Search

The squeezed cross-bispectrum $B_{\kappa ,\mathrm{Ly}\alpha }$ between the gravitational lensing in the cosmic microwave background and the 1D $\mathrm{Ly}\alpha$ forest power spectrum can constrain bias parameters and break degeneracies between ${\sigma }_8$ and other cosmological parameters. We detect $B_{\kappa ,\mathrm{Ly}\alpha }$ with $4.8\sigma$ significance at an effective redshift $z_{\mathrm{eff}}=2.4$ using Planck PR3 lensing map and over 280,000 quasar spectra from the Dark Energy Spectroscopic Instrument’s first-year data. We test our measurement against metal contamination and foregrounds such as Galactic extinction and clusters of galaxies by deprojecting the thermal Sunyaev-Zeldovich effect. We compare our results to a tree-level perturbation theory calculation and find reasonable agreement between the model and measurement.

The determination of the direction of a stellar core collapse via its neutrino emission is crucial for the identification of the progenitor for a multimessenger follow-up. A highly effective method of reconstructing supernova directions within the Deep Underground Neutrino Experiment (DUNE) is introduced. The supernova neutrino pointing resolution is studied by simulating and reconstructing electron-neutrino charged-current absorption on ${}^{40}\mathrm{Ar}$ and elastic scattering of neutrinos on electrons. Procedures to reconstruct individual interactions, including a newly developed technique called “brems flipping,” as well as the burst direction from an ensemble of interactions are described. Performance of the burst direction reconstruction is evaluated for supernovae happening at a distance of 10 kpc for a specific supernova burst flux model. The pointing resolution is found to be 3.4 degrees at 68% coverage for a perfect interaction-channel classification and a fiducial mass of 40 kton, and 6.6 degrees for a 10 kton fiducial mass respectively. Assuming a 4% rate of charged-current interactions being misidentified as elastic scattering, DUNE’s burst pointing resolution is found to be 4.3 degrees (8.7 degrees) at 68% coverage.

We present an alternative measurement of the Baryon Acoustic Oscillation (BAO) using the Legendre multipole representation of the Lyman-$\alpha$ forest correlation functions from the second data release (DR2) of the Dark Energy Spectroscopic Instrument survey. Compressing the autocorrelation and cross-correlation functions into Legendre multipoles yields a positive-definite covariance matrix without any smoothing—unlike the baseline DR2 analysis—thanks to a significantly reduced data vector size. We introduce the statistical corrections required to debias the finite-sample covariance matrix estimate and demonstrate that monopole and quadrupole terms for both autocorrelations and cross-correlations can be used even when the correlation functions are distorted by continuum errors and contaminated by metals. This formalism has slightly diminished the constraining power of the BAO scale, while considerably weakening constraints on nuisance parameters. We measure the isotropic BAO scale with 0.93% precision at $z_{\mathrm{eff}}=2.35$, the Hubble parameter $H(z_{\mathrm{eff}})=(239.5\pm 3.4)(147.09\mathrm{Mpc}/r_d)\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, and the transverse comoving distance $D_M(z_{\mathrm{eff}})=(5.80\pm 0.10)(r_d/147.09\mathrm{Mpc})\mathrm{Gpc}$ for a given value of the sound horizon ($r_d$). Our BAO results are entirely consistent with the baseline DR2 analysis.

We present the Damped $\mathrm{Ly}\alpha$ Toolkit for automated detection and characterization of damped $\mathrm{Ly}\alpha$ absorbers (DLAs) 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 HI column density. With an optimized quality cut on detection significance ($\mathrm{\Delta }{\chi }_r^2>0.03$), the technique achieves an estimated 80% purity and 79% completeness when evaluated on simulated spectra with $\mathrm{S}/\mathrm{N}>2$ that are free of broad absorption lines (BALs). We provide a catalog containing candidate DLAs from the DLA Toolkit detected in DESI DR1 quasar spectra, of which 21 719 were found in $\mathrm{S}/\mathrm{N}>2$ spectra with predicted ${\log }_{10}(N_{\mathtt{HI}})>20.3$ and detection significance $\mathrm{\Delta }{\chi }_r^2>0.03$. We compare the Damped $\mathrm{Ly}\alpha$ Toolkit to two alternative DLA finders based on a convolutional neural network and Gaussian process models. We present a strategy for combining these three techniques to produce a high-fidelity DLA catalog from DESI DR2 for the $\mathrm{Ly}\alpha$ forest baryon acoustic oscillation measurement. The combined catalog contains 41 152 candidate DLAs with ${\log }_{10}(N_{\mathtt{HI}})>20.3$ from quasar spectra with $\mathrm{S}/\mathrm{N}>2$. We estimate this sample to be approximately 85% pure and 79% complete when BAL quasars are excluded.

