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Persistent and serious challenge to the $Λ$CDM throne: Evidence for dynamical dark energy rising from combinations of different types of datasets

Mustapha Ishak, Leonel Medina-Varela

TL;DR

This work tests whether dark energy evolves with time by contrasting a time-varying EOS model $w_0w_a$CDM against the constant-$w$ cosmological constant $Λ$CDM using diverse datasets (BAO from DESI/DES, CMB with/without lensing from Planck and ACT, SN, and DES3x2pts). The authors perform a robustness check by excluding one data type at a time and then combine all data types, employing a CPL parametrization $w(z)=w_0+w_a\frac{z}{1+z}=w_0+w_a(1-a)$ and Bayesian model comparison via $\Delta\chi^2_{MAP}$ and $\Delta(DIC)$. Across all exclusion tests, the data favor dynamical dark energy with $w_0>-1$ and $w_a<0$, at significances up to ~$3.3\sigma$, and the full data combinations reach about $4\sigma$ in some cases (e.g., $\text{DESI}+\text{DESY6BAO}+\text{CMBL}+\text{DESY5SN}$). Taken together, these results present a compelling, though prudent, challenge to the $Λ$CDM throne, suggesting either new physics in a dynamical dark energy sector or modifications to gravity, while underscoring the need for further data and careful control of systematics.

Abstract

We derive multiple constraints on dark energy and compare dynamical dark energy models with a time-varying equation of state ($w_0 w_a$CDM) versus a cosmological constant model ($Λ$CDM). We use Baryon Acoustic Oscillation (BAO) from DESI and DES, Cosmic Microwave Background from Planck with and without lensing from Planck and ACT (noted CMBL and CMB, respectively), supernova (SN), and cross-correlations between galaxy positions and galaxy lensing from DES. First, we use pairs or trios of datasets where we exclude one type of dataset each time and categorize them as ``NO SN", ``NO CMB" and ``NO BAO" combinations. In all cases, we find that the combinations favor the $w_0 w_a$CDM model over $Λ$CDM, with significance ranging from 2.3$σ$ to 3.3$σ$. For example, DESI+DESY6BAO+CMB yields 3.2$σ$ without SN, DESI+DESY6BAO+DESY5SN yields 3.3$σ$ without CMB, and CMB+DESY5SN+DES3x2pts yields 2.6$σ$ without BAO. The persistence of this pattern across various dataset combinations even when any of the datasets is excluded supports an overall validation of this trending result regardless of any specific dataset. Next, we use larger combinations of these datasets after verifying their mutual consistency within the $w_0 w_a$CDM model. We find combinations that give significance levels $\sim$4$σ$, with DESI+DESY6BAO+CMBL+DESY5SN reaching 4.4$σ$. In sum, while we need to remain prudent, the combination of the first step that supports a validation of the pattern of these results beyond any single type of dataset and their associated systematics, together with the second step showing high-significance results when such datasets are combined, presents a compelling overall portrait in favor of a dynamical dark energy with a time-evolving equation of state over a cosmological constant, and constitutes a serious challenge to the $Λ$CDM model's reign. Abridged.

Persistent and serious challenge to the $Λ$CDM throne: Evidence for dynamical dark energy rising from combinations of different types of datasets

TL;DR

This work tests whether dark energy evolves with time by contrasting a time-varying EOS model CDM against the constant- cosmological constant CDM using diverse datasets (BAO from DESI/DES, CMB with/without lensing from Planck and ACT, SN, and DES3x2pts). The authors perform a robustness check by excluding one data type at a time and then combine all data types, employing a CPL parametrization and Bayesian model comparison via and . Across all exclusion tests, the data favor dynamical dark energy with and , at significances up to ~, and the full data combinations reach about in some cases (e.g., ). Taken together, these results present a compelling, though prudent, challenge to the CDM throne, suggesting either new physics in a dynamical dark energy sector or modifications to gravity, while underscoring the need for further data and careful control of systematics.

