The Big Snap - Scale-Dependent Clustering Suppression from Late-Time Dark Matter Pressure: CLASS Implementation, Validation Protocol, and First Results

This paper presents the BigSnap framework: a phenomenological effective field theory in which the observable universe crystallized in a single body-centered cubic (BCC) phase transition during the post-inflationary epoch. The scalar field driving the transition is identified with dark energy. Taking the observed BAO scale of 150 Mpc as the BCC lattice constant, the scalar field mass is uniquely determined as m = 4.27 × 10⁻³² eV. The framework carries two observationally bounded free parameters (μ < 0.1 from Planck CMB constraints, β treated as β → 0 at the EFT level). Dark matter and dark energy are not separate substances — they are different dynamical behaviors of the same scalar field. The background field sources dark energy. The excitations source dark matter. The ratio of their densities Ω_R = ρ_dm/ρ_Λ determines when the snap occurs.

BCC geometry — observational tests: Three independent observational tests of the predicted BCC geometry are reported. The Giant Arc (z ≈ 0.8, Lopez et al. 2022) aligns with a predicted BCC body diagonal direction at 3.89σ. A BCC orientation fit to the SDSS DR7 void catalog places the nearest face diagonal axis 12.6° from the CMB Cold Spot across five independent fits, with a 2,000,000-trial Monte Carlo returning p = 0.006 (2.5σ). Two independent void-finding algorithms applied to the full-sky 2MASS Redshift Survey find voids clustering toward the 12 BCC face diagonal directions at 2.2–3.3σ. Combined Fisher significance: p = 8×10⁻⁸, nominal 5.24σ. The BCC axis and harmonic wavenumber ratios are pre-committed before DESI DR2. Four explicit falsification criteria are stated in advance.

Perturbation sector — CLASS results: A CLASS Boltzmann code implementation of the dark matter pressure sector has been completed and validated. For r = 4×10⁻⁴ and γ = 1.5, the model produces σ₈ = 0.780 against the ΛCDM reference σ₈ = 0.822 (5.1% suppression), with correct late-time onset (0.0% at z=2, 5.1% at z=0). Eight validation checks passed including CMB TT (0.007% deviation), CMB lensing (0.075% deviation), fσ₈ (0.9% at z=0.5), and BAO peak (0.009% shift). A KiDS-1000 S₈ comparison yields Δχ² ≈ 13.8 improvement over ΛCDM, roughly a ~3σ-level preference after accounting for two additional parameters.

Hubble tension: The a³ scaling of the pressure term ensures w_dm ~ 10⁻¹⁵ at recombination. The sound horizon shifts by −0.015% and H₀ by 0.0000 km/s/Mpc. The Hubble tension is not addressed by this mechanism. This is a structural limitation: the same scaling that makes the CMB safe prevents any lever arm on the sound horizon.

Scope: The Version 2: Adds Layer 2 coupling mechanism with γ = 3/2 transition at z ≈ 1.8, KiDS-1000 tomographic analysis with parameter robustness scan (3.5σ → 0.6σ S₈ tension reduction), BOSS DR12 CMASS South void test (pre-committed protocol, Fisher p = 0.144 null result), and late-time field stability section. All additions include explicit limitation statements. The 5.24σ BCC geometry result and the CLASS S₈ result are independent channels from the same framework and are not statistically independent. Full likelihood analysis against combined datasets is deferred to future work.

Companion CLASS implementation paper: Snider, D., "Scale-Dependent Clustering Suppression from Late-Time Dark Matter Pressure," Zenodo (2026).

10.5281/zenodo.19864442