Environment-Split BAO

When the BAO peak in the galaxy correlation function is measured separately in high-density and low-density environments, the inferred peak position shows a small but systematic shift: the BAO scale appears slightly different in voids compared to clusters. ΛCDM, with its constant cosmological constant, predicts no such environment dependence — the sound horizon is a universal ruler. SCT predicts exactly this split. The dynamical cosmological term Λ_eff is elevated in underdense void regions, where the local gravitational binding strength λ_local is below the cosmic mean, and suppressed in dense regions where λ_local is above average. This means the effective expansion rate since decoupling has differed between these environments, shifting the projected BAO scale in opposite directions.

Quantitatively, in the KBC Supervoid where Λ_eff exceeds the global mean by roughly 20%, the expansion since z ≈ 0.5 has been slightly faster, compressing the angular BAO scale slightly relative to what a universe with constant Λ would predict. In dense cluster environments, the suppressed Λ_eff means slightly slower expansion, stretching the projected scale in the opposite direction. The environment-split BAO signal therefore measures the spatial variation in Λ_eff directly — it is a map of the tensor mesh dissipation rate across different large-scale environments. SCT predicts the sign and approximate magnitude of this split from the known density contrast of the KBC Supervoid, offering a quantitative, falsifiable prediction that no ΛCDM variant with constant dark energy can reproduce.