We report cosmological results from the Dark Energy Spectroscopic Instrument (DESI) measurements of baryon acoustic oscillations (BAO) when combined with recent data from the Atacama Cosmology Telescope (ACT). By jointly analyzing ACT and Planck data and applying conservative cuts to overlapping multipole ranges, we assess how different $Planck+\mathrm{ACT}$ dataset combinations affect consistency with DESI. While ACT alone exhibits a tension with DESI exceeding $3\sigma$ within the $\mathrm{\Lambda }\mathrm{CDM}$ model, this discrepancy is reduced when ACT is analyzed in combination with Planck. For our baseline DESI DR2 $\mathrm{BAO}+Planck$ $\mathrm{P}\mathrm{R}4+\mathrm{ACT}$ likelihood combination, the preference for evolving dark energy over a cosmological constant is about $3\sigma$, increasing to over $4\sigma$ with the inclusion of type Ia supernova data. While the dark energy results remain quite consistent across various combinations of Planck and ACT likelihoods with those obtained by the DESI collaboration, the constraints on neutrino mass are more sensitive, ranging from $\sum m_{\nu }<0.061\mathrm{eV}$ in our baseline analysis, to $\sum m_{\nu }<0.077\mathrm{eV}$ (95% confidence level) in the CMB likelihood combination chosen by ACT when imposing the physical prior $\sum m_{\nu }>0\mathrm{eV}$.

Measurements of electrons from ${\nu }_e$ interactions are crucial for the Deep Underground Neutrino Experiment (DUNE) neutrino oscillation program, as well as searches for physics beyond the standard model, supernova neutrino detection, and solar neutrino measurements. This article describes the selection and reconstruction of low-energy (Michel) electrons in the ProtoDUNE-SP detector. ProtoDUNE-SP is one of the prototypes for the DUNE far detector, built and operated at CERN as a charged particle test beam experiment. A sample of low-energy electrons produced by the decay of cosmic muons is selected with a purity of 95%. This sample is used to calibrate the low-energy electron energy scale with two techniques. An electron energy calibration based on a cosmic ray muon sample uses calibration constants derived from measured and simulated cosmic ray muon events. Another calibration technique makes use of the theoretically well-understood Michel electron energy spectrum to convert reconstructed charge to electron energy. In addition, the effects of detector response to low-energy electron energy scale and its resolution including readout electronics threshold effects are quantified. Finally, the relation between the theoretical and reconstructed low-energy electron energy spectra is derived, and the energy resolution is characterized. The low-energy electron selection presented here accounts for about 75% of the total electron deposited energy. After the addition of lost energy using a Monte Carlo simulation, the energy resolution improves from about 40% to 25% at 50 MeV. These results are used to validate the expected capabilities of the DUNE far detector to reconstruct low-energy electrons.

