arXiv subjects

Susana J. Landau

Publications and source records attributed to Susana J. Landau.

At least 19 recordsLinked to original sources

arXiv2026

Observational constraints on Luciano-Saridakis holographic dark energy

Holographic dark energy (HDE) models provide a natural framework for linking gravitational thermodynamics to the late-time accelerated expansion of the Universe. In this work, we investigate the observational viability of an extended HDE scenario arising from a recently proposed generalized entropy. For bounded systems, this entropy exhibits a generalized holographic scaling with two independent area contributions, giving rise to a modified HDE density that encompasses both standard HDE and $Λ$CDM as limiting cases. Focusing on the Hubble-horizon infrared cutoff, we constrain the model using Cosmic Chronometers, the Pantheon$^+$+SH0ES Type Ia supernova compilation, DESI DR2 baryon acoustic oscillations, and compressed Planck 2018 CMB shift parameters. We find that the model provides an excellent fit to the combined dataset and admits regions of parameter space in which the Pantheon$^+$+SH0ES and CMB constraints can be simultaneously accommodated. The preferred solutions lie close to the $Λ$CDM regime, although non-standard entropic contributions remain compatible with current observations. We further compare the complete realization of the model, containing both independent area contributions, with its reduced single-contribution limit, finding that both provide essentially equivalent descriptions of the data, with a mild preference for the latter. Our results establish generalized entropic HDE as a viable and theoretically motivated extension of the standard cosmological scenario and provide the first observational assessment of this cosmological framework.

physics.gen-ph↗

arXiv2026

Hubble tension and small-scale inhomogeneities on light propagation

Context. A major observational challenge within the standard cosmological framework is the Hubble tension, a statistically significant ($\sim 5σ$) disagreement between the Hubble constant derived from cosmic microwave background measurements and the value obtained through local distance-ladder methods based on Type Ia supernovae and Cepheid variable stars. Aims. We relax the assumption of the Friedmann-Lemaître-Robertson-Walker (FLRW) distance-redshift relation and explore the influence of small-scale inhomogeneities on the propagation of light from distant sources, using the Zeldovich-Kantowski-Dyer-Roeder (ZKDR) approximation as an alternative approach to address this tension. Methods. We employ two distinct formulations of the ZKDR equation to test our hypothesis using recent Type Ia supernovae datafrom the Pantheon+ compilation and the SH0ES collaboration and six gravitational lens systems from the H0LiCOW collaboration. Results. We obtained constraints on the cosmological parameters and the ZKDR model parameters within the framework of the inhomogeneous models considered. The model comparison criterion indicates that the data show weak preference of $Λ$CDM over the flat ZKDR model , whereas the remaining models studied are strongly disfavored. Conclusions. Our findings indicate that a background model characterized by the ZKDR approximation and its modifications does not solve or alleviate the Hubble tension.

astro-ph.CO↗

arXiv2026

Observational constraints on Luciano-Saridakis entropic cosmology

A recently proposed generalized entropy by Luciano and Saridakis extends the standard Boltzmann-Gibbs and Bekenstein-Hawking framework through a microscopically motivated construction involving two independent entropic exponents. When applied within the gravity-thermodynamics correspondence, this entropy leads to a modified cosmological dynamics that can be interpreted as an effective dark energy sector of entropic origin, while recovering $Λ$CDM in appropriate limits. In this work, we perform the first observational confrontation of the resulting entropic cosmology at the background level. Focusing on the case $α_δ=0$, we constrain the model using Cosmic Chronometers, Pantheon$^+$ Type Ia supernovae calibrated with SH0ES, BAO measurements from DESI DR2 and compressed Planck 2018 CMB information. We find that the model yields a statistically robust fit to the combined data sets and can simultaneously satisfy Pantheon$^+$, SH0ES and CMB shift-parameter constraints, unlike $Λ$CDM. Although the entropic parameters remain close to their standard values, the $Λ$CDM limit is excluded at the $2σ$ level within the restricted parameter space considered. These results indicate that the Luciano-Saridakis entropic cosmology offers a viable extension of the standard model with the potential to alleviate the Hubble tension at the background level.

astro-ph.CO↗

arXiv2026

Geometric Cosmology models: statistical analysis with observational data

Although the standard cosmological model is capable of explaining most current observational data, it faces some theoretical and observational issues. This is the main motivation for exploring alternative cosmological models. In this paper, we focus on a novel proposal that consists in adding an infinite tower of higher-order curvature invariants to the usual Einstein-Hilbert action. We obtain the late-time background evolution for three families of models that can be obtained from this proposal. We use recent data from Cosmic Chronometers and type Ia supernovae to test the late-time predictions of our models. In addition, we consider estimations from the Age of the Older Globular Clusters to constrain our models. While some of the studied cases are ruled out by the data, we show that there are particular cases of the GILA model that can explain current data.

