arXiv subjects

Licia Verde

Publications and source records attributed to Licia Verde.

At least 19 recordsLinked to original sources

arXiv2026

Reaching the Metallicity Floor at $z\sim 10$: Lensed Star Clusters at Cosmic Dawn and Cosmic Noon

Origins of globular clusters (GCs) are linked to the assembly of their host galaxies. We analyze star-cluster populations in two strongly lensed systems that bracket Cosmic Dawn and Cosmic Noon: the Cosmic Gems arc (GEMS) at z=9.625, among the first galaxies, and the Sparkler at z=1.378. New STARRED deconvolution photometry of GEMS provides SEDs for ten unique, doubly imaged cluster candidates, while a homogeneous Bayesian analysis places both populations on a common cosmological timeline. The GEMS clusters formed at $z_{\rm form}\approx 10$--$11$ (median $\simeq10.2$), consistent with halo assembly at or above the atomic-cooling scale. Their photometry requires low metallicities: individual clusters are consistent with $[Z/{\rm H}] \lesssim -1.2$, and the data exclude $[Z/{\rm H}]\geq-0.5$, though they cannot distinguish reliably below $[Z/{\rm H}] \simeq -1.5$. This conclusion is unchanged when using stellar-population models including binary evolution---important for ultraviolet emission at this age---yielding similarly low metallicities, $[Z/{\rm H}]=-2.2$ to $-2.7$. The formal estimate, $[Z/{\rm H}] = -2.3\pm0.3$, is consistent with the Milky Way GC metallicity floor, though its value remains prior-dependent. The Sparkler clusters formed $\sim2.5$ Gyr later, at $z_{\rm form}\approx 2$--$3.5$ in a Cosmic Noon dwarf galaxy, and are more enriched ($[Z/{\rm H}] \approx -0.5$). Comparison with Milky Way GCs places GEMS in an exceptionally early, metal-poor regime and the Sparkler among later, more enriched populations, though neither association uniquely determines an in-situ or ex-situ origin. Closed-box and gas-regulator calculations show both systems are compatible with limited pre-enrichment followed by rapid enrichment and accretion-regulated growth. Together, they probe distinct cluster-forming environments from Cosmic Dawn to Cosmic Noon.

astro-ph.GA↗

arXiv2026

Cosmic CORALS: Timing the Universe with high-z star clusters

In this work, we explore the potential of anchoring the age-redshift relation across cosmic time by probing the oldest star clusters at high redshift, now observed thanks to the James Webb Space Telescope in strongly lensed fields. As a case study, we consider one of the highest-redshift systems observed, the Cosmic Gems arc at $z=9.625$. We perform image deconvolution of multi-band JWST imaging, identifying a total of 20 point sources along the arc. We derive the stellar ages through a cosmology-independent spectral energy distribution (SED) fitting framework, ensuring that these measurements can be used as unbiased cosmological anchors. By combining these high-z systems with state-of-the-art local globular cluster ages, we perform a joint Bayesian fit to the age-redshift relation in a flat $\Lambda$CDM model, measuring $H_0=70^{+27}_{-16}\ \rm{km\ s^{-1}\ Mpc^{-1}}$ and $\Omega_m=0.33^{+0.37}_{-0.21}$. While these constraints are still loose, we show that the slope of the degeneracy, a power-law in the $\Omega_m - H_0$ plane, is highly dependent on the redshift of the sources, becoming shallower as redshift increases. Leveraging this geometric rotation, we present forecasts showing that a future sample of $\sim 300$ lensed proto-globular clusters well-distributed up to $z \approx 10$ could tighten the statistical precision to $4\%$ on $H_0$ and $11\%$ on $\Omega_m$, competitive with and independent of methods currently in use. The present work, therefore, represents a new avenue in cosmology and comes at a timely moment, when JWST observes high-redshift lensed star clusters routinely, Euclid and the Nancy Grace Roman Space Telescope uncover new strong lensing fields, and close to the start of operation of the ESO Extremely Large Telescope.

astro-ph.CO↗

arXiv2026

Bispectrum BAO and the baryon-dark matter relative velocity

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 ($\alpha_{\rm iso}$) 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 $\sim30\%$, 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 $\alpha_{\rm iso}$ between the two probes. We find systematic discrepancies of up to $2\%$ for $b_{v^2}=\pm0.05$ and up to $20\%$ for $b_{\delta^{bc}}\le-2$. 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 $b_{\delta^{bc}}$ 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.

