Density-Dependent Vacuum Bubble Nucleation in Matter-Coupled Dark-Sector Cosmology: Dark-Matter Granularity, Wall Dynamics and Transmission

Version 3 (language edit). Can a declining dark-matter density switch on the decay of a vacuum? For a scalar whose coupling to dark matter is centred on a false vacuum, the mean-field effective potential becomes metastable below a degeneracy density. For a vacuum at the dark-energy scale the field's Compton length is about 0.07 mm and the dark-matter energy inside a Compton volume is only 0.05 m_phi^4. Spatially resolved tests (the static field around discrete sources, the first-order decay rate with random sources, and nonperturbative bounces around a single source and a row of sources) indicate that discrete dark-matter sources suppress the decay far less than the mean field predicts, so particle dark matter leaves the vacuum close to its zero-density rate within this model. The mean field holds for wave dark matter between about 3 meV and 0.25 eV, which a 1+1-dimensional simulation of a wall running through such dark matter confirms. The decay is then environmental: voids first, galactic halos keep the held vacuum. The walls run away; dark matter crossing them gains the sudden-crossing energy and is kicked forward at about three quarters of the speed of light. Version 3 merges a professional language edit (American spelling, punctuation, word choice; the physics is unchanged). New in v2: resolved granularity tests, nonperturbative and multisource bounces with convergence checks, the 1+1D wave-dark-matter wall, evolving void contrasts, the viable region in physical parameters, and an optional neutrino coupling with its approximate CMB bound. Prepared for Physics of the Dark Universe.