arXiv subjects

Arianna Favale

Publications and source records attributed to Arianna Favale.

8 recordsLinked to original sources

arXiv2025

Revisiting model-independent constraints on spatial curvature and cosmic ladders calibration: updated and forecast analyses

Model-independent approaches have gained increasing attention as powerful tools to investigate persistent tensions between cosmological observations and the predictions of $\Lambda$CDM. Notably, recent DESY5 Type Ia Supernovae (SNIa) and DESI Baryon Acoustic Oscillation (BAO) data challenge the validity of the cosmological constant, and they remain in tension with SH0ES local distance ladder measurements under standard pre-recombination physics. Building on our previous work, MNRAS 523 (2023) 3, 3406-3422, we present a follow-up analysis of the model-independent calibration of the local and inverse distance ladders using cosmic chronometers (CCH) data and Gaussian Processes. We jointly constrain the SNIa absolute magnitude, $M$, the comoving sound horizon at the baryon-drag epoch, $r_d$, and the spatial curvature parameter, $\Omega_k$, using CCH with DESY5 and DESI DR1/DR2. We find this data combination compatible with a flat universe at $\sim1.7\sigma$, with $\Omega_k=-0.143\pm0.085$, showing weaker compatibility than with Pantheon+, while the ladder calibrators read $M=-19.324_{-0.095}^{+0.092}$ and $r_d=(144.00^{+5.38}_{-4.88}$) Mpc. Although current uncertainties limit the precision of our constraints and prevent us from arbitrating the Hubble tension, it is nevertheless instructive to explore the constraining power of our methodology with future SNIa, CCH, and BAO from surveys such as LSST, Euclid, and DESI. We present the first forecast analysis for the triad $(M,\Omega_k,r_d)$, finding that, in an optimistic scenario, upcoming data will improve agnostic constraints on $M$ by $\sim$54% and on $r_d$ by $\sim$66%, enabling a $\sim2$% determination of $H_0$. Precision on $\Omega_k$ will increase by $\sim50$%. Our analysis outlines which improvements in future data - whether in quality, quantity, or redshift coverage - are likely to most effectively tighten these constraints.[abridged]

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arXiv2025

Revisiting Gaussian Process Reconstruction for Cosmological Inference: The Generalised GP (Gen GP) Framework

We investigate uncertainties in the estimation of the Hubble constant ($H_0$) arising from Gaussian Process (GP) reconstruction, demonstrating that the choice of kernel introduces systematic variations comparable to those arising from different cosmological models. To address this limitation, we introduce the Generalized Gaussian Process (Gen GP) framework, in which the Mat\'ern smoothness parameter $\nu$ is treated as a free parameter, allowing for data-driven kernel optimization. Using the cosmic chronometer Hubble data, we find that while standard GP with $\Lambda$CDM mean function exhibits noticeable reconstruction differences between optimized and marginalized approaches, particularly at $z > 1$, Gen GP maintains methodological consistency. In Gen GP, slight increases in $\chi^2$ per degree of freedom relative to standard GP, for both the zero-mean and $\Lambda$CDM prior mean cases, reflect added flexibility rather than performance degradation. Our results emphasize that robust cosmological inference requires treating kernel parameters as free variables and implementing full Bayesian marginalization to avoid artificial precision from fixed hyperparameters. As machine learning becomes central to cosmological discovery, the Gen GP framework provides a principled approach to model-independent inference that properly accounts for methodological uncertainties while maintaining necessary flexibility for reliable parameter estimation.

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arXiv2025

Illustrating the consequences of a misuse of $\sigma_8$ in cosmology

The parameter $\sigma_8$ is the rms mass fluctuations on a scale of $R_8=8h^{-1}$ Mpc and is used to quantify the amplitude of matter fluctuations at linear scales. However, the dependence of $R_8$ on $h$ complicates direct comparisons of $\sigma_8$ values obtained under different assumptions about $H_0$, since $\sigma_8$ in such cases characterizes the amount of structure at different physical scales. This issue arises both when comparing $\sigma_8$ values from fitting analyses of cosmological models with differing $H_0$ posteriors, and when contrasting constraints from galaxy clustering experiments with different priors on $H_0$. As first noted by Ariel G. S\'anchez in PRD 102, 123511 (2020), quantifying the growth tension using $\sigma_8$ can introduce substantial biases and couple the growth and Hubble tensions in an intricate way. To address these challenges, S\'anchez proposed an alternative parameter, $\sigma_{12}$, defined as the rms mass fluctuations at $12$ Mpc, which is independent of $h$. Although S\'anchez's work was published five years ago and other authors have since highlighted the limitations of $\sigma_8$, much of the cosmological community -- including large collaborations -- continues to rely on this parameter rather than adopting $\sigma_{12}$, seemingly due only to historical considerations. In this work, we illustrate the biases introduced by $\sigma_8$ through some clear examples, aiming to motivate the community to transition from $\sigma_8$ to $\sigma_{12}$. We show that the bias found in models with large values of $H_0$ is more prominent, artificially complicating the search for a model that can efficiently resolve the Hubble tension without exacerbating the growth tension inferred from galaxy clustering measurements. We argue that the worsening of the growth tension in these models is much less pronounced than previously thought or may even be nonexistent.