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arXiv2026

Deep Learning for Astrophysics: An Open Textbook from the NASA Cosmic Origins AI/ML Science and Technology Interest Group

Recent community assessments identify education as a principal barrier to adopting modern machine learning in astronomy. We present Deep Learning for Astrophysics, a freely available textbook at https://deeplearning4astro.com, curated from the NASA Cosmic Origins Artificial Intelligence and Machine Learning Science and Technology Interest Group (AI/ML STIG) lecture series. The book collects 23 chapters by 17 lecturers across six parts, moving from computational foundations and deep-learning architectures through generative modeling, simulation-based inference, reinforcement learning, and large-language-model agents to the practice of AI-laden science. Many include executable notebooks using astronomical data.

astro-ph.IM↗

arXiv2026

AI Scientists as Engines of Discovery: A Case for Development within Reformed Institutions

Agentic artificial intelligence (AI) systems are beginning to assist, accelerate, and partially automate scientific discovery, performing tasks that span literature synthesis, code generation, data analysis, hypothesis proposal, and model criticism. We argue that this transition is qualitative rather than incremental, and that suitably designed multi-agent systems may evolve from passive computational tools into ``AI scientists'' that can expand the hypothesis-generating and verification capacity of science. Such systems must be developed and deployed within a scientific ecosystem fit for purpose: institutions must be redesigned for verification, accountability, interpretability, and dual-use safety. We sketch how multi-agent architectures, illustrated by the prototype framework \textit{Denario}, accelerate the discovery cycle and traverse model spaces beyond human reach; examine what this implies for authorship, peer review, and the enduring role of human scientists; and close with recommendations for governing AI as an epistemic actor rather than a mere instrument.

cs.AI↗

arXiv2026

From Evidence to Evident: Decisive Cosmological Evidence for the Normal Neutrino Mass Hierarchy

Cosmological data have reached the precision needed to turn the neutrino mass ordering from a weak Bayesian preference into a decisive model-selection test. We compute the evidence for the Normal and Inverted Hierarchies by combining DESI DR2 clustering with NuFIT oscillation data. In baseline $\Lambda$CDM, DESI DR2 plus Planck CamSpec gives $\Sigma m_\nu<0.0642\,{\rm eV}$ at 95\% confidence, close to the normal-ordering floor, $\Sigma m_\nu^{\rm NH}\simeq0.059\,{\rm eV}$, but well below the inverted-ordering minimum, $\Sigma m_\nu^{\rm IH}\simeq0.099\,{\rm eV}$. Thus the inverted hierarchy lies in the tail of the cosmological likelihood. The Bayes factor $K=P(D|{\rm NH})/P(D|{\rm IH})$ exceeds $460$ even for a conservative reference prior, and remains strong, $K>40$, in baseline-model extensions. We show that this result is robust to the choice between a reference prior and a physically motivated logarithmic hierarchical prior, marking the transition from {\em prior-sensitive evidence} to {\em likelihood-dominated exclusion} of the inverted hierarchy within standard cosmology. Embedding these priors in the two-dimensional design space of measure (logarithmic versus linear in mass) and structure (hierarchical versus non-hierarchical), we find that all four prior constructions give decisive evidence under DESI DR2, with residual prior dependence governed mainly by the measure -- a factor $\sim\!10$ in $K$ -- rather than by the hierarchy assumption. At the prior-family level, the evidence favors the SJPV prior predictive over HS by a Bayes factor above $4,700$ across each matched-support variation tested. The favored normal ordering pushes the effective Majorana mass to the few-meV regime, with median $m_{\beta\beta}=3.28\,{\rm meV}$ and 95\% credible interval $0.95<m_{\beta\beta}<11.55\,{\rm meV}$, below the inverted-ordering target for upcoming neutrinoless double-beta decay experiments.

astro-ph.CO↗

arXiv2026

The Coherence Principle: A Falsifiable Prior for Model Selection from the Grammar of Theories

