ISW-Galaxy Cross-Correlation Low

The cross-correlation of CMB temperature maps with foreground galaxy catalogs is a direct probe of the Integrated Sachs-Wolfe effect, and its amplitude in ΛCDM is fixed by the rate at which large-scale gravitational potentials decay under the influence of dark energy. Multiple independent analyses have found that the measured cross-correlation amplitude lies systematically below the ΛCDM prediction, particularly on angular scales corresponding to supervoid structures at z < 0.5. SCT provides a natural explanation: because the dynamical cosmological term Λ_eff is elevated inside the KBC Supervoid relative to ΛCDM's constant Λ, photons traversing the supervoid gain less energy than ΛCDM predicts, not more. The supervoid's gravitational potential is shallower than standard perturbation theory anticipates once the enhanced local expansion rate is properly accounted for.

Simultaneously, SCT's gravitational superposition effect in dense regions suppresses the potential decay rate in clusters and walls, reducing their ISW contribution to the cross-correlation. The net result is a cross-correlation amplitude that is generically lower than ΛCDM predicts on the scales dominated by the void-filament contrast. The apparent discrepancy is therefore not a statistical fluctuation but a systematic consequence of SCT's spatially varying Λ_eff: denser environments expand more slowly and contribute less ISW signal, while the supervoid expands faster but with shallower potentials, both effects conspiring to reduce the total cross-correlation below the ΛCDM prediction from a constant vacuum energy density.