arXiv subjects

Carlos A. P. Bengaly

Publications and source records attributed to Carlos A. P. Bengaly.

At least 19 recordsLinked to original sources

arXiv2026

Testing Statistical Isotropy in the FRB Sky Distribution: A Selection-Function-Aware Framework

We perform a test of statistical isotropy in the Universe using the sky distribution of fast radio bursts (FRBs), based on a compilation of $4066$ events detected by multiple surveys. Our method is based on the two-point angular correlation function $w(θ)$ as in the Landy--Szalay estimator, together with a tomographic absolute-anisotropy statistic, and estimates their observational uncertainties from complementary jackknife and bootstrap resampling. Both estimators are confronted with hierarchical ensembles of isotropic mock catalogs that propagate the uncertainties of empirically reconstructed survey selection functions, as well as the Poisson fluctuations of the isotropic realizations. The significances are obtained from a covariance-aware, SVD-regularized $χ^2$ statistic calibrated empirically against the mock ensemble, and we evaluate four nested scenarios that progressively incorporate a Galactic-plane mask and the survey selection functions. As for our results, we find that the raw FRB sky is strongly inconsistent with isotropy; Galactic masking alone reduces the tension by only a factor of $\sim 3$, whereas the selection functions reduce it by nearly four orders of magnitude, showing that the apparent anisotropy is driven by the highly non-uniform sky coverage of the contributing surveys, overwhelmingly dominated by CHIME. Only when both effects are combined we obtain that the observed distribution is fully consistent with statistical isotropy. This result is independently corroborated by the absolute-anisotropy estimator, and is stable under variations of the analysis parameters. Therefore, we find that the FRB sky distribution is consistent with statistical isotropy, helping confirm one of the main predictions of the standard model scenario.

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arXiv2026

On the bin sensitivity of the transverse BAO

We investigate the transverse BAO projection effect caused by redshift binning uncertainty ($z_c$). For SKA HI and DESI LRG surveys, we compare Gaussian, top-hat, and semi-Gaussian bins over widths $0.01<σ_z<0.1$, and propose a statistical correction using adjacent redshifts. The semi-Gaussian bin best recovers the BAO signal for $σ_z<0.04$, despite higher shot noise. Constraints are survey-dependent: Gaussian binning is weakest for SKA, while for DESI semi-Gaussian is tightest for $σ_z<0.04$ (otherwise comparable). The semi-Gaussian scheme offers the optimal balance between cosmological parameter constraints and BAO fidelity, making it robust for multi-probe analyses.

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arXiv2026

Morphological Bias: How Ellipticals and Spirals Trace the Cosmic Web Differently

We present a data-driven measurement of galaxy bias and scale-dependent relative bias for elliptical and spiral galaxies using angular auto- and cross-power spectra from DES and DESI Legacy Imaging Surveys DR8. We introduce the cross-tracer clustering ratio (CTCR), which uses the ratio of auto- to cross-power spectra to isolate the relative clustering of morphological tracers as a function of angular multipole $\ell$. Across both surveys, ellipticals are more strongly clustered than spirals; the cleanest CTCR constraints come from DESI, where the two morphological samples have better-matched redshift distributions. The difference is scale dependent: the relative bias is close to unity on large angular scales, $\ell \lesssim 50$, but increases toward smaller scales, reaching an average separation of $2.6σ$ at $\ell \sim 150-200$. A complementary linear-bias analysis confirms that ellipticals are positively biased relative to the matter field, while spirals are consistent with weak bias or anti-bias. Unlike narrowly selected LRG samples, our morphologically selected elliptical samples show little redshift evolution, consistent with a broader halo-mass distribution. The results are robust to two covariance estimators, contamination tests, luminosity splits, and comparisons with two N-body mock catalogs. These new findings provide empirical evidence that galaxy morphology imprints both the amplitude and scale dependence of galaxy bias, and establish CTCR as a useful observable for testing halo occupation and assembly-bias models with future imaging surveys.