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arXiv2024

Quantification of 2D vs 3D BAO tension using SNIa as a redshift interpolator and test of the Etherington relation

Several studies in the literature have found a disagreement between data on Baryon Acoustic Oscillations (BAO) derived using two distinct methodologies: the two-dimensional (2D or angular) BAO, which extracts the BAO signal from the angular two-point correlation function; and the three-dimensional (3D) BAO, which also exploits the radial signal imprinted on the large-scale structure of the universe. This discrepancy is worrisome, since many of the points contained in these data sets are obtained from the same catalogs of tracers, so we would expect them to be consistent. Since BAO measurements play a pivotal role in the building of the inverse distance ladder, this mismatch impacts the discourse on the Hubble tension and the theoretical solutions to the latter. So far, the discrepancy between 2D and 3D BAO has been only pointed out in the context of fitting analyses of cosmological models or parametrizations that involve a concrete calibration of the comoving sound horizon at the baryon-drag epoch. In this Letter, we avoid the use of any calibration and cosmological model, assuming that the Etherington (a.k.a distance duality) relation holds. We use state-of-the-art measurements in our analysis, and study how the results change when the angular components of the 3D BAO data from BOSS/eBOSS are substituted by the recent data from DESI Y1. We find the tension to exist at the level of $\sim 2σ$ and $\sim 2.5σ$, respectively, when the SNIa of Pantheon+ are used, and at $\sim 4.6σ$ when they are replaced with those of DES Y5. We then apply a calibrator-independent method to investigate the robustness of the distance duality relation when analyzed not only with 3D BAO measurements, but also with 2D BAO. We do not find any hint for a violation of the cosmic distance duality relation in any of the considered data sets. [abridged]

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arXiv2024

A model-independent treatment of cosmic ladder calibration and $Ω_k$ measurement through low-$z$ observations

Looking at the well-known Hubble tension as a tension in the calibrators of the cosmic distance ladder, i.e. the absolute magnitude $M$ of standard candles such as supernovae of Type Ia (SNIa) and the standard ruler represented by the comoving sound horizon at the baryon-drag epoch, $r_d$, we propose a model-independent method to measure these distance calibrators independently from the cosmic microwave background and the first rungs of the direct distance ladder. To do so, we leverage state-of-the-art data on cosmic chronometers (CCH), SNIa and baryon acoustic oscillations (BAO) from various galaxy surveys. Taking advantage of the Gaussian Processes Bayesian technique, we reconstruct $M(z)$, $Ω_k(z)$ and $r_d(z)$ at $z\lesssim2$ and check that no significant statistical evolution is preferred at 68\% C.L. This allows us to treat them as constants and constrain them assuming the metric description of gravity, the cosmological principle and the validity of CCH as reliable cosmic clocks, and SNIa and BAO as optimal standard candles and standard rulers, respectively, but otherwise in a model-independent way. We obtain: $Ω_k=-0.07^{+0.12}_{-0.15}$, $M=(-19.314^{+0.086}_{-0.108})$ mag and $r_d=(142.3\pm 5.3)$ Mpc. At present, the uncertainties derived are still too large to arbitrate the tension but this is bound to change in the near future with the advent of upcoming surveys and data.

