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Empirical Validation: Investigating the $Λ_s $CDM Model with new DESI BAO Observations

Manish Yadav, Archana Dixit, Anirudh Pradhan, M S Barak

TL;DR

The paper tests a minimal Λ$_s$CDM extension with a sign-switching cosmological constant, introducing a transition redshift $z_\dagger$ to alleviate the Hubble tension and $S_8$ discrepancy. Using Planck 2018, Pantheon, and DESI BAO data, it shows that $z_\dagger$ remains unconstrained with Planck alone but becomes progressively constrained when DESI BAO and SN data are included, with Bayesian evidence varying by dataset. The results indicate that Λ$_s$CDM can raise $H_0$ values toward local measurements and reduce $S_8$ tensions, though a decisive preference over ΛCDM is dataset-dependent; DR2+PP&SH0ES favors $z_\dagger \approx 1.39$ and $H_0 \approx 73$ km s$^{-1}$ Mpc$^{-1}$, aligning with SH0ES. Overall, the sign-switching dark energy framework remains a viable, mildly preferred model that could reshape our understanding of late-time cosmic acceleration, warranting further investigation with forthcoming high-precision data.

Abstract

The $Λ$CDM model has long served as the cornerstone of modern cosmology, offering an elegant and successful framework for interpreting a wide range of cosmological observations. However, the rise of high-precision datasets has revealed statistically significant tensions, most notably the Hubble tension and the $S_8$ discrepancy, which challenge the completeness of this standard model. In this context, we explore the $Λ_{\rm s}$CDM model-an extension of $Λ$CDM featuring a single additional parameter, $z_\dagger$, corresponding to a sign-switching cosmological constant. This minimal modification aims to alleviate key observational tensions without compromising the model's overall coherence. Recent findings present in the literature indicate that the $Λ_{\rm s}$CDM model not only provides a better fit to Lyman-$α$ forest data for $z_\dagger < 2.3$, but also accommodates both the SH0ES measurement of $H_0$ and the angular diameter distance to the last scattering surface when 2D BAO data are included. We present a comprehensive analysis combining the full Planck 2018 CMB data, the Pantheon Type Ia Supernovae sample, and the recently released Baryon Acoustic Oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI). Our finding reveal that the Preliminary DESI results, a possible $3.9σ$ deviation from $Λ$CDM expectations, reinforce the importance of exploring such dynamic dark energy frameworks. In sum, our study underscores the potential of $Λ_{\rm s}$CDM to reconcile multiple cosmological tensions and sheds light on the role of upcoming high-precision observations in reshaping our understanding of the universe's expansion history and the nature of dark energy.

Empirical Validation: Investigating the $Λ_s $CDM Model with new DESI BAO Observations

TL;DR

The paper tests a minimal ΛCDM extension with a sign-switching cosmological constant, introducing a transition redshift to alleviate the Hubble tension and discrepancy. Using Planck 2018, Pantheon, and DESI BAO data, it shows that remains unconstrained with Planck alone but becomes progressively constrained when DESI BAO and SN data are included, with Bayesian evidence varying by dataset. The results indicate that ΛCDM can raise values toward local measurements and reduce tensions, though a decisive preference over ΛCDM is dataset-dependent; DR2+PP&SH0ES favors and km s Mpc, aligning with SH0ES. Overall, the sign-switching dark energy framework remains a viable, mildly preferred model that could reshape our understanding of late-time cosmic acceleration, warranting further investigation with forthcoming high-precision data.

Abstract

The CDM model has long served as the cornerstone of modern cosmology, offering an elegant and successful framework for interpreting a wide range of cosmological observations. However, the rise of high-precision datasets has revealed statistically significant tensions, most notably the Hubble tension and the discrepancy, which challenge the completeness of this standard model. In this context, we explore the CDM model-an extension of CDM featuring a single additional parameter, , corresponding to a sign-switching cosmological constant. This minimal modification aims to alleviate key observational tensions without compromising the model's overall coherence. Recent findings present in the literature indicate that the CDM model not only provides a better fit to Lyman- forest data for , but also accommodates both the SH0ES measurement of and the angular diameter distance to the last scattering surface when 2D BAO data are included. We present a comprehensive analysis combining the full Planck 2018 CMB data, the Pantheon Type Ia Supernovae sample, and the recently released Baryon Acoustic Oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI). Our finding reveal that the Preliminary DESI results, a possible deviation from CDM expectations, reinforce the importance of exploring such dynamic dark energy frameworks. In sum, our study underscores the potential of CDM to reconcile multiple cosmological tensions and sheds light on the role of upcoming high-precision observations in reshaping our understanding of the universe's expansion history and the nature of dark energy.

Paper Structure

This paper contains 5 sections, 3 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. MODEL, DATASETS AND METHODOLOGY
  3. Results and discussion
  4. Comparative Analysis of DESI BAO and DR2 Datasets
  5. Conclusion

Figures (8)

  • Figure 1: Marginalized one- and two-dimensional distributions (68$\%$ and 95$\%$ CLs) of the $\Lambda_s$CDM model parameters for different datasets combinations: Pk18, Pk18+ DESI BAO, and Pk18+ DESI BAO+PP$\&$SH0ES.
  • Figure 2: Marginalized one- and two-dimensional distributions (68% and 95% CLs) of the $\Lambda$CDM model parameters for different datasets combinations: Pk18, Pk18+ DESI BAO, and Pk18+ DESI BAO+PP&SH0ES.
  • Figure 3: The left side 2D contour plots in the $H_0$-$\Omega_{\rm m}$ plane, and the right side 2D contour plots in the $S_8$-$\Omega_{\rm m}$ plane, and the middle bottem 2D contour plots in the $sigma_8$-$10^2\omega_{\rm b}$ plane shown at 68$\%$ and 95$\%$ CL for the $\Lambda_{\rm s}$CDM and $\Lambda$CDM models with Pk18, Pk18+DESI BAO, and Pk18+DESI BAO+PP$\&$SH0ES.
  • Figure 4: The left side 2D contour plots in the $z_{\dagger}$-$H_0$ plane, and the right side 2D contour plots in the $z_{\dagger}$-$\Omega_{\Lambda_{\rm s}}$ plane,shown at 68$\%$ and 95$\%$ CL for the $\Lambda_{\rm s}$CDM model with Pk18, Pk18+DESI BAO, and Pk18+DESI BAO+PP$\&$SH0ES.
  • Figure 5: Statistical reconstruction of the rescaled expansion rate of the universe, $H(z)/(1 + z)$, at $1\sigma$ for the $\Lambda$CDM and $\Lambda_s$CDM models, based on the joint analysis of Pk18+DESI BAO, and Pk18+DESI BAO+PP$\&$SH0ES.
  • ...and 3 more figures