Bayesian model selection in cosmology and particle physics is often performed where posterior odds inherit a strong, often unacknowledged dependence on the prior assigned to competing models. Standard responses -- reference priors, hierarchical priors, or appeals to naturalness -- ignore relevant theoretical knowledge or rely on criteria hard to define operationally. We propose the \emph{Coherence Principle}: a reproducible prescription for assigning model priors according to compatibility with the validated structure of an existing theory. This structure, or \emph{grammar}, includes symmetries, conservation laws, locality, Lorentz invariance, and universality patterns. Unmotivated violations of these rules incur a coherence cost, converted into a prior weight through a maximum-entropy exponential form controlled by one calibratable parameter $\alpha$. The resulting prior is distinct from both the Bayesian Occam factor and naturalness: it penalizes not parameter volume or fine tuning, but departures from validated theoretical grammar. We illustrate the principle with examples from cosmology and fundamental physics: neutrino mass mechanisms, dark energy and modified gravity, inflation, beyond-Standard-Model sectors, and hierarchical astrophysical inference. We test it also on four historical cases -- general relativity, Pauli's neutrino, parity violation, and special relativity -- where evidential and theoretical contexts can be reconstructed. These examples show that it favors the historically successful choice when the proper grammar is defined in the correct domain and time. The Coherence Principle makes explicit a common but usually tacit part of physical reasoning: trust in validated structural rules. It turns this judgment into a transparent, testable, and overrulable component of Bayesian inference, leaving empirical likelihoods free to dominate when data are sufficiently constraining.

astro-ph.CO↗

arXiv2026

The Age of the Universe with Globular Clusters IV: Multiple Stellar Populations

We revisit the determination of the age of the Universe from galactic globular clusters, extending previous analyses by explicitly accounting for the presence of multiple stellar populations within each cluster. Using high--quality \textit{Hubble Space Telescope} color--magnitude diagrams for 69 globular clusters, we relax the standard single--population assumption, and model two stellar populations with independent ages, metallicities, helium abundances, and population fractions. The inference is performed using the full color--magnitude diagram morphology, an explicit treatment of field contamination, and a hierarchical framework that propagates non--Gaussian age posteriors. Allowing for multiple stellar populations has a negligible impact on globular cluster age estimates. The ages of the oldest populations remain fully consistent with those obtained under the single--population assumption, with differences at the $0.6\sigma$ level. Restricting to the metal--poor subsample ([Fe/H] $< -1.5$), we infer a dominant old component with mean age $t_{\rm GC}=13.61\pm0.25\,\mathrm{(stat)}\,\pm0.23 \mathrm{(sys)}\,\mathrm{Gyr}$. Adopting a conservative delay between the Big Bang and the formation of the first globular clusters, we obtain an age of the Universe of $t_{\rm U}=13.81\pm0.25\,\mathrm{(stat)}\,\pm0.23 \mathrm{(sys)}\,\mathrm{Gyr}$. In addition to age constraints, our analysis yields simultaneous measurements of metallicity and helium content for the different populations, including constraints on helium enrichment and population fractions which are consistent with independent determinations from the literature. These results demonstrate that globular--cluster--based cosmic chronometry is robust to stellar population complexity, reinforcing its role as a precise and largely cosmological model--independent probe of the age of the Universe.

astro-ph.GA↗

arXiv2026

The BAO scale -- how standard is the standard ruler?

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 $|\Delta \Omega_m| = 0.03$ and $|\Delta N_\mathrm{eff}| = 0.3$, 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.

astro-ph.CO↗

arXiv2026

The Atacama Cosmology Telescope: Constraints on Local Non-Gaussianity from the ACT Cluster Catalog

