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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.

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.

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.

The Dark Energy Spectroscopic Instrument (DESI) Collaboration has obtained robust measurements of baryon acoustic oscillations in the redshift range $0.1<z<4.2$, based on the Lyman-$\alpha$ forest and galaxies from data release 2. 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 $\mathrm{\Lambda }\mathrm{CDM}$ model and three degenerate neutrino states, we find $\sum m_{\nu }<0.0642\mathrm{eV}$ (95%) with a marginalized error of $\sigma (\sum m_{\nu })=0.020\mathrm{eV}$. We also constrain the effective number of neutrino species, finding $N_{\mathrm{eff}}=3.23_{-0.34}^{+0.35}$ (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 $m_l<0.023\mathrm{eV}$ (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 $\sum m_{\nu }<0.053\mathrm{eV}$, breaching the lower limit from neutrino oscillations. Considering a more general Bayesian analysis with an effective cosmological neutrino mass parameter, $\sum m_{\nu ,\mathrm{eff}}$, that allows for negative energy densities and removes unsatisfactory prior weight effects, we derive constraints that are in $3\sigma$ tension with the same oscillation limit, while the error rises to $\sigma (\sum m_{\nu ,\mathrm{eff}})=0.053\mathrm{eV}$. 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 $w_0{w}_a\mathrm{CDM}$ model, we find $\sum m_{\nu }<0.163\mathrm{eV}$ (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 galaxies, we place complementary constraints that rely on neutrino free streaming. Our strongest such limit in $\mathrm{\Lambda }\mathrm{CDM}$, using selected CMB priors, is $\sum m_{\nu }<0.193\mathrm{eV}$ (95%).

We conduct an extended analysis of dark energy constraints, in support of the findings of the Dark Energy Spectroscopic Instrument (DESI) second data release cosmology key paper, including DESI data, Planck cosmic microwave background observations, and three different supernova compilations. Using a broad range of parametric and nonparametric methods, we explore the dark energy phenomenology and find consistent trends across all approaches, in good agreement with the $w_0{w}_a\mathrm{CDM}$ (cold dark matter) key paper results. Even with the additional flexibility introduced by nonparametric approaches, such as binning and Gaussian processes, we find that extending $\mathrm{\Lambda }\mathrm{CDM}$ 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 $w\ge -1$, 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 ($z\lesssim 0.3$), is robust and stable under different modeling choices.

The Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) galaxy and quasar clustering data represents a significant expansion of data from Data Release 1 (DR1), providing improved statistical precision in baryon acoustic oscillation (BAO) constraints across multiple tracers, including bright galaxies, luminous red galaxies, emission line galaxies, and quasars. 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 with 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 $\sim 0.52\%$ 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. 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 (companion paper).

The synthesis of thin films of magnetic topological materials is necessary to achieve novel quantized Hall effects and electrodynamic responses. $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$ is a recently predicted topological axion insulator that has an antiferromagnetic ground state and an inverted band structure, but has only been synthesized and studied as a single crystal. We report on the synthesis of $c$-axis-oriented $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$ films on sapphire substrates by molecular beam epitaxy. By carefully tuning the substrate temperature during growth, we stabilize the Zintl phase of $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$ expected to be topologically nontrivial. The magnetic properties of these films reproduce those seen in single crystals, but their resistivity is enhanced when grown at lower temperatures. We additionally find that the magnetoresistance of $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$ is negative even up to fields as high as 31 T. While it is highly anisotropic at low fields, it becomes nearly isotropic at high magnetic fields above 5 T. Overall, the transport characteristics of $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$ appear similar to those of chalcogenide topological insulators, motivating the development of devices to gate tune the Fermi energy and reveal topological features in quantum transport.

Comparison is made between the mass quadrupole coordinate collective model and an appropriately extended version of the hydrodynamic collective model to ascertain whether or not the former is an exact microscopic formulation of the latter. We find that, while there are strong similarities, it is not.

NUCLEAR STRUCTURE Bohr-Mottelson model, hydrodynamic model, mass quadrupole collective model; comparison, theory.