The Deep Underground Neutrino Experiment (DUNE) will produce world-leading neutrino oscillation measurements over the lifetime of the experiment. In this work, we explore DUNE’s sensitivity to observe charge-parity violation (CPV) in the neutrino sector, and to resolve the mass ordering, for exposures of up to 100 kiloton-megawatt-calendar years (kt-MW-CY), where calendar years include an assumption of 57% accelerator uptime based on past accelerator performance at Fermilab. The analysis includes detailed uncertainties on the flux prediction, the neutrino interaction model, and detector effects. We demonstrate that DUNE will be able to unambiguously resolve the neutrino mass ordering at a $4\sigma$ ($5\sigma$) level with a 66 (100) kt-MW-CY far detector exposure, and has the ability to make strong statements at significantly shorter exposures depending on the true value of other oscillation parameters, with a median sensitivity of $3\sigma$ for almost all true ${\delta }_{\mathrm{CP}}$ values after only 24 kt-MW-CY. We also show that DUNE has the potential to make a robust measurement of CPV at a $3\sigma$ level with a 100 kt-MW-CY exposure for the maximally CP-violating values ${\delta }_{\mathrm{CP}}=\pm \pi /2$. Additionally, the dependence of DUNE’s sensitivity on the exposure taken in neutrino-enhanced and antineutrino-enhanced running is discussed. An equal fraction of exposure taken in each beam mode is found to be close to optimal when considered over the entire space of interest.

In this work we use Lagrangian perturbation theory to analyze the harmonic space galaxy clustering signal of the Bright Galaxy Survey (BGS) and luminous red galaxies (LRGs) targeted by the dark energy spectroscopic instrument (DESI), combined with the galaxy-galaxy lensing signal measured around these galaxies using Dark Energy Survey Year 3 source galaxies. The BGS and LRG galaxies are extremely well characterized by DESI spectroscopy and, as a result, lens galaxy redshift uncertainty and photometric systematics contribute negligibly to the error budget of our “$2\times 2$-point” analysis. On the modeling side, this work represents the first application of the spinosaurus code, implementing an effective field theory model for galaxy intrinsic alignments, and we additionally introduce a new scheme (maiar) for marginalizing over the large uncertainties in the redshift evolution of the intrinsic alignment signal. Furthermore, this is the first application of a hybrid effective field theory model for galaxy bias based on the aemulus $\nu$ simulations. Our main result is a measurement of the amplitude of the lensing signal, $S_8={\sigma }_8{({\mathrm{\Omega }}_m/0.3)}^{0.5}=0.850_{-0.050}^{+0.042}$, consistent with values of this parameter derived from the primary cosmic microwave background. This constraint is artificially improved by a factor of 51% if we assume a more standard, but restrictive parametrization for the redshift evolution and sample dependence of the intrinsic alignment signal, and 63% if we additionally assume the nonlinear alignment model. We show that when fixing the cosmological model to the best-fit values from Planck PR4 there is $>5\sigma$ evidence for a deviation of the evolution of the intrinsic alignment signal from the functional form that is usually assumed in cosmic shear and galaxy-galaxy lensing studies.

Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at $z\lesssim 1$ disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to future cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel’dovich (kSZ) effect from the Atacama Cosmology Telescope, stacked on the luminous red galaxy sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date; we detect the signal at $13\sigma$, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the “missing baryon” problem.

We present updated constraints on the parameters of an axion dark energy model, for which we took into account the properties of its characteristic potential and its full cosmological evolution. We show that the values of the axion parameters appear sufficiently constrained by the data, including the latest DESI DR1, and are consistent with the theoretical expectations of a field mass $m_a$ in the ultralight regime $\log (m_a{c}^2/\mathrm{eV})\simeq -32.60\pm 0.12$, and an effective energy scale $f_a$ close to the reduced Planck energy $\log (f_a/M_{\mathrm{Pl}})\simeq -0.28\pm 0.19$. Our results also support the idea of dynamical dark energy, although Bayesian evidence still favors the phenomenological dark energy model $w_0{w}_a$ over the axion dark energy, with the Bayes factor indicating moderate and weak strength of the evidence, respectively, when the models are compared to the cosmological constant $\mathrm{\Lambda }$. However, the results suggest that axion dark energy remains a well-motivated model and its parameters may be better constrained if the upcoming DESI data show further evidence for dynamical dark energy.

