The Bosonic Vacuum as a Negative-Compressibility Condensate: Tachyonic Phase Transitions, Repulsion, and Local GUT Symmetry

The paper proposes an effective field theory (EFT) in which the quantum vacuum behaves as a bosonic condensate whose compressibility can become negative near a critical point. This state leads to a tachyonic regime (meff2<0m_{\text{eff}}^{2} < 0meff2<0) and a transient repulsive gravitational response—without altering general relativity’s Einstein–Hilbert term. The framework further predicts that in extreme astrophysical environments such as black holes, neutron stars, or active galactic nuclei, environmental effects (curvature and intense gauge fields) can locally restore grand unified (GUT) symmetries, thus linking cosmological dynamics with high-energy particle physics.