Héctor Gil-Marín

We evaluate the Baryon Acoustic Oscillation (BAO) signal in the bispectrum as a tool to detect and characterize the relative velocity effect. We extend the existing framework by presenting an updated model for the redshift-space tree-level bispectrum that comprehensively incorporates all relative velocity terms. We introduce a novel, unbiased technique to extract the isotropic BAO dilation parameter ( α _iso ) solely from the bispectrum monopole. Validated against N-body simulations, this template-based extraction successfully recovers the acoustic scale and enhances the statistical constraining power by ∼ 22% for a volume of 500 ( h ^-1 Gpc) ³ , when analyzed in tandem with the pre-reconstruction power spectrum, offering a powerful complement to standard post-reconstruction pipelines. We quantify how individual relative velocity components distort both two- and three-point statistics. We find that these effects induce distinct systematic shifts in the extracted α _iso between the two probes. We find systematic discrepancies of up to 2% for b _v ² = ±0.05 and up to 20% for b _δ ^bc ≤ -2. This differences demonstrate that a direct comparison of independent power spectrum and bispectrum BAO measurements can break parameter degeneracies and isolate the amplitude of these biases. Finally, we provide a concrete prescription to detect and constrain the three associated relative velocity bias parameters, showing that a joint analysis is highly sensitive to the b _v ² and b _δ ^bc amplitudes. This establishes the bispectrum BAO as a robust cosmological probe for current and next-generation galaxy surveys, serving both as a cross-check for standard analyses and a crucial diagnostic tool against systematic biases.

We derive cosmological parameter constraints from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 (DR1) galaxy clustering data, based on a joint full-shape analysis of the power spectrum multipoles and the bispectrum monopole using the ShapeFit framework [1]. This work is the follow-up of [2], which obtains for the first time constraints on the ShapeFit parameters using the bispectrum of DESI DR1, for the luminous red galaxy (LRG) and quasar (QSO) samples. Here we present the first ShapeFit cosmological inference results using the bispectrum of DESI DR1. For the baseline flat ΛCDM model, our analysis yields results broadly in agreement with previous studies of the DESI DR1 data-set. In particular, we recover values for the matter density parameter and Hubble constant of respectively Ω _m =0.310±0.012 and H ₀ =[68.92±0.97] km s ^-1 Mpc ^-1 , consistent with previous results from the full DESI DR1 dataset that did not use the bispectrum signal [3]. The inclusion of the bispectrum significantly tightens the constraints on the amplitude of fluctuations, reducing the error-bars in ln(A_s×10 ¹⁰ ) by approximately 20%, compared to using the power spectrum alone. We also explore extended cosmological models by performing fits for the evolving dark energy equation of state w ₀ w _a , and the sum of neutrino masses ∑ m _ν . In these cases, we obtain constraints slightly larger than the ones from previous works from the DESI collaboration [4], due to not combining the full-shape results with other probes in all tracers. We find no strong evidence of deviations from standard ΛCDM, with the dark energy equation-of-state remaining within 2σ from a cosmological constant Λ, and the neutrino mass being consistent with the normal hierarchy, ∑ m _ν <0.1 [eV] at 95% confidence limit. These constraints are broadly consistent with other DESI DR1 analyses, thus validating the robustness of the ShapeFit compression approach and the inclusion of the bispectrum for cosmological inference.

We reconstruct the primordial power spectrum P _ℛ (k) from the BOSS DR 12 LRG and eBOSS DR 16 QSO catalogs with a non-parametric Bayesian method. The P _ℛ (k) is reconstructed by linearly interpolating N knots in the {log k, log P _ℛ (k) } plane. We use a parametric model to describe the galaxy power spectra of the BOSS+eBOSS catalogs, assuming any power-law deviations and BAO contributions separately from the matter power spectrum template, composed of seven parameters Θ _model . This parametric model enables us to reconstruct P _ℛ(k) at non-linear scales, reaching k = 0.3 h Mpc ^-1 . The method is validated by applying it to different Primordial Features (PF) templates and by recovering the input power law of MD-Patchy and EZmock mock catalogs, representative of the BOSS and eBOSS data. These mocks provide additional information on Θ _model , enabling us to impose Gaussian correlated priors on Θ _model . This prior set allows us to reconstruct P _ℛ (k) more precisely and to alleviate the degeneracies between the model and knot parameters. The results for both individual and combined z-bins and galactic caps of the BOSS and eBOSS catalogs are consistent, showing no evidence of the presence of PF in P _ℛ (k) and pointing to a quasi-scale-invariant power law as the preferred model for P _ℛ (k), as predicted by most slow-roll inflationary models. With a different prior set that relaxes the Gaussian constraints on Θ _model and imposes Planck-based priors on the extreme knots, the results also favor the power law. From the knot reconstructions, we robustly constrain the spectral index n _s = 0.976 ± 0.021, compatible with the Planck value.