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arXiv2026

Revisiting the CMB homogeneity scale: low multipoles removal effect and extragalactic foreground masking

The Cosmic Microwave Background (CMB) reaches homogeneity at relatively modest angular scales compared to the expectation of the standard $Λ$CDM model revealing an important challenge to the theoretical predictions. We analyze this inconsistency through the homogeneity scale $H$ and the slope of the homogeneity index at $θ= 90^\circ$. We find that the removal of low multipoles, in particular the quadrupole, from both the data and the $Λ$CDM synthetic CMB maps, significantly improve the consistency between models and observations. This adds to indications of the relevant contribution of the low value of the CMB quadrupole to the observed anomalies in the homogeneity scale. Due to the presence of a new extragalactic foreground in the CMB maps, we have performed statistical analyses with different masking taking into account the regions mostly affected. In particular we consider galaxies in the local neighborhood which are expected to affect more significantly the large angular scales. We find that by masking these regions, the analysis cannot solve the discrepancy between the observations and the $Λ$CDM model in spite of a small improvement of their mutual consistency. The studies with both foreground masking and low-$\ell$ removed CMB maps show similar results than those of the full CMB map indicating that the main discrepancy between theory and observations is associated to the quadrupole anomaly and may require more exhaustive analysis.

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arXiv2026

Cosmic homogeneity: the effect of redshift-space distortions and bias and cosmological constraints

We present a novel cosmological analysis based on the angular correlation dimension $D_2$ curve, a cumulative statistic derived from the two-point correlation function. Unlike traditional 3D approaches, angular $D_2$ is inherently less sensitive to nonlinear dynamical distortions, such as the small-scale Finger-of-God (FoG) effect. Using both MultiDark-Patchy and EZmock galaxy catalogs, we assess the scale-dependent impact of redshift-space distortions on $D_2$ and bias measurements. We demonstrate that the systematic errors associated with FoG modeling can be significantly reduced by restricting the analysis to appropriate minimum comoving angular scales of $\sim 1.25^{\circ} $, which corresponding to physical scales of $18$-$23\,h^{-1}\,\mathrm{Mpc}$ over the redshift range $0.46 \leq z \leq 0.74$ within the standard $Λ$CDM model. Since the observational estimative of $D_2(θ)$ is not dependent on a cosmological model we obtain robust estimates of the galaxy bias and place competitive constraints on the physical matter density $ω_m$. By applying this framework to SDSS DR12 and DR16 Luminous Red Galaxy data, we obtain $ω_m = 0.137^{+0.041}_{-0.059}$ (1$σ$), which agrees with current CMB analyses. Our results highlight the potential of the angular $D_2$ curve as a model-independent and robust tool for cosmological parameter inference.

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arXiv2026

Measurements of the Angular Homogeneity Scale from DESI DR1

The study of the large-scale distribution of galaxies provides essential information for testing the standard cosmological model, namely the $Λ$CDM paradigm. This scenario is based upon two foundations: General Relativity as the theory of gravity, and the Cosmological Principle, which states that the Universe is statistically homogeneous and isotropic on large scales -- so that we can measure distances and ages in the Universe assuming the FLRW metric. In this work, we perform a test of the Cosmological Principle by probing the angular homogeneity scale, $θ_H$, using the state-of-the-art observational data of Luminous Red Galaxies (LRGs) from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1). Our analysis is performed exclusively in two dimensions, across narrow redshift ranges inside a larger redshift sample of $0.4 < z < 1.1$, in two different surveyed regions of the sky (North and South Galactic Caps), as we want to minimize a priori dependences on an underlying cosmological model. We obtain that such a scale is indeed identified in all redshift ranges, and that they are consistent with mock simulations assuming the $Λ$CDM model. Moreover, our results are in great agreement with previous measurements using Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey Data Release 16 (SDSS-IV eBOSS DR16), as well as between the north and south galactic caps of the DESI DR1 survey. These findings help underpinning statistical isotropy and homogeneity of the Universe as a physically valid hypothesis in light of upcoming stage-IV redshift surveys, hence are consistent with one of the fundamental pillars of the standard cosmological model.

