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

TL;DR

This paper introduces a logistic flow model for the Universe's equation of state to explore deviations from the standard cosmological model, fitting observational data better and revealing low-redshift dynamics.

Contribution

It proposes a novel logistic RG-like flow framework for $w_T(z)$ that does not assume a specific dark energy model, fitting data effectively and offering a new perspective on cosmic evolution.

Findings

Logistic parametrization improves fit over $ ext{Lambda}$CDM.

Reconstructed expansion history shows deviations at low redshift.

Flow-inspired models are promising for late-time cosmology analysis.

Abstract

Recent cosmological observations show hints for possible deviations from the standard $\Lambda$CDM paradigm at late times. To study such deviation, we introduce a minimal phenomenological framework in which the total equation of state of the Universe, $w_{\rm T}(z)$, follows a logistic evolution motivated by a renormalization group like flow between cosmological fixed points. This approach directly reconstructs $w_{\rm T}(z)$ probed by background observables, without assuming a specific dark energy model. Using DESI-DR2 baryon acoustic oscillation measurements, DES-Dovekie latest supernova data, and CMB distance priors, we find that the logistic parametrization provides an improved fit compared to $\Lambda$CDM and remains competitive with standard dynamical dark energy models. The inferred expansion history exhibits noticeable deviations from $\Lambda$CDM at low redshifts, reflected in the reconstructed jerk parameter. While the statistical significance of these deviations is model-dependent, our results highlight the potential of flow-inspired parametrizations as a complementary and physically interpretable framework for probing late-time cosmic dynamics.