Dynamical Dark Energy in the Crosshairs: A Joint Analysis with DESI, Pantheon plus, and TDCOSMO Constraints

TL;DR

The paper addresses whether dark energy evolves over cosmic time by performing a joint analysis of three representative models—ΛCDM, the CPL parametrization, and the GEDE model—using DESI DR1/DR2 BAO, Pantheon Plus SNe Ia, and TDCOSMO time-delay lensing data. The multi-probe combination breaks key degeneracies among $H_0$, $r_d$, and $M_B$, yielding tight constraints on the dark-energy parameters: CPL yields $w_0\approx-0.87$ and $w_a\approx-0.41$ to $-0.53$, while GEDE constrains the transition parameter $\Delta$ to about $-0.50$ to $-0.52$ with a derived transition redshift $z_t\approx0.36$, both indicating quintessence-like behavior and evolution away from a cosmological constant. The joint data provide modest improvements over ΛCDM with $\Delta\chi^2$ reductions around $-3.6$ to $-4.2$ for the combined datasets, and the GEDE $\Delta$ is detected at $\sim 2.4$–$2.9\sigma$, challenging the pure ΛCDM picture and disfavoring the Δ=1 PEDE scenario by over $3\sigma$. Overall, the results support a phenomenologically viable dynamical dark energy component and illustrate the power of combining BAO, SNe Ia, and time-delay lensing to probe dark energy evolution, while highlighting the need for future data to decisively distinguish between competing dynamical models.

Abstract

In this work, we perform a comprehensive joint analysis of three representative dark energy models - ${\rmΛCDM}$, the Chevallier-Polarski-Linder (CPL) parametrization, and the Generalised Emergent Dark Energy (GEDE) model - using the latest observational datasets: baryon acoustic oscillation (BAO) measurements from DESI Data Releases 1 and 2 (DR1/DR2), the Pantheon Plus sample of Type Ia supernovae (SNe Ia), and time-delay cosmography from TDCOSMO lensing. The CPL model yields a statistically significant improvement over ${\rmΛCDM}$, with $Δχ^2 = -3.6$ for DESI DR2+Pantheon Plus+TDCOSMO, favoring a quintessence-like behavior ($w_0=-0.87^{+0.05 }_{-0.05} $, $w_a=-0.41^{+ 0.28}_{-0.28}$ at 1$σ$ confidence level). The GEDE model also exhibits slightly favoring than ${\rmΛCDM}$ with observations, yielding $Δχ^2 =-2.83$ (DR1) and $Δχ^2 = -3.82$ (DR2). The captured potential dark energy evolution transition parameter $Δ$ in GEDE model is constrained to $-0.52^{+0.22}_{-0.20}$ (DR1) and $-0.50^{+0.18}_{-0.17}$ (DR2), showing a $2.4σ$ and $2.9σ$ deviation from zero respectively. This statistically significant ($>2σ$) non-zero value of $Δ$ provides evidence against a pure cosmological constant scenario. The negative sign indicates quintessence-like behavior ($w > -1$) in the late universe. Notably, the GEDE constraints show a $>3σ$ tension with the $Δ=1$ (Phenomenological Emergent Dark Energy model) predictions. This significant discrepancy implies that while both models belong to the emergent dark energy family, their fundamentally different transition mechanisms lead to distinct cosmological implications. Our results collectively suggest that GEDE provides a phenomenologically viable alternative to $Λ$CDM.

Figures (4)

• Figure 1: The one and two-dimensional marginalised posterior distributions of $H_0$, $\Omega_m$, $r_d$, $M_B$ in a $\rm{\Lambda}CDM$ cosmology from the DESI DR1/DR2+Pantheon Plus+TDCOSMO lenes datasets (the green regions derived from DESI DR1 dataset, the yellow regions derived from DESI DR2 dataset). The gray dashed line is the best-fitting value of $H_0=67.4$$\mathrm{~km~s^{-1}~Mpc^{-1}}$ from Planck CMB results.
• Figure 2: The one and two-dimensional marginalised posterior distributions of $H_0$, $\Omega_m$, $\Delta$, $r_d$, $M_B$ in a GEDE cosmology.
• Figure 3: The one and two-dimensional marginalised posterior distributions of $H_0$, $\Omega_m$, $w_0$, $w_a$, $r_d$, $M_B$ in a CPL cosmology from the DESI DR1/DR2+Pantheon Plus+TDCOSMO lenses datasets (the green regions derived from DESI DR1 dataset, the yellow regions derived from DESI DR2 dataset). The gray dashed line is the best-fitting value of $H_0=67.4$$\mathrm{~km~s^{-1}~Mpc^{-1}}$ from Planck CMB results.
• Figure 4: The equation of state of dark energy with $\rm{\Lambda}CDM$, GEDE, and CPL models using DESI DR2, Pantheon Plus SNe Ia, and TDCOSMO lensing datasets. The dashed green line shows the best-fitting $w(z)$ based on $w_0$ and $w_a$ inference and the green regions around it represent the 68% and 95% confdence intervals. The dashed blue line represents the $\rm{\Lambda}CDM$ model, and the dashed orange line represents GEDE model.