In this set of papers the Dark Energy Spectroscopic Instrument (DESI) collaboration presents the second data release (DR2, three years of operation) of Baryon Acoustic Oscillation (BAO) scale measurements from the Lyman alpha forest spectra at redshifts ≲4.16 (key paper I), and from galaxies and quasars at redshifts <2 (key paper II). Results are based on a total of ~15 million galaxies and quasars. Cosmological implications are discussed in key paper II, favoring a time evolving equation of state with -1 < wₒ < 0. The supporting papers present detailed validation analyses, an extended dark energy analysis, and constraints specifically on neutrino physics.

M. Abdul Karim et al.,  Phys. Rev. D, 112, 083514 – Published 06 October, 2025

https://doi.org/10.1103/2wwn-xjm5

We present the Baryon Acoustic Oscillation (BAO) measurements with the Lyman-𝛼

 (Lyα) forest from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI) survey. Our BAO measurements include both the auto-correlation of the forest absorption observed in the spectra of high-redshift quasars and the cross-correlation of the absorption with the quasar positions. The total sample size is approximately a factor of two larger than the DR1 dataset, with forest measurements in over 820,000 quasar spectra and the positions of over 1.2 million quasars. We describe several significant improvements to our analysis in this paper, and two supporting papers describe improvements to the synthetic datasets that we use for validation and how we identify damped absorbers. Our main result is that we have measured the BAO scale with a statistical precision of 1.1% along and 1.3% transverse to the line of sight, for a combined precision of 0.65% on the isotropic BAO scale at zeff =2.33. This excellent precision, combined with recent theoretical studies of the BAO shift due to nonlinear growth, motivated us to include a systematic error term in BAO analysis for the first time. We measure the ratios 𝐷𝐻⁡(zeff)/𝑟𝑑 =8.632 ±0.098 ±0.026 and 𝐷𝑀⁡(zeff)/𝑟𝑑 =38.99 ±0.52 ±0.12, where 𝐷𝐻=𝑐/𝐻⁡(𝑧) is the Hubble distance, 𝐷𝑀 is the transverse comoving distance, 𝑟𝑑 is the sound horizon at the drag epoch, and we quote both the statistical and the theoretical systematic uncertainty. The companion paper presents the BAO measurements at lower redshifts from the same dataset and the cosmological interpretation.

M. Abdul Karim et al., Phys. Rev. D, 112, 083515 – Published 06 October, 2025

https://doi.org/10.1103/tr6y-kpc6

We present baryon acoustic oscillation (BAO) measurements from more than 14 million galaxies and quasars drawn from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2), based on three years of operation. For cosmology inference, these galaxy measurements are combined with DESI Lyman-𝛼 forest BAO results presented in a companion paper. The DR2 BAO results are consistent with DESI DR1 and SDSS, and their distance-redshift relationship matches those from recent compilations of supernovae (SNe) over the same redshift range. The results are well described by a flat 𝛬CDM model, but the parameters preferred by BAO are in mild, 2.3⁢𝜎 tension with those determined from the cosmic microwave background (CMB), although the DESI results are consistent with the acoustic angular scale θ∗ that is well-measured by Planck. This tension is alleviated by dark energy with a time-evolving equation of state parametrized by 𝑤0 and 𝑤𝑎, which provides a better fit to the data, with a favored solution in the quadrant with 𝑤0 > −1 and 𝑤𝑎⁢ < ⁢0. This solution is preferred over 𝛬CDM at 3.1⁢𝜎 for the combination of DESI BAO and CMB data. When also including SNe, the preference for a dynamical dark energy model over 𝛬CDM ranges from 2.8−4.2⁢𝜎 depending on which SNe sample is used. We present evidence from other data combinations which also favor the same behavior at high significance. From the combination of DESI and CMB we derive 95% upper limits on the sum of neutrino masses, finding ∑𝑚𝜈⁢ < 0.064 eV assuming 𝛬CDM and ∑𝑚𝜈⁢ < 0.16 eV in the 𝑤0⁢𝑤𝑎 model. Unless there is an unknown systematic error associated with one or more datasets, it is clear that 𝛬CDM is being challenged by the combination of DESI BAO with other measurements and that dynamical dark energy offers a possible solution.

A. Brodzeller et al., Phys. Rev. D, 112, 083510 – Published 06 October, 2025

https://doi.org/10.1103/wxyv-46kb

We present the Damped Ly𝛼 Toolkit for automated detection and characterization of Damped Ly𝛼 absorbers (DLA) in quasar spectra. Our method uses quasar spectral templates with and without absorption from intervening DLAs to reconstruct observed quasar forest regions. The best-fitting model determines whether a DLA is present while estimating the redshift and column density. With an optimized quality cut on detection significance (𝛥⁢𝜒2𝑟⁢ > ⁢0.03), the technique achieves an estimated 80% purity and 79% completeness when evaluated on simulated spectra with S/N > ⁢2 that are free of broad absorption lines (BAL). We provide a catalog containing candidate DLAs from the DLA Toolkit detected in DESI DR1 quasar spectra, of which 21,719 were found in S/N > ⁢2 spectra with predicted log10⁡(𝑁𝙷𝙸)⁢ > ⁢20.3 and detection significance 𝛥⁢𝜒2𝑟⁢ > 0.03. We compare the Damped Ly𝛼 Toolkit to two alternative DLA finders based on a convolutional neural network (CNN) and Gaussian process (GP) models. We present a strategy for combining these three techniques to produce a high-fidelity DLA catalog from DESI DR2 for the Ly𝛼 forest baryon acoustic oscillation measurement. The combined catalog contains 41,152 candidate DLAs with log10⁡(𝑁𝙷𝙸) ⁢> 20.3 from quasar spectra with S/N > ⁢2. We estimate this sample to be approximately 85% pure and 79% complete when BAL quasars are excluded.