We derive constraints on local-type primordial non-Gaussianity using the ACT DR6 Sunyaev--Zel'dovich cluster catalog. Modeling the redshift- and mass-dependent number counts of 1,201 clusters in the 10,347~deg$^2$ Legacy region, and accounting for survey completeness, intrinsic SZ scatter, and a weak-lensing-calibrated mass bias, we compute theoretical abundances using the Log--Edgeworth halo mass function. Assuming $\Lambda$CDM with well-motivated external priors, we obtain $f_{\rm NL} = 55 \pm 125$ (68% CL), consistent with Gaussian initial conditions. These constraints probe comoving scales of $5$--$10~{\rm Mpc}~h^{-1}$, complementing CMB bispectrum and scale-dependent bias measurements, which do not reach such small scales. We also find evidence for a 16.4% residual mass bias, which, although heavily informed by our adopted priors, plays a key role in matching observed and predicted counts but has negligible effect on $f_{\rm NL}$ constraints. We briefly discuss robustness of the results under relaxed priors and the prospects for next-generation SZ and lensing surveys to strengthen cluster-based tests of primordial non-Gaussianity.

astro-ph.CO↗

arXiv2025

The Local Distance Network: a community consensus report on the measurement of the Hubble constant at 1% precision

The direct, empirical determination of the local value of the Hubble constant (H0) has markedly advanced thanks to improved instrumentation, measurement techniques, and distance estimators. However, combining determinations from different estimators is non-trivial, due to correlated calibrations and different analysis methodologies. Using covariance weighting and leveraging the broad and comprehensive community of experts, we constructed a rigorous and transparent Distance Network (DN) to find a consensus value and uncertainty for the local H0. All critically reviewed the available data sets, spanning parallaxes, detached eclipsing binaries, masers, Cepheids, the TRGB, Miras, JAGB stars, SN Ia, Surface Brightness Fluctuations, SN II, the Fundamental Plane, and Tully-Fisher relations and voted for indicators to define a `baseline' DN and others to assess robustness and sensitivity of the results. We provide open-source software and data products to support full transparency and future extensions of this effort. Our conclusions: 1) Local H0 is robustly determined, with first-rank indicators internally consistent within their uncertainties; 2) A covariance-weighted combination yields an uncertainty of 1.1% (baseline) or 0.9% (all estimators); 3) The contribution from SNe Ia is consistent across four current compilations of optical magnitudes or using NIR-only magnitudes; 4) Removing either Cepheids or TRGB has minimal effect; 5) Replacing SNe Ia with galaxy-based indicators changes H0 by less than 0.1 km/s/Mpc, while doubling its uncertainty; 6) The baseline result is H0=73.50+/-0.81 km/s/Mpc. Compared to early Universe results, our result differs by 7.1sigma from flat {\Lambda}CDM with Planck+SPT+ACT and 5.0 sigma with BBN+BAO (DESI2). A networked approach is invaluable for enabling further progress in accuracy and precision without overreliance on any single method, sample or group.

astro-ph.CO↗

arXiv2025

$\texttt{GENGARS}$: Accurate non-Gaussian initial conditions with arbitrary bispectrum for N-body simulations

Primordial non-Gaussianity is predicted by various inflationary models, and N-body simulations are a crucial tool for studying its imprints on large-scale structure. In this work, we present \texttt{GENGARS} ( GEnerator of Non-Gaussian ARbitrary Shapes), a framework for generating accurate non-Gaussian initial conditions for N-body simulations. It builds upon the formulation introduced by Wagner \& Verde (2012), enabling to generate a primordial gravitational potential with a desired separable bispectrum $B_{\Phi}(k_1,k_2,k_3)$. For the local, equilateral and orthogonal non-Gaussian templates, we benchmark our method against the well-established \texttt{2LPT-PNG} code. We show that \texttt{GENGARS} achieves improved accuracy and lower noise by suppressing spurious contributions to the primordial power spectrum. This paper aims at presenting the method, quantifying its performance and illustrating the benefits and applicable use cases over existing approaches.

astro-ph.CO↗

arXiv2025

Smooth sailing or ragged climb? -- Increasing the robustness of power spectrum de-wiggling and ShapeFit parameter compression

