Reconstruction of dark energy using DESI DR2

TL;DR

This work tests the nature of dark energy by reconstructing the expansion history in a model-independent way using Gaussian processes. By deriving $E(z)$, $q(z)$, and $w(z)$ from the dimensionless luminosity distance $D(z)$ and its derivatives, the authors compare against $Λ$CDM through multiple data sets: PantheonPlus+SH0ES, GRB, observational $H(z)$, and DESI DR2 BAO. They find $E(z)$ is consistent with $Λ$CDM at $z<2$, while $q(z)$ shows deviations at $z<0.3$, and $w(z)$ exhibits evolution with a transition around $z_{wt}≈0.46$, suggesting possible dynamic dark energy. Adding GRB, OHD, and DESI DR2 BAO data improves constraints, particularly on high-redshift behavior and derivative information, underscoring the value and limits of nonparametric reconstruction for probing dark energy.

Abstract

Using a model-independent Gaussian process (GP) method to reconstruct the dimensionless luminosity distance $D$ and its derivatives, we derive the evolution of the dimensionless Hubble parameter $E$, the deceleration parameter $q$, and the state parameter $w$ of dark energy. We utilize the PantheonPlus, SH0ES, and Gamma Ray Burst (GRB) data to derive the dimensionless luminosity distance $D$. Additionally, we employ observational $H(z)$ data (OHD) and baryon acoustic oscillations (BAO) from Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) to obtain the first derivative of the dimensionless luminosity distance $D^{'}$. To obtain the reconstructed $D$ and $D^{'}$, we utilize the fiducial value from each dataset, with particular emphasis on the varying $H_0$. According to the reconstruction results obtained from PantheonPlus+SH0ES+GRB+OHD and PantheonPlus+SH0ES+GRB+OHD+DESI data, we find that $E$ are consistent with the predictions of the $Λ$CDM model at a $2σ$ confidence level within the redshift range of $z<2$. However, the reconstruction results for $q$ exhibit deviations from the $Λ$CDM model in the range of $z<0.3$. Furthermore, we observe that the mean value of $w$ exhibits evolving behavior, transiting from $w < -1$ to $w > -1$ around $z_{\rm wt}=0.464^{+0.235}_{-0.120}$. Combining data from DESI DR2 can slightly enhance the accuracy of our constraints.

Figures (2)

• Figure 1: The reconstruction of $D$ along with its first and second derivatives. It is organized into four rows, corresponding to four different joint datasets: PantheonPlus+SH0ES, PantheonPlus+SH0ES+GRB, PantheonPlus+SH0ES+GRB+OHD, and PantheonPlus+SH0ES+GRB+OHD+DESI. The black dashed line represents the theoretical curve of the $\Lambda$CDM model. The shaded areas in dark grey and light grey are the confidence intervals of 1$\sigma$ and 2$\sigma$, respectively. Additionally, the mean values and error bars, depicted in light blue, dark blue, red and orange, correspond to the PantheonPlus+SH0ES, GRB, OHD and DESI datasets, respectively.
• Figure 2: Reconstruction of the evolution of $E$, $q$, and $w$ utilizing various observation datasets. The observation data employed for these four rows correspond to PantheonPlus+SH0ES, PantheonPlus+SH0ES+GRB, PantheonPlus+SH0ES+GRB+OHD, and PantheonPlus+SH0ES+GRB+OHD+DESI, respectively. The shaded areas in dark grey and light grey are the confidence intervals of 1$\sigma$ and 2$\sigma$, respectively. The black dashed line represents the theoretical curve of the $\Lambda$CDM model.