astro-ph.CO↗

arXiv2025

Generalized tension metrics for multiple cosmological datasets

We introduce a novel estimator to quantify statistical tensions among multiple cosmological datasets simultaneously. This estimator generalizes the Difference-in-Means statistic, $Q_{\rm DM}$, to the multi-dataset regime. Our framework enables the detection of dominant tension directions in the shared parameter space. It further provides a geometric interpretation of the tension for the two- and three-dataset cases in two dimensions. According to this approach, the previously reported increase in tension between DESI and Planck from $1.9σ$ (DR1) to $2.3σ$(DR2) is reinterpreted as a more modest shift from $1.18σ^{\rm eff}$ (DR1) to $1.45σ^{\rm eff}$ (DR2). These new tools may also prove valuable across research fields where dataset discrepancies arise.

astro-ph.CO↗

arXiv2025

Evolution of linear matter perturbations with error-bounded bundle physics-informed neural networks

We consider the evolution of linear matter perturbations in the context of the standard cosmological model ($Λ$CDM) and a phenomenological modified gravity model. We use the physics-informed neural network (PINN) bundle method, which allows to integrate differential systems as an alternative to the traditional numerical method. We apply the PINN bundle method to the equation that describes the matter perturbation evolution, to compare its outcomes with recent data on structure growth, $fσ_8$. Unlike our previous works, we can calculate a bound on the error of this observable without using the numerical solution of the equation. For this, we use a method developed previously by ourselves to calculate an exact bound on the PINN-based solution using only the outcomes of the network and its residual. On the other hand, the use of an updated data set allows us to obtain more stringent constraints on the plane $Ω_m-σ_8$ than previous works.

astro-ph.CO↗

arXiv2025

The frozen vanilla model: Exploring dark sector interactions with delta effective theories

In this paper, we introduce a new interacting mechanism within the dark sector, encompassing both dark energy and dark matter, while grounding our analysis in the familiar framework of the $\mathrm{ΛCDM}$ model augmented by baryons and radiation components, including photons and neutrinos. The interaction between dark energy and dark matter is confined to the perturbative level. One significant advantage of this proposal is that all geometric probes yield constraints consistent with the so-called vanilla model or the extended vanilla model, where dark energy has a constant equation of state, $w_{x}$. However, the introduction of this new interacting mechanism affects several theoretical signatures, involving contrast dark matter and dark energy densities. We perform an exploratory analysis of those effects in the CMB power spectra, matter-power spectra, and redshift space distortions. For instance, it allows for a decrease/increment in the integrated Sachs-Wolfe (ISW) effect depending on the value taken by the interaction coupling. This effect could be observationally detected by looking for a cross-correlation between the ISW temperature fluctuations and the distribution of galaxies or quasars. At late times, the interaction in the dark sector becomes very effective, affecting the non-linear scale of structure formation. We discuss how the estimators $fσ_{8}(z)$ and $S_{8}(z)$ are affected by different interacting couplings; indicating that $fσ_{8}(z)$ can show a relative change of up to $15\%$ compared to the concordance model at low redshifts. Finally, we show how the various terms in the dark energy pressure perturbation (both adiabatic and non-adiabatic) are relevant for different scales, demonstrating the absence of large-scale instabilities.

gr-qc↗

arXiv2025

On Geometric Cosmology

We present a modification to General Relativity by making a redefinition of the coupling constant in front of the Ricci curvature scalar along with the Generalized Quasi-topological Gravity theories added to the action, that we named Geometric Cosmology. We give four different exponential convergent models for this class of theories belonging to three different gravities of the Geometric Cosmology theories.

gr-qc↗

arXiv2024

Exact and approximate error bounds for physics-informed neural networks

The use of neural networks to solve differential equations, as an alternative to traditional numerical solvers, has increased recently. However, error bounds for the obtained solutions have only been developed for certain equations. In this work, we report important progress in calculating error bounds of physics-informed neural networks (PINNs) solutions of nonlinear first-order ODEs. We give a general expression that describes the error of the solution that the PINN-based method provides for a nonlinear first-order ODE. In addition, we propose a technique to calculate an approximate bound for the general case and an exact bound for a particular case. The error bounds are computed using only the residual information and the equation structure. We apply the proposed methods to particular cases and show that they can successfully provide error bounds without relying on the numerical solution.