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arXiv2026

Confirming the uniformity of the Hubble flow with Pantheon+ Supernovae

According to the perturbed Friedmann model, the difference between Hubble constant measurements in two rest frames, at leading order in velocity, is determined solely by the relative motion of the observers and remains unaffected by the peculiar velocities of the sources. This implies that, when averaging over a sufficiently large and distant set of sources where local nonlinear inhomogeneities are diminished, such a difference should vanish, so that the Hubble flow is statistically uniform, as predicted by the Cosmological Principle -- a core assumption of the standard cosmological paradigm. In previous works, distance measurement compilations, e.g. the CosmicFlows-3 catalogue, were used for this purpose, as it comprises a large number ($\sim 10^4$) of sources of different types. Due to the increasing amount of precise luminosity distance measurements of Type Ia Supenovae (SNe) in the last few years, in this work we investigate whether we can confirm the uniformity of the Hubble flow with low-$z$ SN distances only. By means of the Pantheon+ and SH0ES compilation, we find that the results align well with previous works based on the CF3 catalogue, and are in good agreement with the expected Hubble variance in the standard model across cosmic scales of $20-150$ Mpc. Notably, the Hubble constant difference $ΔH_0 \approx 0$ is observed at around $85$ Mpc. Despite the smaller sample size ($\sim 10^2$ versus $\sim 10^4$) relative to CF3 at those scales, our analysis show that the Pantheon+ and SH0ES dataset supports the standard model paradigm, which indicates that the Hubble flow becomes statistically uniform at around $70-100$ Mpc, which is compatible with independent determinations of the homogeneity scale based on galaxy number counts.

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arXiv2025

Cosmological constraints from angular homogeneity scale measurements

In this paper, we obtain new measurements of the angular homogeneity scale ($θ_H$) from the BOSS DR12 and eBOSS DR16 catalogs of Luminous Red Galaxies of the Sloan Digital Sky Survey. Considering the flat $Λ$CDM model, we use the $θ_H(z)$ data to constrain the matter density parameter ($Ω_{m0}$) and the Hubble constant ($H_{0}$). We find $H_0 = 65^{+10}_{-7}$ km s$^{-1}$ Mpc$^{-1}$ and $Ω_{m0}>0.296$. By combining the $θ_H$ measurements with current Baryon Acoustic Oscillations (BAO) and Type Ia Supernova (SN) data, we obtain $H_{0}= 66.8 \pm 5.0$ km s$^{-1}$ Mpc$^{-1}$ and $Ω_{m0} = 0.292^{+0.013}_{-0.015}$ ($θ_H$ + BAO) and $H_{0}=66.8 \pm 5.4 $ km s$^{-1}$ Mpc$^{-1}$ and $Ω_{m0}=0.331 \pm 0.018$ ($θ_H$ + SN). We show that $θ_H$ measurements help break the BAO and SN degeneracies concerning $H_0$, as they do not depend on the sound horizon scale at the drag epoch or the SN absolute magnitude value obtained from the distance ladder method. Hence, despite those constraints are less stringent compared to other probes, $θ_H$ data may provide an independent cosmological probe of $H_0$ in light of the Hubble tension. For completeness, we also forecast the constraining power of future $θ_H$ data via Monte Carlo simulations. Considering a relative error of the order of 1$\%$, we obtain competitive constraints on $Ω_{m0}$ and $H_0$ ($\approx 5\%$ error) from the joint analysis with current SN and BAO measurements.

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arXiv2025

Non-parametric reconstructions of cosmic curvature: current constraints and forecasts

The assumption of a flat Universe that follows the cosmological principle, i.e., that the universe is statistically homogeneous and isotropic at large scales, comprises one of the core foundations of the standard cosmological model -- namely, the $Λ$CDM paradigm. Nevertheless, it has been rarely tested in the literature. In this work, we assess the validity of this hypothesis by reconstructing the cosmic curvature with currently available observations, such as Type Ia Supernova and Cosmic Chronometers. We do so by means of null tests, given by consistency relations within the standard model scenario, using a non-parametric method -- which allows us to circumvent prior assumptions on the underlying cosmology. We find no statistically significant departure from the cosmological principle and null curvature in our analysis. In addition, we show that future cosmological observations, specifically those expected from Hubble parameter measurements from redshift surveys, along with gravitational wave observations as standard sirens, will be able to significantly reduce the uncertainties of current reconstructions.

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arXiv2024

Can the angular scale of cosmic homogeneity be used as a cosmological test?