We present a measurement of the pairwise kinematic Sunyaev-Zel’dovich (kSZ) signal using the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Sample (BGS) Data Release 1 (DR1) galaxy sample overlapping with the Atacama Cosmology Telescope (ACT) CMB temperature map. Our analysis makes use of 1.6 million galaxies with stellar masses $\log M_{\star }/M_{\odot }>10$, and we explore measurements across a range of aperture sizes (${2.1}^{\prime }<{\theta }_{\mathrm{ap}}<{3.5}^{\prime }$) and stellar mass selections. This statistic directly probes the velocity field of the large-scale structure, a unique observable of cosmic dynamics and modified gravity. In particular, at low redshifts, this quantity is especially interesting, as deviations from General Relativity are expected to be largest. Notably, our result represents the highest-significance low-redshift ($z\sim 0.3$) detection of the kSZ pairwise effect yet. In our most optimal configuration (${\theta }_{\mathrm{ap}}={3.3}^{\prime }$, $\log M_{\star }>11$), we achieve a $5\sigma$ detection. Assuming that an estimate of the optical depth and galaxy bias of the sample exists via e.g., external observables, this measurement constrains the fundamental cosmological combination $H_{0}f{\sigma }_8^2$. A key challenge is the degeneracy with the galaxy optical depth. We address this by combining CMB lensing, which allows us to infer the halo mass and galaxy population properties, with hydrodynamical simulation estimates of the mean optical depth, $\overline{\tau }$. We stress that this is a proof-of-concept analysis; with BGS DR2 data we expect to improve the statistical precision by roughly a factor of two, paving the way toward robust tests of modified gravity with kSZ-informed velocity-field measurements at low redshift.

The parity-odd four-point function provides a unique probe of fundamental symmetries and potential new physics in the large-scale structure of the Universe. We present measurements of the parity-odd four-point function using the Dark Energy Spectroscopic Instrument (DESI) DR1 luminous red galaxy (LRG) sample and assess its detection significance. Our analysis considers both auto- and cross-correlations, using two complementary approaches to the covariance: (i) the full analytic covariance matrix applied to the uncompressed data vector, and (ii) a compressed data vector combined with a hybrid covariance matrix constructed from simulations and analytic estimates. When using the full analytic covariance matrix without corrections, we observe apparent auto-correlation signals with significance up to $4\sigma$. However, this excess is also consistent with a mismatch between the statistical fluctuations estimated from the simulations and those present in the real data. Our findings therefore suggest that the parity-odd signal in the current DESI DR1 LRG sample is consistent with zero. We note, however, that the low completeness of this sample may have a non-negligible impact on the detection sensitivity. Future data releases with improved completeness will be crucial for further investigation.

ProtoDUNE Single-Phase (ProtoDUNE-SP) is a 770-ton liquid argon time projection chamber that operated in a hadron test beam at the CERN Neutrino Platform in 2018. We present a measurement of the total inelastic cross section of charged kaons on argon as a function of kaon energy using 6 and $7\mathrm{GeV}/c$ beam momentum settings. The flux-weighted average of the extracted inelastic cross section at each beam momentum setting was measured to be $380\pm 26\mathrm{mbarns}$ for the $6\mathrm{GeV}/c$ setting and $379\pm 35\mathrm{mbarns}$ for the $7\mathrm{GeV}/c$ setting.

In this paper, we study scalar mediator induced nonstandard interactions (SNSIs) in the context of the ESSnuSB experiment. In particular, we study the capability of ESSnuSB to put bounds on the SNSI parameters and also study the impact of SNSIs in the measurement of the leptonic $CP$ phase ${\delta }_{CP}$. Existence of SNSIs modifies the neutrino mass matrix and this modification can be expressed in terms of three diagonal real parameters (${\eta }_{ee}$, ${\eta }_{\mu \mu }$, and ${\eta }_{\tau \tau }$) and three off-diagonal complex parameters (${\eta }_{e\mu }$, ${\eta }_{e\tau }$, and ${\eta }_{\mu \tau }$). Our study shows that the upper bounds on the parameters ${\eta }_{\mu \mu }$ and ${\eta }_{\tau \tau }$ depend upon how $\mathrm{\Delta }{m}_{31}^2$ is minimized in the theory. However, this is not the case when one tries to measure the impact of SNSIs on ${\delta }_{CP}$. Further, we show that the $CP$ sensitivity of ESSnuSB can be completely lost for certain values of ${\eta }_{ee}$ and ${\eta }_{\mu \tau }$ for which the appearance channel probability becomes independent of ${\delta }_{CP}$.

