Evidence of dynamical dark energy found via the DESI DR2 Lyman$\alpha$ forest

TL;DR

This study analyzes DESI DR2 Lyman-alpha forest BAO data combined with other cosmological observations, finding evidence that supports a dynamical dark energy scenario over the standard cosmological constant model.

Contribution

It provides the first comprehensive analysis of multiple dark energy parameterizations using DESI DR2 data combined with various cosmological datasets.

Findings

All models favor a dynamical dark energy with $w_0 > -1$, $w_a < 0$.

Moderate preference for dynamical dark energy over $ ext{Lambda}$CDM, up to 3.10$\sigma$ with Ly$oldsymbol{ extalpha}$ + CMB + galaxy BAO.

Preference for models varies with dataset combination, with some datasets showing strong evidence for specific models.

Abstract

We present a comprehensive analysis of the cosmological implications of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) Lyman-$\alpha$ forest baryon acoustic oscillation (BAO) measurements, combined with DESI DR2 galaxy BAO, Type Ia supernova samples (Pantheon$^+$, DES-Dovekie, and Union3), and the cosmic microwave background CamSpec likelihood. We consider several dark-energy parameterizations, including Chevallier-Polarski-Linder, logarithmic, exponential, Jassal-Bagla-Padmanabhan, Barboza-Alcaniz, and generalized emergent dark energy, as well as the $w$CDM model and non-flat extensions of $\Lambda$CDM and $w$CDM. Using the Metropolis-Hastings MCMC algorithm, we constrain cosmological parameters and compute Bayesian evidence with \texttt{MCEvidence}. We find that non-flat extensions remain consistent with spatial flatness, with $\Omega_k \approx 0$. All parameterizations favor a dynamical dark-energy scenario with $w_0 > -1$, $w_a < 0$, and $w_0 + w_a < -1$, consistent with a Quintom-B behavior. A moderate preference for dynamical dark-energy models is found relative to $\Lambda$CDM, reaching up to $\sim3.10\sigma$ for Ly$\alpha$ + CMB + galaxy BAO. When combined with SNe~Ia datasets, the deviations decrease to $\lesssim2\sigma$, corresponding to inconclusive preference. The Bayes factor ($\ln B_{ij}$) shows that model preference depends strongly on the dataset combination: $w$CDM and o$w$CDM exhibit moderate evidence for Ly$\alpha$ + CMB + galaxy BAO, while most other models show weak or inconclusive evidence. With Pantheon$^{+}$ or DES-Dovekie, o$w$CDM shows strong evidence, whereas other models remain moderately favored.