Analyses of baryon acoustic oscillations (BAO) commonly employ template-based methods to extract compressed parameters from the clustering of dark-matter tracers, which are then interpreted in terms of ratios of the sound-horizon scale and cosmological distances relative to a fiducial cosmology. A small mismatch between the sound-horizon scale derived from the standard analytic formulation (integral over the sound speed) and the effective scale imprinted in clustered matter can, however, introduce a systematic bias in cosmological inference. We extend previous work to a broader class of cosmological models, quantify this bias for surveys with DESI-like precision, and propose strategies to correct for the effect. We find that the induced bias becomes a significant fraction of the statistical uncertainty for deviations from the fiducial cosmology, at the level of |ΔΩ _m | = 0.03 and |ΔN _eff| = 0.3, and for very precise data corresponding to a forecasted Year-5 DESI survey (or other stage IV dark energy galaxy surveys). We present several ways to correct for this effect, suitable for a variety of applications. We therefore recommend that analyses exploring such parameter regimes either apply the proposed corrections or include an appropriate systematic error budget.

We present a cosmological analysis combining full-shape (FS) clustering measurements from the Dark Energy Spectroscopic Instrument (DESI) DR1 with baryon acoustic oscillation (BAO) measurements from DESI DR2. To achieve a robust combination that accounts for the correlation between the two data releases, we employ the ShapeFit compression method and estimate the joint covariance using EZmocks. This compressed approach inherently mitigates the prior volume effects that have previously dominated Bayesian constraints from DESI data with minimal external priors. Consequently, we obtain — for the first time within a Bayesian framework — reliable DESI-only constraints on extensions to ΛCDM using only a Big Bang Nucleosynthesis prior on the baryon density and a wide prior on the spectral index. In flat ΛCDM, we find Ω _m = 0.3035 ± 0.0085, h = 0.6876 ± 0.0059, and σ ₈ = 0.822 ± 0.034. For the w ₀ w _a CDM dynamical dark energy model, we measure w ₀ = -0.49 ± 0.25 and w _a = -1.52 ± 0.77, improving constraints by ∼ 30% relative to the analogous DR1 measurement and reducing the discrepancy with ΛCDM to 1.4 σ when compared to BAO only analyses. We also report competitive limits on the sum of neutrino masses and spatial curvature. This work demonstrates that the ShapeFit compression provides a prior-robust and computationally efficient pathway to constrain beyond-ΛCDM physics with large-scale structure.

We assess the impact of the fiducial cosmology choice on cosmological inference from full-shape (FS) fits of the galaxy power spectrum in the DESI 2024 Data Release 1 (DR1). Using a suite of AbacusSummit DR1 mock catalogues based on the Planck 2018 best-fit cosmology, we quantify potential systematic shifts introduced by analysing the data under five secondary cosmologies — featuring variations in matter density, thawing dark energy, higher effective number of neutrino species, reduced clustering amplitude, and the DESI DR1 BAO best-fit w ₀ w _a CDM cosmology — relative to DESI's baseline Planck 2018 cosmology. We investigate two complementary FS analysis approaches: full-modelling (FM) and ShapeFit (SF), each with distinct sensitivities to the assumed fiducial model. Across all tracers, we find for FM that systematic shifts induced by fiducial cosmology mismatches remain well below the DESI DR1 statistical uncertainties, with maximum deviations of 0.22 σ _DR1 in ΛCDM scenarios and 0.12 σ _DR1+SN when including SN Ia mock data in extended w ₀ w _a CDM fits. For SF, the shifts in the compressed parameters remain below 0.45 σ _DR1 for all tracers and cosmologies.

