resolving three ΛCDM anomalies. The plenum Higgs mechanism gives mass to the topological gauge field: m_A = q·κ₀. The optimized "Plenum-Higgs" model identifies κ₀ with the electroweak VEV (246 GeV) via Higgs-portal coupling, and derives the relaxation scale E_Plenum ~ 2.3 meV through a seesaw relation Λ₀ ~ κ₀⁴/M_Planck³, predicted within a factor of 2. We formulate fifteen falsifiable predictions testable in the 2025–2035 decade, seven of which are unique to the Plenum.