Beyond $\Lambda$CDM with a Logistic RG-like Flow of the Low Redshift Cosmic Evolution

Abstract

Recent observations hint at possible late-time deviations from $\Lambda$CDM. We introduce a minimal phenomenological framework in which the total equation of state $w_{\mathrm{T}}(z)$ follows a logistic evolution motivated by renormalization-group-like flow between cosmological fixed points. Using DESI-DR2 BAO, DES supernova data, and CMB distance priors, we find that this parametrization provides an improved description of the expansion history relative to $\Lambda$CDM. The reconstructed evolution, though model specific, also shows statistically strong low-redshift deviations from $\Lambda$CDM.

8 pages, 4 figures, version accepted for publication in PRD