cs.LG↗

arXiv2024

Tensions in cosmology: a discussion of statistical tools to determine inconsistencies

We present a comprehensive analysis of statistical tools for evaluating tensions in cosmological parameter estimates arising from distinct datasets. Focusing on the unresolved Hubble constant ($H_0$) tension, we explore the Pantheon Plus + SH0ES (PPS) compilation, which includes low-redshift Cepheid data from the SH0ES collaboration, along with the latest release of CMB data from the Planck collaboration, Cosmic Chronometers (CC) dataset and the most recent Baryonic Acoustic Oscillation (BAO) datasets. Employing various tension metrics, we quantitatively assess the inconsistencies in parameter estimates, emphasizing the importance of capturing multidimensional tensions. Our results reveal substantial tension between PPS and Planck 2018 datasets and moderate tension between the BAO data sets and all other datasets. We highlight the importance of adopting these metrics to enhance the precision of future cosmological analyses and facilitate the resolution of existing tensions.

astro-ph.CO↗

arXiv2024

Faster Bayesian inference with neural network bundles and new results for $f(R)$ models

In the last few years, there has been significant progress in the development of machine learning methods tailored to astrophysics and cosmology. We have recently applied one of these, namely, the neural network bundle method, to the cosmological scenario. Moreover, we showed that in some cases the computational times of the Bayesian inference process can be reduced. In this paper, we present an improvement to the neural network bundle method that results in a significant reduction of the computational times of the statistical analysis. The novel aspect consists of the use of the neural network bundle method to calculate the luminosity distance of type Ia supernovae, which is usually computed through an integral with numerical methods. In this work, we have applied this improvement to the Hu-Sawicki and Starobinsky $f(R)$ models. We also performed a statistical analysis with data from type Ia supernovae of the Pantheon+ compilation and cosmic chronometers. Another original aspect of this work is the different treatment we provide for the absolute magnitude of type Ia supernovae during the inference process, which results in different estimates of the distortion parameter than the ones obtained in the literature. We show that the statistical analyses carried out with our new method require lower computational times than the ones performed with both the numerical and the neural network method from our previous work. This reduction in time is more significant in the case of a difficult computational problem such as the ones addressed in this work.

astro-ph.CO↗

arXiv2023

Cosmology-informed neural networks to solve the background dynamics of the Universe

The field of machine learning has drawn increasing interest from various other fields due to the success of its methods at solving a plethora of different problems. An application of these has been to train artificial neural networks to solve differential equations without the need of a numerical solver. This particular application offers an alternative to conventional numerical methods, with advantages such as lower memory required to store solutions, parallelization, and, in some cases, a lower overall computational cost than its numerical counterparts. In this work, we train artificial neural networks to represent a bundle of solutions of the differential equations that govern the background dynamics of the Universe for four different models. The models we have chosen are $Λ\mathrm{CDM}$, the Chevallier-Polarski-Linder parametric dark energy model, a quintessence model with an exponential potential, and the Hu-Sawicki $f(R)$ model. We use the solutions that the networks provide to perform statistical analyses to estimate the values of each model's parameters with observational data; namely, estimates of the Hubble parameter from cosmic chronometers, type Ia supernovae data from the Pantheon compilation, and measurements from baryon acoustic oscillations. The results we obtain for all models match similar estimations done in the literature using numerical solvers. In addition, we estimate the error of the solutions that the trained networks provide by comparing them with the analytical solution when there is one, or to a high-precision numerical solution when there is not. Through these estimations we find that the error of the solutions is at most $\sim1\%$ in the region of the parameter space that concerns the $95\%$ confidence regions that we find using the data, for all models and all statistical analyses performed in this work.

astro-ph.CO↗

arXiv2022

Cosmological constraints on unimodular gravity models with diffusion

A discrete space-time structure lying at about the Planck scale may become manifest in the form of very small violations of the conservation of the matter energy-momentum tensor. In order to include such kind of violations, forbidden within the General Relativity framework, the theory of unimodular gravity seems as the simplest option to describe the gravitational interaction. In the cosmological context, a direct consequence of such violation of energy conservation might be heuristically viewed a "diffusion process of matter (both dark and ordinary)" into an effective dark energy term in Einstein's equations, which leads under natural assumptions to an adequate estimate for the value of the cosmological constant. Previous works have also indicated that these kind of models might offer a natural scenario to alleviate the Hubble tension. In this work, we consider a simple model for thecosmological history including a late time occurrence of such energy violation and study the modifications of the predictions for the anisotropy and polarization of the Cosmic Microwave Background (CMB). We compare the model's predictions with recent data from the CMB, Supernovae Type Ia, cosmic chronometers and Baryon Acoustic Oscillations. The results show the potential of this type of model to alleviate the Hubble tension.

