A Geometric Axion at 0.392 MeV: Testable Pre- diction from Vacuum Topology

We predict a neutral pseudoscalar particle at 0.392 ± 0.001 MeV derived from 3-manifold vacuum topology. Using the Knot-Standard Model Unification (KSAU) framework—synchronized with the Standard Model Top-quark anchor ($R^2 = 0.9998$)—we identify the $6_3$ knot as the unique, mathematically minimal candidate for a CP-invariant, color-neutral dark sector boson. Key Predictions - Mass: 0.392 ± 0.001 MeV (SSoT v6.0 Synced) - Decay: $a \to \gamma\gamma$ (topologically suppressed two-photon emission) - Lifetime: $10^{-6}$ to $10^{-3}$ seconds (conservative range) - Topology: $6_3$ knot (Hyperbolic Volume $V \approx 5.6930$, $CS = 0$) Experimental Targets 1. Nuclear Transitions: Monochromatic gamma-ray anomalies around 0.392 MeV. 2. Reactor Anomalies: Excess cooling or photon flux in the 0.4 MeV window. 3. Beam Dump Experiments: Displaced vertices from long-lived neutral decays into $\gamma\gamma$ with invariant mass $\approx 0.39$ MeV. Unlike broad-range Axion-Like Particle (ALP) searches, this topological derivation provides a definitive monochromatic target at 0.392 MeV. Discovery would confirm the geometric origin of fundamental mass and the discrete nature of the quantum vacuum. Complete theoretical framework: doi.org/10.5281/zenodo.18521244 (https://doi.org/10.5281/zenodo.18521244) (Refer to v6.9 Definitive Edition for the Synchronized Mass Law derivation)