Compton y-distortions measured by Planck imply lower σ₈ or less hot-ICM thermal energy than ΛCDM predicts from CMB anisotropies (Hill 2014; Planck 2016). The y-distortion deficit tracks the same suppressed late-clustering signal as the S₈ tension, with FIRAS bounding |y| < 1.5 × 10⁻⁵. The model has no clean physical handle that would suppress y-amplitude without disturbing other constraints.
The standard model assumes smooth structure growth tied to CMB initial conditions through a constant Λ. Late-time hot-ICM amplitude must therefore match Planck-extrapolated predictions. A persistent y-distortion deficit has nowhere to go in the model except as missing feedback physics or as a systematic in cluster-scale baryon accounting.
SCT replaces the hot-dense-center with a superluminal collision and the thermalized debris field. From this single change, Λ becomes the dynamical ratio Λ_eff(x,t) = κ · U_local(x,t) / U_parent(x,t) (P17). The Λ_eff field is locally enhanced inside our KBC supervoid (P19), suppressing local structure-growth amplitude and therefore the hot-ICM thermal energy that sources the integrated y-distortion (P14, P15, P16).
The y-distortion deficit is the same physical phenomenon as the S₈ tension and the σ₈(z) growth kink (recid 15), measured on a different observable. CMB photons traversing the late universe pick up Compton scattering from hot electrons in clusters; if cluster amplitudes are systematically lower than ΛCDM expects (because local Λ_eff is suppressing growth in our void-dominated volume), the integrated y signal comes in low. FIRAS bounds the cumulative cascade-epoch energy injection at |y| < 1.5 × 10⁻⁵, which the cascade-termination constraint (P40, ending well before t ≈ 1 second) easily satisfies. The cascade-epoch contribution to y is roughly 2 × 10⁻⁶, four orders below the FIRAS bound.
The same M5 mechanism resolves the Hubble tension, the S₈ deficit, the σ₈(z) growth kink, the cluster L_X-T relation steepening, and the ICM entropy floor. The y-distortion deficit is one more observational window onto the locally suppressed late-time clustering that follows from environmental Λ_eff variability. There is no need to invoke missing baryonic feedback channels, AGN-feedback fine-tuning, or modified gravity.
If high-redshift y-distortion stacking (PIXIE, future spectral-distortion missions) measures the cumulative integrated y consistent with full ΛCDM amplitude (showing zero suppression in cluster amplitudes outside our local KBC region), the M5 environmental explanation fails. Specifically, void-direction stacking should yield lower y per cluster than overdensity-direction stacking at greater than 2σ.