The baryonic features in the galaxy power spectrum offer tight, time-resolved constraints on the expansion history of the Universe but complicate the measurement of the broadband shape of the power spectrum, which also contains precious cosmological information. In the context of ShapeFit, the broadband information is compressed into a single parameter, the slope of the power spectrum at the pivot scale, $m$, is sensitive to matter-radiation equality and the baryonic suppression. To calculate this parameter, two steps are necessary: 1) smoothing the power spectrum to remove the baryonic oscillations and 2) calculating the derivative of the power spectrum ratio at the pivot scale. In this work we compare thirteen methods designed to separate the broadband and oscillating components and examine their performance. The systematic uncertainty between different de-wiggling procedures is at most $2$%, depending on the scale. For the obtained slope, we show that the de-wiggling procedures impart large 50% differences, but as long as the theory and data pipelines are consistent, this is of no concern for cosmological inference given the precision of existing and ongoing surveys. However, it still motivates the search for more robust ways of extracting the slope. We show that post-processing the power spectrum ratio before taking the derivative makes the slope values far more robust. We further investigate eleven ways of extracting the slope and highlight the two most successful ones. We derive a systematic uncertainty on the slope $m$ of $\sigma_{m,\mathrm{syst}} = 0.023 |m| + 0.001$ by studying the behavior of the slopes in different cosmologies and the impact in cosmological inference. In cosmologies with a feature in the matter-power spectrum, such as in the early dark energy cosmologies, this systematic uncertainty estimate does not necessarily hold, and further investigation is required.

astro-ph.CO↗

arXiv2025

The Age of the Universe with Globular Clusters III: Gaia distances and hierarchical modeling

This is the third article in a series aimed at computing accurate and precise ages of galactic globular clusters from their full color-magnitude diagram in order to estimate the age of the Universe and in turn constrain the cosmological model. We update previous constraints using additional data and an improved methodology which allows us to vary the helium abundance and the reddening law in addition to the usual parameters (age, metallicity, alpha enhancement, distance and absorption) in the analysis. Even with the additional degrees of freedom, using the full color-magnitude diagram, now described as a Gaussian mixture Bayesian hierarchical model, a tight constraint on the age(s) of the globular clusters and on the other parameters can be obtained, and the statistical errors are fully subdominant to the systematic errors. We find that the age of the oldest globular clusters is $t_{\rm GC} = 13.39 \pm 0.10 ({\rm stat.}) \pm 0.23 ({\rm sys.})$ Gyr, resulting in an age of the Universe $t_{\rm U}=13.57^{+ 0.16}_{-0.14} ({\rm stat})\pm 0.23 ({\rm sys.})$ and a robust 95\% confidence upper limit of $t_U^{\leq}=13.92_{-0.1}^{+0.13}({\rm stat}) \pm{0.23} ({\rm sys})$. This is fully compatible with our previous estimates and with the model-dependent, Cosmic Microwave Background-derived age for the Universe of $t_{\rm U} =13.8 \pm 0.02$ Gyr for a $\Lambda$CDM model.

astro-ph.CO↗

arXiv2024

Time to Sparkler. Accurate ages of lensed globular clusters at $z=1.4$ with JWST photometry

Determining reliable ages for old stellar objects at different redshifts offers a powerful means to constrain cosmology without relying on a specific cosmological model: this is known as the cosmic clocks method. Globular clusters (GCs), long recognised as hosts of the Universe's oldest stars, have served as the archetypical cosmic clocks. However, their age estimates have traditionally been confined to redshift z=0, limiting their role to constraining the present-day age of the Universe. Here we explore how to measure reliable ages of GCs well beyond $z=0$, leveraging their potential to extend cosmic clock measurements to earlier epochs. Specifically, we use 6-band JWST/NIRCam high-precision photometry of candidate stellar clusters in the Sparkler galaxy, located at redshift $z$=1.378 and strongly lensed by the galaxy cluster SMACS J0723.3-7327. By employing stellar population models within a Bayesian inference framework, we constrain the GCs' ages, star formation histories, metallicities, and dust attenuation. The five compact sources previously identified as GCs, based on their red spectral energy distributions being consistent with the colours of old stellar systems, yield a formation age of $1.9\pm0.4$ Gyr on average. This result implies a total age of the Universe that aligns well with the $\Lambda$CDM model derived from Planck18 data. Recent space-based observations have uncovered a wealth of lensed GCs as well as globulars within the member galaxies of the clusters themselves. These findings suggest that the pool of objects available for cosmic clock studies is enormous. A systematic multi-band photometric survey of GCs in and behind galaxy clusters, using facilities like Euclid and JWST, would therefore be a powerful tool for estimating cluster ages across a large range of redshifts, allowing the Universe to be dated across an unprecedented range of epochs.