Abstract

We derive multiple constraints on dark energy and compare dynamical dark energy models with a time-varying equation of state (CDM) versus a cosmological constant model (CDM). We use Baryon Acoustic Oscillation (BAO) from DESI and DES, Cosmic Microwave Background from Planck with and without lensing from Planck and ACT (noted CMBL and CMB, respectively), supernova (SN), and cross-correlations between galaxy positions and galaxy lensing from DES. First, we use pairs or trios of datasets where we exclude one type of dataset each time and categorize them as ``NO SN", ``NO CMB" and ``NO BAO" combinations. In all cases, we find that the combinations favor the CDM model over CDM, with significance ranging from 2.3 to 3.3. For example, DESI+DESY6BAO+CMB yields 3.2 without SN, DESI+DESY6BAO+DESY5SN yields 3.3 without CMB, and CMB+DESY5SN+DES3x2pts yields 2.6 without BAO. The persistence of this pattern across various dataset combinations even when any of the datasets is excluded supports an overall validation of this trending result regardless of any specific dataset. Next, we use larger combinations of these datasets after verifying their mutual consistency within the CDM model. We find combinations that give significance levels 4, with DESI+DESY6BAO+CMBL+DESY5SN reaching 4.4. In sum, while we need to remain prudent, the combination of the first step that supports a validation of the pattern of these results beyond any single type of dataset and their associated systematics, together with the second step showing high-significance results when such datasets are combined, presents a compelling overall portrait in favor of a dynamical dark energy with a time-evolving equation of state over a cosmological constant, and constitutes a serious challenge to the CDM model's reign. Abridged.

Paper Structure

This paper contains 11 sections, 3 equations, 6 figures, 5 tables.

Table of Contents

  1. Introduction
  2. methodology and data
  3. Background and formalism
  4. Datasets
  5. Validation by exclusion
  6. NO SN Data
  7. NO CMB Data
  8. NO BAO Data
  9. Putting it all together
  10. Conclusion
  11. Parameters and priors

Figures (6)

  • Figure 1: No-SN dataset combination plots: 68% and 95% marginalised posterior constraints in the $w_0$--$w_a$ plane for the flat $w_0w_a$CDM model. Each of these combinations favors the quadrant $w_0>-1$, $w_a<0$, and exhibits a preference of time-evolving EOS dynamical dark energy over a cosmological constant. The corresponding constraints and significance details are provided in \ref{['tab:no_SN']}.
  • Figure 2: No-CMB dataset combination plots: 68% and 95% marginalised posterior constraints in the $w_0$--$w_a$ plane for the flat $w_0w_a$CDM model. Each of the combinations primarily favors the quadrant $w_0>-1$, $w_a<0$, and exhibits a preference of dynamical dark energy with a time-evolving equation of state over a cosmological constant. The corresponding constraints and significance details are provided in \ref{['tab:no_CMB']}.
  • Figure 3: No-BAO dataset combination plots: 68% and 95% marginalised posterior constraints in the $w_0$--$w_a$ plane for the flat $w_0w_a$CDM model. Each of these combinations majoritarily favors the quadrant $w_0>-1$, $w_a<0$, and exhibits a preference of time-evolving EOS dynamical dark energy over a cosmological constant. The corresponding constraints and significance details are provided in \ref{['tab:no_BAO']}.
  • Figure 4: Larger combinations of dataset result plots: 68% and 95% marginalised posterior constraints in the $w_0$--$w_a$ plane for the flat $w_0w_a$CDM model. Each of these combinations favors the quadrant $w_0>-1$, $w_a<0$, and exhibits a preference of time-evolving EOS dynamical dark energy over a cosmological constant. The corresponding constraints and significance details are provided in \ref{['tab:HS_comb']}.
  • Figure 5: Summary plot of the 1-D constraints on the equations of state parameters from the dataset combinations used providing the marginalized means and 68% credible intervals on $w_0$ (top panel) and $w_a$ (bottom panel). Data combinations organized in NO SN, NO CMB, NO BAO and then all 3 types combined. The vertical black dashed lines represent the $w_0=-1.0$ and $w_a=0.0$ of the cosmological constant. Each combination in the 6 pairs (or trios) at the top of each panel show a preference for the data combination of the $w_0w_a$CDM model over the $\Lambda$CDM model regardless of the type of data excluded. Below that, the combinations of the three types of data provide tighter constraints with higher significance for such a preference pattern as given in \ref{['tab:HS_comb']}. The two panels show an overall persistent portrait that is not in favor of the standard $\Lambda$CDM model.
  • ...and 1 more figures