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

Shibendu Gupta Choudhury, Anjan A Sen

Abstract

Recent cosmological observations show hints for possible deviations from the standard $Λ$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 $Λ$CDM and remains competitive with standard dynamical dark energy models. The inferred expansion history exhibits noticeable deviations from $Λ$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.

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

Abstract

Recent cosmological observations show hints for possible deviations from the standard 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, , follows a logistic evolution motivated by a renormalization group like flow between cosmological fixed points. This approach directly reconstructs 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 CDM and remains competitive with standard dynamical dark energy models. The inferred expansion history exhibits noticeable deviations from 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.
Paper Structure (7 sections, 16 equations, 5 figures, 4 tables)

This paper contains 7 sections, 16 equations, 5 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Theoretical Framework: Logistic RG Flow Evolution of the Cosmic Equation of State
  3. Datasets and Methodology
  4. Results
  5. Conclusions
  6. Evolution of $w_{\rm{T}}$ and $\frac{\rm{d}w_{\rm{T}}}{\rm{d}z}$
  7. A possible underlying model with an extra dark component

Figures (5)

  • Figure 1: One-dimensional marginalized posterior distributions, 2 dimensional contour plots at 68% and 95% C.L. limits for the parameters of the Logistic model using different dataset combinations.
  • Figure 2: Evolution of the expansion history $H(z)/(1+z)$ (left panel) and the total equation of state $w_{\rm T}(z)$ (right panel) for the Logistic, $\Lambda$CDM, and CPL models using the constraints obtained from the DESI-DR2 + DES + CMB dataset combination.
  • Figure 3: Evolution of the jerk parameter $j(z)$ for the Logistic, $\Lambda$CDM, and CPL models using the DESI-DR2 + DES + CMB constraints (left panel). The right panel shows the reconstructed $j(z)$ for the Logistic model obtained from different dataset combinations.
  • Figure 4: Evolution of $w_{\rm T}$ (upper panel) and $\frac{{\rm d}w_{\rm T}}{{\rm d}z}$ (lower panel) extrapolated to future for the models considered.
  • Figure 5: Comparison of $w_\text{T}$ for the Logistic model and a model with an additional $X$-fluid.