Low-Frequency Plateaus and the ISW Anomaly as Observational Signatures of Retentional Cosmology

This paper proposes two directly testable observational criteria distinguishing retentional cosmology from the standard ΛCDM model: (i) the emergence of a low-frequency power plateau in relic background spectra and (ii) suppression of the late-time Integrated Sachs–Wolfe (ISW) effect at large angular scales (ℓ ≲ 20). A minimal retentional modification of late-time cosmological dynamics is introduced via a saturating response Λψ, which leads to a finite correlation horizon and a stationary asymptotic regime instead of de Sitter acceleration. Analytical conditions for the existence of a spectral floor are derived, together with explicit deformation of the ISW transfer function. Conservative parameter bounds for detectability are specified, and a strict joint falsification criterion is formulated: the theory is discarded unless both signatures are simultaneously observed. The work provides a clear observational framework for testing whether cosmic persistence is driven by accelerated expansion or by structural retention. The analysis does not replace ΛCDM in its established regimes but isolates a boundary domain where standard cosmological assumptions structurally fail and retentional physics becomes testable.