ΛCDM-E: Entropy as a Possible Dark Energy Component within the ΛCDM Framework

Abstract This document presents the current version (v3.1) of the ΛCDM-E (Lambda-CDM Entropy) framework — an ongoing research program exploring whether part of the observed dark-energy behaviour can be physically attributed to entropy work at the cosmic horizon. The study extends the standard ΛCDM cosmological model by introducing an entropy coupling term (γ·ln(a)) derived from thermodynamic first principles. Across five progressive research phases using calibrated H(z) and SNe Ia datasets, the framework achieved a strong statistical indication (8.9σ) for a nonzero entropy parameter γ = 0.6289 ± 0.047, corresponding to a 77.6% Akaike weight over standard ΛCDM. Unlike a new energy source, this term represents entropy work capacity — the reversible component of cosmic expansion energy linked to horizon thermodynamics. When normalized to the dark-energy sector, this corresponds to roughly 45.6% of the total dark-energy effect, suggesting that entropy may play a substantial but not dominant role in the observed cosmic acceleration. This refinement replaces an earlier exploratory upper estimate of ~63%, aligning more closely with physically realistic expectations. ΛCDM-E retains full consistency with current observations while offering testable predictions for modest deviations (4–8%) in the Hubble parameter at intermediate redshifts (0.5 ≤ z ≤ 2.0), small distance-modulus offsets (Δμ ≈ 0.01–0.03 mag), mild suppression in structure growth (2–3%), and an enhanced late Integrated Sachs–Wolfe signal. These effects can be verified or falsified by DESI, Euclid, and other upcoming cosmological surveys. This is an independent, ongoing research effort, not yet peer reviewed, and future versions will continue refining the model, datasets, and interpretations. Collaboration, replication, and critique are openly invited. Interested researchers may contact the author at [email protected] to contribute to this continuing investigation into entropy and dark energy.