Derives exactly the density-dependent coupling κ (ρ) deferred in Paper 16. The result diverges at ρc and vanishes at infinity. Shows this divergence is intrinsic to L∝φ^1/2: the tachyon tension T (φ) =T₀φ^-1/2 diverges at the vacuum φ=0, making ρc a critical point analogous to a second-order phase transition. The hard threshold is not imposed — it emerges from the non-analytic structure of the Lagrangian. Verified with SymPy. All predictions of Paper 16 unchanged.
Marc López Sánchez (Sun,) studied this question.