astro-ph.CO↗

arXiv2022

Testing f(R) gravity models with quasar X-ray and UV fluxes

Recently, Active Galactic Nuclei (AGNs) have been proposed as standardizable candles, thanks to an observed non-linear relation between their X-ray and optical-ultraviolet (UV) luminosities, which provides an independent measurement of their distances. In this paper, we use these observables for the first time to estimate the parameters of f(R) gravity models (specifically the Hu-Sawicki and the exponential models) together with the cosmological parameters. The importance of this type of modified gravity theories lies in the fact that they can explain the late time accelerated expansion of the universe without the inclusion of a dark energy component. We have also included other observable data to the analyses such as estimates of the Hubble parameter H(z) from Cosmic Chronometers, the Pantheon Type Ia supernovae compilation, and Baryon Acoustic Oscillations measurements. Our results show that the allowed space parameter is restricted when both AGN and BAO data are added to CC and SnIa data, being the BAO data set the most restrictive one. We can also conclude that even though our results are consistent with the ones from the LCDM model, small deviations from General Relativity, than can be successfully described by the f(R) models studied in this paper, are also allowed by the considered data sets.

astro-ph.CO↗

arXiv2020

Testing Modified Gravity theory (MOG) with Type Ia Supernovae, Cosmic Chronometers and Baryon Acoustic Oscillations

We analyse the MOdified Gravity (MOG) theory, proposed by Moffat, in a cosmological context. We use data from Type Ia Supernovae (SNe Ia), Baryon Acoustic Oscillations (BAO) and Cosmic Chronometers (CC) to test MOG predictions. For this, we perform $χ^2$ tests considering fixed values of $H_0$ and $V_G$, the self-interaction potential of one of the scalar fields in the theory. Our results show that the MOG theory is in agreement with all data sets for some particular values of $H_0$ and $V_G$, being the BAO data set the most powerful tool to test MOG predictions, due to its constraining power.

astro-ph.CO↗

arXiv2020

Solar System tests and chameleon effect in f (R) gravity

Using a novel and self-consistent approach that avoids the scalar-tensor identification in the Einstein frame, we reanalyze the viability of f(R) gravity within the context of solar-system tests. In order to do so, we depart from a simple but fully relativistic system of differential equations that describe a compact object in a static and spherically symmetric spacetime, and then we make suitable linearizations that apply to nonrelativistic objects such as the Sun. We then show clearly under which conditions the emerging chameleonlike mechanism can lead to a post-Newtonian parameter γ compatible with the observational bounds. To illustrate this method, we use several specific f(R) models proposed to explain the current acceleration of the Universe, and we show which of them are able to satisfy those bounds.

gr-qc↗

arXiv2020

Variation of fundamental constants and white dwarfs

Theories that attempt to unify the four fundamental interactions and alternative theories of gravity predict time and/or spatial variation of the fundamental constants of nature. Different versions of these theories predict different behaviours for these variations. In consequence, experimental and observational bounds are an important tool to check the validity of such proposals. In this paper, we review constraints on the possible variation of the fundamental constants from astronomical observations and geophysical experiments designed to test the constancy of the fundamental constants of nature over different timescales. We also focus on the limits that can be obtained from white dwarfs, which can constrain the variation of the constants with the gravitational potential.

astro-ph.CO↗

arXiv2019

Thick shell regime in the chameleon two-body problem

In a previous paper [Phys. Rev. D 97, 104044 (2018)] we pointed out some shortcomings of the standard approach to chameleon theories consisting in treating the small bodies used to test the weak equivalence principle (WEP) as test particles, whose presence do not modify the chameleon field configuration. In that paper we developed an alternative method to determine the relevant field configuration which takes into account the influence of both test and source bodies, and computed the chamaleon mediated force. Relying on that analysis we showed that the effective acceleration of test bodies is composition dependent even when the model is based on universal couplings. In this paper, we improve our method by using a more suitable approximation for the effective chameleon potential in situations where the bodies are in the so-called "thick shell regime". We then find new and more restrictive bounds on the model' s parametres by confronting the new theoretical predictions with the empirical bounds on Eötvös parameter comming from the lunar laser ranging experiments.

gr-qc↗