The Dark Energy Spectroscopic Instrument (DESI) is a massively parallel spectroscopic survey on the Mayall telescope at Kitt Peak, which has released measurements of baryon acoustic oscillations determined from over 14 million extragalactic targets. We combine DESI Data Release 2 with CMB datasets to search for evidence of matter conversion to dark energy (DE), focusing on a scenario mediated by stellar collapse to cosmologically coupled black holes (CCBHs). In this physical model, which has the same number of free parameters as $\mathrm{\Lambda }\mathrm{CDM}$, DE production is determined by the cosmic star formation rate density (SFRD), allowing for distinct early- and late-time cosmologies. Using two SFRDs to bracket current observations, we find that the CCBH model: accurately recovers the cosmological expansion history, agrees with early-time baryon abundance measured by BBN, reduces tension with the local distance ladder, and relaxes constraints on the summed neutrino mass $\sum m_{\nu }$. For these SFRDs, we find a peaked positive $\sum m_{\nu }<0.149\mathrm{eV}$ (95% confidence) and $\sum m_{\nu }={0.106}_{-0.069}^{+0.050}\mathrm{eV}$, respectively, in good agreement with lower limits from neutrino oscillation experiments. A peak in $\sum m_{\nu }>0$ results from late-time baryon consumption in the CCBH scenario and is expected to be a general feature of any model that converts sufficient matter to dark energy during and after reionization.

The peak of the matter power spectrum, known as the turnover (TO) scale, is determined by the horizon size at the time of matter-radiation equality. This scale can serve as a standard ruler, independent of other features in the matter power spectrum, such as baryon acoustic oscillations (BAO). Here, we present the first detection of the turnover in the galaxy autopower spectrum, utilizing the distribution of quasars and luminous red galaxies (LRG) measured by the Dark Energy Spectroscopic Instrument (DESI) during its first year of survey operations in a model-independent manner. To avoid confirmation bias, we first analyze the data using data blinding methods designed for the DESI baryon acoustic oscillation, redshift space distortion and scale-dependent bias signals. We measure the angle-averaged dilation distance $D_{\mathrm{V}}(z=1.651)=(38.1\pm 2.5)r_{\mathrm{H}}$ from the quasars and $D_{\mathrm{V}}(z=0.733)=(21.8\pm 1.0)r_{\mathrm{H}}$ from the LRG sample in units of the horizon $r_{\mathrm{H}}$ at the matter-radiation-equality epoch. Combining these two constraints and assuming a flat $\mathrm{\Lambda }\mathrm{CDM}$ model with three standard neutrino species, we can translate this into a constraint of ${\mathrm{\Omega }}_{\mathrm{m}}{h}^2=0.139_{-0.046}^{+0.036}$. We can break the ${\mathrm{\Omega }}_{\mathrm{m}}\text{−}{H}_0$ degeneracy with low-redshift distance measurements from type-Ia supernova (SN) data from $\mathrm{Pantheon}+$, we obtain a sound-horizon free estimate of the Hubble-Lemaître parameter of $H_0={65.2}_{-6.2}^{+4.9}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, consistent with sound-horizon dependent DESI measurements. On the other hand, combining the DESI BAO and TO, we find a truly DESI-only measurement of $H_0={74.0}_{-3.5}^{+7.2}\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, in line with DESI-only full-shape results where the sound-horizon scale is marginalized out. This discrepancy in $H_0$ can be reconciled in a $w_0{w}_a\mathrm{CDM}$ cosmology, where the combination of DESI BAO and TO data yields $H_0=66.5\pm 7.2\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$.