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arXiv2024

Towards a new model-independent calibration of Gamma-Ray Bursts

Current data on baryon acoustic oscillations and Supernovae of Type Ia cover up to $z\sim 2.5$. These observations play a very important role in the determination of cosmological parameters and have been widely used to constrain the $\Lambda$CDM and models beyond it. To extend the investigation to higher $z$, Gamma-Ray Bursts (GRBs) stand out as one of the most promising observables since can probe the universe up to $z\sim9.4$. The use of GRB correlations is still a challenge due to the spread in their intrinsic properties. In this work, we propose an innovative and cosmology-independent method of calibration of the so-called 3D Dainotti correlation. We employ state-of-the-art data on Cosmic Chronometers (CCH) at $z\lesssim2$ and use the Gaussian Processes reconstruction tool. To match the CCH redshift range, we select 20 long GRBs in $0.553\leq z\leq1.96$ from the Platinum sample, which consists of well-defined GRB plateau properties that obey the fundamental plane relation. We verify that the choice of priors on the parameters of the Dainotti relation and the modelling of CCH uncertainties and covariance have negligible impact on our results. We also consider the case in which the redshift evolution of the physical features of the plane is accounted for. We find that the use of CCH allows us to identify a sub-sample of GRBs that adhere even more closely to the fundamental plane relation, with an intrinsic scatter of $\sigma_{int}=0.20^{+0.03}_{-0.05}$ when evolutionary effects are considered. In an epoch in which we strive to reduce uncertainties on the GRB correlations variables to tighten constraints on cosmological parameters, we have found a novel model-independent approach to pinpoint a sub-sample that can thus represent a valuable set of standardizable candles. This allows us to extend the distance ladder presenting a new catalogue of calibrated luminosity distances up to $z=5$.

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arXiv2023

Late-time phenomenology required to solve the $H_0$ tension in view of the cosmic ladders and the anisotropic and angular BAO data sets

The $\sim 5σ$ mismatch between the value of the Hubble parameter measured by SH0ES and the one inferred from the inverse distance ladder (IDL) constitutes the biggest tension afflicting the standard model of cosmology, which could be pointing to the need of physics beyond $Λ$CDM. In this paper we study the background history required to solve the $H_0$ tension if we consider standard prerecombination physics, paying special attention to the role played by the data on baryon acoustic oscillations (BAO) employed to build the IDL. We show that the anisotropic BAO data favor an ultra-late-time (phantom-like) enhancement of $H(z)$ at $z\lesssim 0.2$, accompanied by a transition in the absolute magnitude of supernovae of Type Ia $M(z)$ in the same redshift range. This agrees with previous findings in the literature. The effective dark energy (DE) density must be smaller than in the standard model at higher redshifts. Instead, when angular BAO data (claimed to be less subject to model dependencies) is employed in the analysis, we find that the increase of $H(z)$ starts at much higher redshifts, typically in the range $z\sim 0.5-0.8$. In this case, $M(z)$ could experience also a transition (although much smoother) and the effective DE density becomes negative at $z\gtrsim 2$. Both scenarios require a violation of the weak energy condition (WEC), but leave an imprint on completely different redshift ranges and might also have a different impact on the perturbed observables. They allow for the effective crossing of the phantom divide. Finally, we employ two alternative methods to show that current data from cosmic chronometers do not exclude the violation of the WEC, but do not add any strong evidence in its favor neither. Our work puts the accent on the utmost importance of the choice of the BAO data set in the study of the possible solutions to the $H_0$ tension.

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arXiv2023

Cosmic chronometers to calibrate the ladders and measure the curvature of the Universe. A model-independent study

We use the state-of-the-art data on cosmic chronometers (CCH) and the Pantheon+ compilation of supernovae of Type Ia (SNIa) to test the constancy of the SNIa absolute magnitude, $M$, and the robustness of the cosmological principle (CP) at $z\lesssim 2$ with a model-agnostic approach. We do so by reconstructing $M(z)$ and the curvature parameter $Ω_{k}(z)$ using Gaussian Processes. Moreover, we use CCH in combination with data on baryon acoustic oscillations (BAO) from various galaxy surveys (6dFGS, BOSS, eBOSS, WiggleZ, DES Y3) to measure the sound horizon at the baryon-drag epoch, $r_d$, from each BAO data point and check their consistency. Given the precision allowed by the CCH, we find that $M(z)$, $Ω_k(z)$ and $r_d(z)$ are fully compatible (at $<68\%$ C.L.) with constant values. This justifies our final analyses, in which we put constraints on these constant parameters under the validity of the CP, the metric description of gravity and standard physics in the vicinity of the stellar objects, but otherwise in a model-independent way. If we exclude the SNIa contained in the host galaxies employed by SH0ES, our results read $M=(-19.314^{+0.086}_{-0.108})$ mag, $r_d=(142.3\pm 5.3)$ Mpc and $Ω_k=-0.07^{+0.12}_{-0.15}$, with $H_0=(71.5\pm 3.1)$ km/s/Mpc ($68\%$ C.L.). These values are independent from the main data sets involved in the $H_0$ tension, namely, the cosmic microwave background and the first two rungs of the cosmic distance ladder. If, instead, we also consider the SNIa in the host galaxies, calibrated with Cepheids, we measure $M=(-19.252^{+0.024}_{-0.036})$ mag, $r_d=(141.9^{+5.6}_{-4.9})$ Mpc, $Ω_k=-0.10^{+0.12}_{-0.15}$ and $H_0=(74.0^{+0.9}_{-1.0})$ km/s/Mpc.

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