Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Is CPL dark energy a mirage?

Mikel Artola, Ismael Ayuso, Ruth Lazkoz, Vincenzo Salzano

TL;DR

The paper assesses whether the CPL dark energy parameterization is a mirage by proposing two sigmoid-based two-parameter extensions that mimic CPL locally but soften early-time phantom behavior. Using DESI BAO, Pantheon+ SNeIa, and compressed CMB shift parameters, the authors perform MCMC and Bayesian model comparison, finding that the CPL form remains statistically competitive and that the alternatives are not decisively favored or ruled out. They show that current data partially constrain the late-time evolution of w(a) but are insufficient to sharply distinguish CPL from smooth sigmoid deformations, especially as n grows and the models converge to CPL. The work highlights the robustness of CPL within the probed redshift range and outlines how non-linear, high-redshift DE dynamics could still be explored with future precision data.

Abstract

Recent observations from the Dark Energy Spectroscopic Instrument (DESI) raise doubts about the standard cosmological model, $Λ$CDM, suggesting a preference for an inherently dynamical dark energy component. The Chevallier-Polarski-Linder (CPL) parameterization -- a widely used two-parameter model for the dark energy equation of state -- displays marked early-time phantom behavior and a recent crossing of the phantom divide. These features suggest the convenience to check observationally the robustness of such evolution. To address this, we design two alternative families of two-parameter dark energy parameterizations which remain close to the original CPL but aim to soften its phantom character. Specifically, these models reproduce CPL-like behavior at low redshift but mitigate early phantom behavior through the use of smooth sigmoid transitions, yielding a more gradual evolution. By combining recent DESI data with constraints from the cosmic microwave background and Type Ia supernovae, we assess the viability of these models. Our analysis shows that CPL remains a strong and competitive parameterization, with the proposed alternatives only marginally favored or disfavored. We conclude that current observational data lack the statistical precision to decisively distinguish between CPL and similarly constructed parameterizations across the redshift range probed by late-time observables.

Is CPL dark energy a mirage?

TL;DR

The paper assesses whether the CPL dark energy parameterization is a mirage by proposing two sigmoid-based two-parameter extensions that mimic CPL locally but soften early-time phantom behavior. Using DESI BAO, Pantheon+ SNeIa, and compressed CMB shift parameters, the authors perform MCMC and Bayesian model comparison, finding that the CPL form remains statistically competitive and that the alternatives are not decisively favored or ruled out. They show that current data partially constrain the late-time evolution of w(a) but are insufficient to sharply distinguish CPL from smooth sigmoid deformations, especially as n grows and the models converge to CPL. The work highlights the robustness of CPL within the probed redshift range and outlines how non-linear, high-redshift DE dynamics could still be explored with future precision data.

Abstract

Recent observations from the Dark Energy Spectroscopic Instrument (DESI) raise doubts about the standard cosmological model, CDM, suggesting a preference for an inherently dynamical dark energy component. The Chevallier-Polarski-Linder (CPL) parameterization -- a widely used two-parameter model for the dark energy equation of state -- displays marked early-time phantom behavior and a recent crossing of the phantom divide. These features suggest the convenience to check observationally the robustness of such evolution. To address this, we design two alternative families of two-parameter dark energy parameterizations which remain close to the original CPL but aim to soften its phantom character. Specifically, these models reproduce CPL-like behavior at low redshift but mitigate early phantom behavior through the use of smooth sigmoid transitions, yielding a more gradual evolution. By combining recent DESI data with constraints from the cosmic microwave background and Type Ia supernovae, we assess the viability of these models. Our analysis shows that CPL remains a strong and competitive parameterization, with the proposed alternatives only marginally favored or disfavored. We conclude that current observational data lack the statistical precision to decisively distinguish between CPL and similarly constructed parameterizations across the redshift range probed by late-time observables.

Paper Structure

This paper contains 14 sections, 31 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Why and how to specify w(a)
  3. Data and methodology
  4. datasets
  5. Baryon acoustic oscillations
  6. Type Ia supernovae
  7. Cosmic microwave background
  8. Method and model comparison
  9. Results and discussion
  10. Evidence in favor of dynamical dark energy
  11. Performance of the sigmoid families
  12. Equation of state parameters
  13. Matter, baryons and Hubble parameter
  14. Summary and conclusions

Figures (4)

  • Figure 1: Relative difference between the EoS for the proposed families of parameterizations and CPL, defined as $(w_i - w_\mathrm{CPL})/\vert w_\mathrm{CPL} \vert$, for the CBS data combination. Positive values in the vertical axis denote a reduced phantom effect in comparison to CPL. The dashed line corresponds to values of the EoS that coincide with CPL.
  • Figure 2: $68\%$ and $95\%$ confidence-level regions of the CPL parameterization in the $(w_0, w_a)$ for various survey combinations. Negligible shifts are anticipated for the Sqrt$n$ and $n$Tanh parameterizations and we opt for not illustrating these; see the $(w_0, w_a)$ panel in the corner plot of Fig. \ref{['fig:triangle_FULL']}.
  • Figure 3: $w(a)$ for the best fit values of $(w_0,w_a)$ (CBS data combination) across the cosmological history for CPL, Sqrt and Tanh. Sqrt$n$ and $n$Tanh are the parameterizations that show the most significant deviation from CPL.
  • Figure 4: Marginalized posterior distributions of $(\Omega_\mathrm{m}, \Omega_\mathrm{b}, H_0, w_0, w_a)$ derived from the CMB$+$BAO$+$SNeIa combination for the CPL parameterization, along with two exemplars each from the Sqrt$n$ and $n$Tanh families. The $\Lambda$CDM value of the EoS is included in the $(w_0, w_a)$ plane as a reference.