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-$\alpha$ forest BAO results presented in a companion paper (M. Abdul-Karim et al., companion paper, Phys. Rev. D 112, 083514 2025.). The DR2 BAO results are consistent with DESI DR1 and the Sloan Digital Sky Survey, 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 $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model, but the parameters preferred by BAO are in mild, $2.3\sigma$ tension with those determined from the cosmic microwave background (CMB), although the DESI results are consistent with the acoustic angular scale ${\theta }_{*}$ that is well measured by Planck. This tension is alleviated by dark energy with a time-evolving equation of state parametrized by $w_0$ and $w_a$, which provides a better fit to the data, with a favored solution in the quadrant with $w_0>-1$ and $w_a<0$. This solution is preferred over $\mathrm{\Lambda }\mathrm{CDM}$ at $3.1\sigma$ for the combination of DESI BAO and CMB data. When also including SNe, the preference for a dynamical dark energy model over $\mathrm{\Lambda }\mathrm{CDM}$ ranges from $2.8-4.2\sigma$ 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 $\sum m_{\nu }<0.064\mathrm{eV}$ assuming $\mathrm{\Lambda }\mathrm{CDM}$ and $\sum m_{\nu }<0.16\mathrm{eV}$ in the $w_0{w}_a$ model. Unless there is an unknown systematic error associated with one or more datasets, it is clear that $\mathrm{\Lambda }\mathrm{CDM}$ is being challenged by the combination of DESI BAO with other measurements and that dynamical dark energy offers a possible solution.

We present the baryon acoustic oscillation (BAO) measurements with the Lyman-$\alpha$ ($\mathrm{Ly}\alpha$) forest from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI) survey. Our BAO measurements include both the autocorrelation of the $\mathrm{Ly}\alpha$ 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 2 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 $\mathrm{Ly}\alpha$ 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 $z_{\mathrm{eff}}=2.33$. 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 $\mathrm{Ly}\alpha$ BAO analysis for the first time. We measure the ratios $D_H(z_{\mathrm{eff}})/r_d=8.632\pm 0.098\pm 0.026$ and $D_M(z_{\mathrm{eff}})/r_d=38.99\pm 0.52\pm 0.12$, where $D_H=c/H(z)$ is the Hubble distance, $D_M$ is the transverse comoving distance, $r_d$ 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.

We present a measurement of the non-Gaussian four-point correlation function (4PCF) from the DESI DR1 luminous red galaxy (LRG) sample. For the gravitationally induced parity-even 4PCF, we detect a signal with a significance of $14.7\sigma$ using our fiducial setup. We assess the robustness of this detection through a series of validation tests, including auto and cross-correlation analyses, sky partitioning across multiple patch combinations, and variations in radial scale cuts. Due to the low completeness of the sample, we find that differences in fiber assignment implementation schemes can significantly impact estimation of the covariance and introduce biases in the data vector. After correcting for these effects, all tests yield consistent results. This is one of the first measurements of the connected 4PCF on the DESI LRG sample; the good agreement between the simulation and the data implies that the amplitude of the density fluctuation inferred from the connected 4PCF is consistent with the Planck $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. The methodology and diagnostic framework established in this work provide a foundation for interpreting parity-odd 4PCF.

The second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI), containing data from the first three years of observations, doubles the number of Lyman-$\alpha$ ($\mathrm{Ly}\alpha$) forest spectra in DR1 and it provides the largest dataset of its kind. To ensure a robust validation of the baryonic acoustic oscillation (BAO) analysis using $\mathrm{Ly}\alpha$ forests, we have made significant updates compared to DR1 to both the mocks and the analysis framework used in the validation. In particular, we present CoLoRe-QL, a new set of $\mathrm{Ly}\alpha$ mocks that use a quasilinear input power spectrum to incorporate the nonlinear broadening of the BAO peak. We have also increased the number of realizations used in the validation to 400, compared to the 150 realizations used in DR1. Finally, we present a detailed study of the impact of quasar redshift errors on the BAO measurement, and we compare different strategies to mask damped Lyman-$\alpha$ absorbers in our spectra. The BAO measurement from the $\mathrm{Ly}\alpha$ dataset of DESI DR2 is presented in a companion publication.