RCA Ω 2027 — Phase VIII: Three Falsifiable Predictions from mu-Sigma Separation and Boltzmann Validation

 Phase VIII of the Relativistic Coupling Ansatz (RCA) separates the two
  couplings beta (expansion geometry) and delta (gravitational slip) into
  independent physical channels. Delta is now the EFT-of-dark-energy
  gravitational-slip amplitude mu(z) = 1 + delta × gate(z), the same "mu"
  constrained by Planck 2018 and DESI 2024 modified-gravity analyses.

  This release archives three falsifiable predictions not present in Phase VII:

  [1] Growth-without-lensing: mu(z) > 1 while Sigma(z) ~ 1 at z=[0.16,0.40].
      Confirmed in CLASS Boltzmann code Stage B: 6.32% Weyl-power separation,
      0.00% growth spread (commit 49c209b). Survey target: DESI Y3 + Rubin LSST.

  [2] fsigma8 deficit at z=[0.10,0.40] if delta > 0. Current data miss this
      window entirely (chi2 monotone, Δchi2=-0.016). DESI Year 3 (2027-2029)
      will fill the gap with 3 points at z=0.15, 0.25, 0.35. Detection
      threshold: delta ~ 0.30 at TPR=50%.

  [3] fsigma8 sign-flip at z ~ 0.58. The deviation changes sign due to
      beta-delta competition — unique to two-channel models. No single-channel
      model produces this pattern.

  Phase XVIII MCMC (96 walkers, 15,000 steps, tau_max=123, converged):
    corr(beta,delta) = -0.052 (degeneracy broken from -1.000 in Phase VII)
    Omega_m = 0.294 ± 0.006
    H0 = 69.30 +0.37/-0.22 km/s/Mpc
    delta 95% upper bound: < 0.716 (prior-dominated; not a detection)