astro-ph.GA↗

arXiv2024

Testing the robustness of the BAO determination in the presence of massive neutrinos

We study the robustness of the Baryon Acoustic Oscillation (BAO) feature in galaxy clustering in the presence of massive neutrinos. In the standard BAO analysis pipeline a reference cosmological model is assumed to boost the BAO peak through the so-called reconstruction technique and in the modelling of the BAO feature to extract the cosmological information. State-of-the art spectroscopic BAO measurements, such as the Dark Energy Spectroscopic Instrument claim an aggregate precision of 0.52$\%$ on the BAO scale, with a systematic error of 0.1$\%$ associated to the assumption of a reference cosmology when measuring and analyzing the BAO feature. While the systematic effect induced by this arbitrary choice of fiducial cosmology has been studied for a wide range of $\Lambda$CDM-like models, it has not yet been tested for reference cosmologies with massive neutrinos with the precision afforded by next generation surveys. In this context, we employ the Quijote high-resolution dark-matter simulations with haloes above a mass of $M\sim 2\times10^{13} h^{-1}M_{\odot}$, with different values for the total sum of neutrinos masses, $\sum m_\nu[{\rm eV}] = 0,\, 0.1,\, 0,2,\, 0.4$ to study and quantify the impact of the pipeline's built-in assumption of massless neutrinos on the measurement of the BAO signal, with a special focus on the BAO reconstruction technique. We determine that any additional systematic bias introduced by the assumption of massless neutrinos is no greater than $0.1\%$ ($0.2\%$) for the isotropic (anisotropic) measurement. We expect these conclusions also hold for galaxies provided that neutrino properties do not alter the galaxy-halo connection.

astro-ph.CO↗

arXiv2024

Cosmological simulations of scale-dependent primordial non-Gaussianity

We present the results of a set of cosmological N-body simulations with standard $\Lambda$CDM cosmology but characterized by a scale-dependent primordial non-Gaussianity of the local type featuring a power-law dependence of the $f_{\rm NL}^{\rm loc}(k)$ at large scales followed by a saturation to a constant value at smaller scales where non-linear growth leads to the formation of collapsed cosmic structures. Such models are built to ensure consistency with current Cosmic Microwave Background bounds on primordial non-Gaussianity yet allowing for large effects of the non-Gaussian statistics on the properties of non-linear structure formation. We show the impact of such scale-dependent non-Gaussian scenarios on a wide range of properties of the resulting cosmic structures, such as the non-linear matter power spectrum, the halo and sub-halo mass functions, the concentration-mass relation, the halo and void density profiles, and we highlight for the first time that some of these models might mimic the effects of Warm Dark Matter for several of such observables

astro-ph.CO↗

arXiv2024

BAO cosmology in non-spatially flat background geometry from BOSS+eBOSS and lessons for future surveys

We study the impact of the assumption of a non-flat fiducial cosmology on the measurement, analysis and interpretation of BAO distance variables, along and across the line-of-sight. The assumption about cosmology enters in the choice of the base template, as well as on the transformation of tracer's redshifts into distances (the catalog cosmology): here we focus on the curvature assumption, separately and jointly, on both. We employ BOSS and eBOSS publicly available data and show that for the statistical precision of this data set, distance measures and thus cosmological inference are robust to assumptions about curvature both of the template and the catalog. Thus the usual assumptions of flat fiducial cosmologies (but also assumptions of non-flat cosmologies) do not produce any detectable systematic effects. For forthcoming large-volume surveys, however, small but appreciable residual systematic shifts can be generated which may require some care. These are mostly driven by the choice of catalog cosmology if it is significantly different from true cosmology. In particular, the catalog (and template) cosmology should be chosen, possibly iteratively, in such a way that the recovered BAO scaling variables are sufficiently close to unity. At this level of precision, however, other previously overlooked effects become relevant, such as a mismatch between the sound horizon as seen in the BAO and the actual sound horizon in the early Universe. If unaccounted for, such effect may be misinterpreted as cosmological and thus bias the curvature (and cosmology) constraints. We present best practices to avoid this.

astro-ph.CO↗