W. Elbers et al. Phys. Rev. D, 112, 083513 – Published 06 October, 2025

https://doi.org/10.1103/w9pk-xsk7

The Dark Energy Spectroscopic Instrument (DESI) Collaboration has obtained robust measurements of baryon acoustic oscillations (BAO) in the redshift range, 0.1 < z < 4.2, based on the Lyman-α forest and galaxies from Data Release 2 (DR2). We combine these measurements with cosmic microwave background (CMB) data from Planck and the Atacama Cosmology Telescope to place our tightest constraints yet on the sum of neutrino masses. Assuming the cosmological ΛCDM model and three degenerate neutrino states, we find ∑𝑚𝜈 < 0.0642 eV (95%) with a marginalized error of σ(∑𝑚𝜈) = 0.020 eV. We also constrain the effective number of neutrino species, finding Neff = 3.23−0.34+0.35 (95%), in line with the Standard Model prediction. When accounting for neutrino oscillation constraints, we find a preference for the normal mass ordering and an upper limit on

the lightest neutrino mass of 𝑚l < 0.023 eV (95%). However, we determine using frequentist and Bayesian methods that our constraints are in tension with the lower limits derived from neutrino oscillations. Correcting for the physical boundary at zero mass, we report a 95% Feldman-Cousins upper limit of ∑𝑚𝜈 < 0.053 eV, breaching the lower limit from neutrino oscillations. Considering a more general Bayesian analysis with an effective cosmological neutrino mass parameter, ∑𝑚𝜈,eff, that allows for negative energy densities and removes unsatisfactory prior weight effects, we derive constraints that are in 3σ tension with the same oscillation limit, while the error rises to σ(∑𝑚𝜈,eff) = 0.053 eV. In the absence of unknown systematics, this finding could be interpreted as a hint of new physics not necessarily related to neutrinos. The preference of DESI and CMB data for an evolving dark energy model offers one possible solution. In the 𝑤0⁢𝑤𝑎CDM model, we find ∑𝑚𝜈 < 0.163 eV (95%), relaxing the neutrino tension. These constraints all rely on the effects of neutrinos on the cosmic expansion history. Using full-shape power spectrum measurements of Data

Release 1 (DR1) galaxies, we place complementary constraints that rely on neutrino free streaming. Our strongest such limit in ΛCDM, using selected CMB priors, is ∑𝑚𝜈 < 0.193 eV (95%).

K. Lodha et al., Phys. Rev. D, 112, 083511 – Published 06 October, 2025

https://doi.org/10.1103/w4c6-1r5j

We conduct an extended analysis of dark energy constraints, in support of the findings of the DESI DR2 cosmology key paper, including DESI data, Planck CMB observations, and three different supernova compilations. Using a broad range of parametric and non-parametric methods, we explore the dark energy phenomenology and find consistent trends across all approaches, in good agreement with the 𝑤0⁢𝑤𝑎CDM key paper results. Even with the additional flexibility introduced by non-parametric approaches, such as binning and Gaussian Processes, we find that extending 𝛬CDM to include a two parameter 𝑤⁡(𝑧) is sufficient to capture the trends present in the data. Finally, we examine three dark energy classes with distinct dynamics, including quintessence scenarios satisfying 𝑤 ≥ −1, to explore what underlying physics can explain such deviations. The current data indicate a clear preference for models that feature a phantom crossing; although alternatives lacking this feature are disfavored, they cannot yet be ruled out. Our analysis confirms that the evidence for dynamical dark energy, particularly at low redshift (𝑧 ≲ 0.3), is robust and stable under different modeling choices.

U. Andrade et al., Phys. Rev. D, 112, 083512 – Published 06 October, 2025

https://doi.org/10.1103/kdys-w8vl

The Dark Energy Spectroscopic Instrument (DESI) data release 2 (DR2) galaxy and quasar clustering data represents a significant expansion of data from DR1, providing improved statistical precision in BAO constraints across multiple tracers, including bright galaxies (BGS), luminous red galaxies (LRGs), emission line galaxies (ELGs), and quasars (QSOs). In this paper, we validate the BAO analysis of DR2. We present the results of robustness tests on the blinded DR2 data and, after unblinding, consistency checks on the unblinded DR2 data. All results are compared to those obtained from a suite of mock catalogs that replicate the selection and clustering properties of the DR2 sample. We confirm the consistency of DR2 BAO measurements with DR1 while achieving a reduction in statistical uncertainties due to the increased survey volume and completeness. The combined BAO precision, including both statistical and systematic errors, improves from∼0.52% in DR1 to 0.30% in DR2—a factor of 1.7 gain. We assess the impact of analysis choices, including different data vectors (correlation function vs. power spectrum), modeling approaches and systematics treatments, and an assumption of the Gaussian likelihood, finding that our BAO constraints are stable across these variations and assumptions with a few minor refinements to the baseline

setup of the DR1 BAO analysis [1]. We summarize a series of pre-unblinding tests that confirmed the readiness of our analysis pipeline, the final systematic errors, and the DR2 BAO analysis baseline. The successful completion of these tests led to the unblinding of the DR2 BAO measurements, ultimately leading to the DESI DR2 cosmological analysis, with their implications for the expansion history of the Universe and the nature of dark energy presented in the DESI key paper [2].

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