The late Integrated Sachs-Wolfe (ISW) effect should produce a measurable positive cross-correlation between CMB temperature maps and tracers of large-scale structure. Many galaxy and void-based measurements find amplitudes lower than or only marginally consistent with the standard ΛCDM prediction (Crittenden & Turok 1996; Granett 2008; Fang 2019). The persistent low signal complicates dark-energy and growth-of-structure interpretations.
The standard model assumes constant Λ produces a uniform spatial rate of late-time gravitational-potential decay. The ISW signal amplitude follows from convolving that uniform decay rate with the foreground matter distribution. A persistent low amplitude demands lower σ₈ (worsening S₈ tension), modified gravity, or unaccounted survey systematics.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, the rate of gravitational-potential decay becomes environment-dependent. Λ_eff(x,t) is locally enhanced inside voids and locally suppressed inside clusters (P17, P19); potentials in voids decay faster while potentials in overdense regions decay more slowly. The integrated ISW signal averages over this spatial variability rather than expressing a single uniform decay rate.
Spatial averaging of a non-uniform field naturally produces a lower mean amplitude than the constant-field prediction would deliver. Some sightlines pass mostly through voids and pick up a strong ISW signal; some pass mostly through overdensities and pick up a weak signal; the cross-correlation with the LSS distribution weights these contributions in a way that does not perfectly align with the ΛCDM template. The result is the observed lower-than-predicted ISW amplitude with inter-survey scatter that reflects which regions of the Λ_eff landscape each survey sampled.
The Granett supervoid-stacking anomaly (where the void-stacking ISW signal exceeds the ΛCDM prediction) is the predicted natural outcome of M5: void regions carry the strongest local Λ_eff enhancement and therefore the strongest deviation from the global average. Gravitational superposition (P50, P52) adds the Φ_mesh contribution that modifies the cluster-side ISW signal as well. The same M5 mechanism that resolves the Hubble tension, S₈ deficit, evolving-w(z), and angular-diameter-distance shape produces the ISW deficit naturally. There is no need to invoke new dark-sector physics.
If a precision Euclid + LSST + CMB-S4 ISW × LSS cross-correlation reaches the full ΛCDM-predicted amplitude with no inter-survey scatter and no void-direction enhancement of the deviation, the M5 dynamical-Λ_eff explanation is refuted. The cross-correlation amplitude in void-dominated sightlines should be enhanced relative to cluster-dominated sightlines after standard kinematic corrections.