Particles as Vacuum-Supported Modes: Higgs-Vacuum Fixation, Yukawa Selectivity, and Neutrino Coherence in the ECI Model

This work develops the Endothermic-Cold Interpretation (ECI) as a vacuum-based ontology of elementary particles and gravitation. The Higgs vacuum is treated as a physical medium with finite rigidity, while elementary particles are interpreted as localized, phase-coherent vacuum-supported modes rather than fundamental point-like objects. In this picture, mass measures the depth and stiffness of Higgs-vacuum fixation, and Yukawa couplings are reinterpreted as spectral compatibility conditions between fermionic regimes and the scalar vacuum response.A variational analysis is used to motivate a critical Yukawa scale ycrit ~ O(1), associated with the boundary of stable localized vacuum response. A complementary linear-response formulation shows that admissible Yukawa values arise from the solvability condition mH² = y²χmed(0; μ), where χmed is the renormalized fermionic susceptibility. This provides a physical interpretation of the sparsity and closure of the fermionic spectrum, with the top quark identified as a near-critical boundary mode of Higgs-vacuum fixation. An ontological classification table is introduced to organize fermions, gauge bosons, and the scalar sector according to the depth of Higgs-vacuum fixation, type of vacuum response, and degree of localization.The neutrino sector is treated as the marginal limit of vacuum fixation. Its extremely small effective mass scale naturally leads to weak localization, large mixing, sensitivity to coherence effects, and the possibility of vacuum-controlled Dirac–Majorana regimes. Three tests are formulated: an atmospheric-neutrino coherence test based on Super-Kamiokande data, a CMB phase-shift test of neutrino free streaming at recombination, and a structural Yukawa-hierarchy test of fermionic spectral closure. The atmospheric-neutrino test gives a null result for the additional phase parameter, ε ≃ 0, while an effective decoherence term improves the agreement with the public Super-Kamiokande binned data for both normal and inverted ordering. The CMB phase-shift test yields a non-zero phase-shift amplitude close to the Standard Model value, supporting free-streaming neutrino behavior at recombination. The Yukawa-hierarchy test identifies the observed fermionic spectrum as a sparse and closed sequence of admissible Higgs-vacuum fixation regimes, with the top quark lying near the critical boundary.The proposed model does not modify the formal structure of the Standard Model or General Relativity. Rather, it offers an ontological interpretation in which mass, particle stability, Yukawa hierarchy, neutrino coherence, antimatter, the non-fixed status of the photon, and gravitational response arise from a common vacuum-structure principle. Its falsifiability is tied to structural constraints: invariant particle rest masses, weak neutrino fixation, CMB free streaming, Yukawa sparsity, the limiting role of the top sector, the non-fixed status of the photon, and observable vacuum response in strong-gravity regimes.