In standard cosmology, the cosmic homogeneity scale is the transition scale above which the patterns arising from non-uniformities -- such as groups and clusters of galaxies, voids, and filaments -- become indistinguishable from a random distribution of sources. Recently, different groups have investigated the feasibility of using such a scale as a cosmological test and arrived at different conclusions. In this paper, we complement and extend these studies by exploring the evolution of the spatial (${\cal{R}}_H$) and angular ($θ_H$) homogeneity scales with redshift, assuming a spatially flat, $Λ$-Cold Dark Matter %($Λ$CDM) universe and linear cosmological perturbation theory. We confirm previous results concerning the non-monotonicity of ${\cal{R}}_H$ with the matter density parameter $Ω_{m0}$ but also show that it exhibits a monotonical behavior with the Hubble constant $H_0$ within a large redshift interval. More importantly, we find that, for $z \gtrsim 0.6$, the angular homogeneity scale not only presents a monotonical behavior with $Ω_{m0}$ and $H_0$ but is quite sensitive to $H_0$, especially at higher redshifts. These results, therefore, raise the possibility of using $θ_H$ as a new, model-independent way to constrain cosmological parameters.

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arXiv2024

Testing the isotropy of cosmic acceleration with Pantheon+ and SH0ES: A cosmographic analysis

We use a recent Pantheon+SH0ES compilation of Type Ia Supernova distance measurements at low-redshift, i.e., $0.01 \leq z \leq 0.10$, in order to investigate the directional dependency of the deceleration parameter ($q_0$) in different patches ($60^{\circ}$ size) across the sky, as a probe of the statistical isotropy of the Universe. We adopt a cosmographic approach to compute the cosmological distances, fixing $H_0$ and $M_B$ to reference values provided by the collaboration. By looking at 500 different patches randomly taken across the sky, we find a maximum $\sim 3σ$ CL anisotropy level for $q_0$, whose direction points orthogonally to the cosmic microwave background (CMB) dipole axis, i.e., $(RA^{\rm SN},DEC^{\rm SN}) = (267^{\circ},6^{\circ})$ vs $(RA^{\rm CMB},DEC^{\rm CMB}) = (167^{\circ},-7^{\circ})$. We assessed the statistical significance of those results, finding that such a signal is expected due to the limitations of the observational sample. These results support that there is no significant evidence for a departure from the cosmic isotropy assumption, one of the pillars of the standard cosmological model.

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arXiv2022

The angular scale of homogeneity with SDSS-IV DR16 Luminous Red Galaxies

We report measurements of the angular scale of cosmic homogeneity ($θ_{H}$) using the recently released luminous red galaxy sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV LRG DR16). It consists of a model-independent method, as we only use the celestial coordinates of these objects to carry out such an analysis. The observational data is divided into thin redshift bins, namely $0.67<z<0.68$, $0.70<z<0.71$, and $0.73<z<0.74$, in order to avoid projection biases, and we estimate our uncertainties through a bootstrap method and a suite of mock catalogues. We find that the LRGs exhibit an angular scale of homogeneity consistent with the predictions of the standard cosmology within the redshift interval studied. Considering the bootstrap method, in which the measurements are obtained in a model-independent way, we found at 1$σ$ level that $θ_H^{boot}(0.675) = 7.57 \pm 2.91$ deg, $θ_H^{boot} (0.705) = 7.49 \pm 2.63$ deg and $θ_H^{boot} (0.735) = 8.88 \pm 2.81$ deg. Such results are in good agreement with the ones obtained using mock catalogues built under the assumption of the standard cosmological model.

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arXiv2021

Null tests of the concordance model in the era of Euclid and the SKA

We perform null tests of the concordance model, using $H(z)$ measurements that mimic next-generation surveys such as Euclid and the SKA. To this end, we deploy a non-parametric method, so that we make minimal assumptions about the fiducial cosmology as well as the statistical analysis. We produce simulations assuming different cosmological models in order to verify how well we can distinguish between their signatures. We find that SKA- and Euclid-like surveys should be able to discriminate sharply between the concordance and alternative dark energy models that are compatible with the Planck CMB data. We conclude that SKA and Euclid will be able to falsify the concordance model in a statistically significant way, if one of the benchmarks models represents the true Universe, without making assumptions about the underlying cosmology.