In 2021 May the Dark Energy Spectroscopic Instrument (DESI) collaboration began a 5 yr spectroscopic redshift survey to produce a detailed map of the evolving three-dimensional structure of the Universe between z = 0 and z ≈ 4. DESI’s principal scientific objectives are to place precise constraints on the equation of state of dark energy, the gravitationally driven growth of large-scale structure, and the sum of the neutrino masses, and to explore the observational signatures of primordial inflation. We present DESI DR1, which consists of all data acquired during the first 13 months of the DESI main survey, as well as a uniform reprocessing of the DESI Survey Validation data, which were previously made public in the DESI Early Data Release. The DR1 main survey includes high-confidence redshifts for 18.7M objects, of which 13.1M are spectroscopically classified as galaxies, 1.6M as quasars, and 4M as stars, making DR1 the largest sample of extragalactic redshifts ever assembled. We summarize the DR1 observations, the spectroscopic data-reduction pipeline and data products, large-scale structure catalogs, value-added catalogs, and describe how to access and interact with the data. In addition to fulfilling its core cosmological objectives with unprecedented precision, we expect DR1 to enable a wide range of transformational astrophysical studies and discoveries.

Context. The direct empirical determination of the local value of the Hubble constant ( H ₀ ) has markedly advanced thanks to improved instrumentation, measurement techniques, and distance estimators. However, combining determinations from different estimators is nontrivial due to their correlated calibrations and different analysis methodologies. Aims. Using covariance weighting and leveraging community expertise, we have constructed a rigorous and transparent “Distance Network” to find a consensus value and uncertainty for the locally measured Hubble constant. Methods. Experts across all relevant distance measurement domains were invited to critically review the available datasets spanning parallaxes, detached eclipsing binaries, masers, Cepheids, the tip of the red giant branch, Miras, carbon-rich asymptotic giant branch stars, Type Ia (SNe Ia) and Type II supernovae, surface brightness fluctuations, the fundamental plane, and Tully–Fisher relations. Before any calculations, the group voted for first-rank indicators to define a “baseline” Distance Network. Other indicators were included to assess the robustness and sensitivity of the results. We provide open-source software and data products to support full transparency and future extensions of this effort. Results. Our key findings are as follows: (1) The local H ₀ is robustly determined, with first-rank indicators internally consistent within their uncertainties. (2) A covariance-weighted combination yields a relative uncertainty of 1.1% (baseline) or 0.9% (all estimators). (3) The contribution from SNe Ia is consistent across compilations of optical or NIR magnitudes. (4) Removing either Cepheids or the tip of the red giant branch has a minimal effect on the central value of H ₀ . (5) Replacing SNe Ia with galaxy-based indicators changes H ₀ by less than 0.1 km s ⁻¹ Mpc ⁻¹ while doubling its uncertainty. (6) The baseline result is H ₀ = 73.50 ± 0.81 km s ⁻¹ Mpc ⁻¹ , 7.1 σ from the early Universe plus ΛCDM result 67.24 ± 0.35 km s ⁻¹ Mpc ⁻¹ and 5.0 σ from BBN+BAO within a flat ΛCDM DESI DR2 (68.51 ± 0.58 km s ⁻¹ Mpc ⁻¹ ). Conclusions. A networked approach, such as the one presented here, is invaluable for enabling further progress in Hubble constant measurements, as it provides the much needed advances in accuracy and precision without overreliance on any single method, sample, or group.

In this work, we test a framework to analyse redshift-space distortions in configuration and Fourier space simultaneously. We tested our methods with the AbacusSummit suite of N -body simulations as well as a more numerous set of approximate EZmocks, and reproduced the sample of luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) and its extension (eBOSS). Our clustering models are based on the effective field theory of large-scale structures in a Lagrangian frame, which is used in the latest results from the Dark Energy Spectroscopic Instrument. We performed a template type of analysis, including dilation parameters and the slope parameter from the ShapeFit framework. We find that the joint space inference yields unbiased and robust constraints on simulated datasets that are consistent with the results from individual spaces or previous methods to obtain consensus results. Our joint space analysis on the BOSS+eBOSS LRG sample obtains fσ ₈ = 0.463 ± 0.052, which is in good agreement with the official 2020 results.