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arXiv2021

Measuring the cosmic homogeneity scale with SDSS-IV DR16 Quasars

We report measurements of the scale of cosmic homogeneity ($r_{h}$) using the recently released quasar sample of the sixteenth data release of the Sloan Digital Sky Survey (SDSS-IV DR16). We perform our analysis in 2 redshift bins lying in the redshift interval $2.2 < z < 3.2$ by means of the fractal dimension $D_2$. By adopting the usual assumption that $r_{h}$ is obtained when $D_2 \sim 2.97$, that is, within 1% of $D_2=3$, we find the cosmic homogeneity scale with a decreasing trend with redshift, and in good agreement with the $Λ$CDM prediction. Our results confirm the presence of a homogeneity scale in the spatial distribution of quasars as predicted by the fundamental assumptions of the standard cosmological model.

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arXiv2020

Is there evidence for a hotter Universe?

The measurement of present-day temperature of the Cosmic Microwave Background (CMB), $T_0 = 2.72548 \pm 0.00057$ K (1$σ$), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, $H_0$, obtained from measurements of the CMB temperature fluctuations assuming the standard $Λ$CDM model exhibit a large ($4.1σ$) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in $T_0$ could alleviate or solve the $H_0$-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift $T(z)$ measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of $\gtrsim 1.9σ$ from the $T_0$ values required to solve the $H_0$ tension. This result reinforces the idea that a solution of the $H_0$-tension problem in fact requires either a better understanding of the systematic errors on the $H_0$ measurements or new physics.

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arXiv2020

Is there any measurable redshift dependence on the SN Ia absolute magnitude?

We test the cosmological implications of a varying absolute magnitude of Type Ia supernovae using the Pantheon compilation, by reconstructing different phenomenological approaches that could justify a varying absolute magnitude, but also approaches based on cosmic voids, modified gravity models and a binning scheme. In all the cases considered in this work, we find good agreement with the expected values of the standard $Λ$CDM model and no evidence of new physics.

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arXiv2020

The Hubble constant tension with next-generation galaxy surveys

The rate at which the universe is expanding today is a fundamental parameter in cosmology which governs our understanding of structure formation and dark energy. However, current measurements of the Hubble constant, $H_0$, show a significant tension ($\sim 4-6σ$) between early- and late-Universe observations. There are ongoing efforts to check the diverse observational results and also to investigate possible theoretical ways to resolve the tension~-- which could point to radical extensions of the standard model. Here we demonstrate the potential of next-generation spectroscopic galaxy surveys to shed light on the Hubble constant tension. Surveys such as those with Euclid and the Square Kilometre Array (SKA) are expected to reach sub-percent precision on Baryon Acoustic Oscillation (BAO) measurements of the Hubble parameter, with a combined redshift coverage of $0.1<z<3$. This wide redshift range, together with the high precision and low level of systematics in BAO measurements, mean that these surveys will provide independent and tight constraints on $H(z)$. These $H(z)$ measurements can be extrapolated to $z = 0$ to provide constraints on $H_0$ using a non-parametric regression. To this end we deploy Gaussian processes and we find that Euclid-like surveys can reach $\sim$3\% precision on $H_0$, with SKA-like intensity mapping surveys reaching $\sim$2\%. When we combine the low-redshift SKA-like Band 2 survey with either its high-redshift Band 1 counterpart, or with the non-overlapping Euclid-like survey, the precision is predicted to be close to 1\% with 40 $H(z)$ data points. This would be sufficient to rule out the current early- or late-Universe measurements at a $\sim$5$σ$ level.

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arXiv2020

Evidence for cosmic acceleration with next-generation surveys: A model-independent approach

We quantify the evidence for cosmic acceleration using simulations of $H(z)$ measurements from SKA- and Euclid-like surveys. We perform a non-parametric reconstruction of the Hubble parameters and its derivative to obtain the deceleration parameter $q(z)$ using the Gaussian Processes method. This is a completely model-independent approach, so we can determine whether the Universe is undergoing accelerated expansion {\it regardless} of any assumption of a dark energy model. We find that Euclid-like and SKA-like band 1 surveys can probe cosmic acceleration at over $3$ and $5σ$ confidence level, respectively. By combining them with a SKA-like band 2 survey, which reaches lower redshift ranges, the evidence for a current accelerated phase increases to over $7σ$. This is a significant improvement from current $H(z)$ measurements from cosmic chronometers and galaxy redshift surveys, showing that these surveys can underpin cosmic acceleration in a model-independent way.

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