V Joint ICTP-Trieste/ICTP-SAIFR School on Cosmology

Previous events:

IV Joint ICTP-Trieste/ICTP-SAIFR School on Cosmology: Challenges for the Standard Cosmological Model

III Joint ICTP-Trieste/ICTP-SAIFR School on Observational Cosmology

II Joint ICTP-Trieste/ICTP-SAIFR School on Open Problems in Cosmology

• Paolo Creminelli (ICTP-Trieste)
• Mehrdad Mirbabayi (ICTP-Trieste)
• Rogerio Rosenfeld (IFT-UNESP/ICTP-SAIFR)
• Riccardo Sturani (IFT-UNESP/ICTP-SAIFR)

There is no registration fee and limited funds are available for travel and local expenses.

List of participants here.

Announcement:

Application deadline: May 17, 2025 (closed)

Lecturers

1st week

• Roman Scoccimarro (New York University, USA): Large scale structure theory
• Gonzalo Palma (Universidad de Chile, Santiago, Chile): Physics of Inflation
• Jose M. Ezquiaga (Niels Bohr Institute, Denmark): A premiere on Gravitational Wave Cosmology

2nd week

• Emmanuel Schaan (SLAC National Accelerator Laboratory, USA): Physics of the Cosmic Microwave Background 
• David Alonso (University of Oxford, UK): Large scale structure observables
• Francisco Antonio Villaescusa Navarro (Simons Foundation and Princeton University, USA): Machine Learning Methods for Cosmology

• Agudelo Ruiz, Jhonny Andres (Universidade Federal de Juiz de Fora, Brazil): Constraints from observational data for a running cosmological constant and warm dark matter with curvature

It is known than the inclusion of spatial curvature can modify the evolution of matter perturbations and affect the Large Scale Structure (LSS) formation. We quantify the effects of the nonzero spatial curvature in terms of LSS formation for a cosmological model with a running vacuum energy density and a warm dark matter component. The evolution of density perturbations and the modified shape of their power spectrum are constructed and analyzed.


• Ahumada Acuña, Guadalupe Isabel (Universidad de Buenos Aires, Argentina): GRAVITATIONAL AND ELECTROMAGNETIC THEORIES OF BORN-INFELD Á LA PALATINI

We study gravito-electromagnetic theories inspired by Born-Infeld nonlinear electrodynamics, known for avoiding singularities in point-source solutions. Using the Palatini formalism (i.e. treating the metric and connection as independent variables), we derive the field equations and focus on a static black hole with both electric and magnetic charge to analyze whether the singularity is smoothed or deformed in this framework.


• Almonacid Diaz, Angel David (Universidad Nacional de Colombia, Colombia): Isocurvature Perturbations in Two-Scalar-Field Inflationary Models on a Constant-Curvature Field Space

This poster explores the systematic derivation of curvature observables in multi-field inflationary models, emphasizing the geometric underpinnings that bridge formal mathematical rigor with calculable physical quantities. By leveraging the ADM formalism, we derive energy and momentum constraints that directly link metric perturbations to scalar field dynamics, providing a clear pathway to isolate adiabatic (curvature) and isocurvature modes. Through perturbative expansions in flat gauge, we express lapse and shift variables in terms of field fluctuations, highlighting the analysis of second-order perturbations and their role in mode coupling. Central to this work is the development of explicit analytic expressions for spectral indices, rooted in the covariant perturbation theory of scalar fields. We demonstrate how the geometric structure of harmonic maps—particularly the pullback bundle formalism and Jacobi field equations—combined with the development of perturbations within the ADM framework—encodes the evolution of curvature perturbations, even in non-trivial field-space geometries. For practical applications, we establish a simplified equivalence between these geometric formulations and reduced computational frameworks tailored for two-field scenarios in flat spacetime. This synthesis not only clarifies the origin of adiabatic-isocurvature correlations in multi-field inflation but also provides tools adaptable to particle physics contexts, where effective field theories often demand tractable approximations of curvature-driven observables. Keywords: Multi-field inflation, curvature perturbations, isocurvature modes, ADM formalism, spectral indices, effective field theory.


• Bacchi, Michael (PPGCosmo, Ufes, Vitoria, ES, Italy): Testing inflation on all scales: CMB, PBHs and Gravitational Waves

When searching for viable inflationary models, one should identify good models by their ability to simultaneously explain current observations on all scales. In this presentation, I will show the importance of constraining the parameter space by comparing the large-scale predictions for the power spectrum with current CMB anisotropies measurements and upper limits on μ-distortions, while at the same time taking into account uncertainties due to the reheating phase. Moving to smaller scales, we compute the non-Gaussianity at peak scale and the abundance of PBHs, further restraining the viable region of the parameter space that does not over-produce them. Finally, by calculating the signal-to-noise ratio for different gravitational wave experiments and comparing it with the astrophysical foregrounds, we select the best-suited experiment to test the inflationary model in the future. While this study was performed for the hybrid α-attractors case, this approach, which combines tests at different scales and exploits the synergy between cosmological observations and theoretical consistency requirements, could be applied to any other inflationary model and can be used to establish the small-scale phenomenology of inflationary models on firm grounds.


• Baddis, Saad Eddine (Faculty of Science, Mohammed V University in Rabat, Rabat, Morocco, Morocco): Swampland Statistics for Black Holes

In this work, we approach certain black hole issues, including remnants, by providing a statistical description based on the weak gravity conjecture in the swampland program. Inspired by the Pauli exclusion principle in the context of the Fermi sphere, we derive an inequality which can be exploited to verify the instability manifestation of the black holes via a characteristic function. For several species, we show that this function is in accord with the weak gravity swampland conjecture. Then, we deal with the cutoff issue as an interval estimation problem by putting a lower bound on the black hole mass scale matching with certain results reported in the literature. Using the developed formalism for the proposed instability scenarios, we provide a suppression mechanism to the remnant production rate. Furthermore, we reconsider the stability study of the Reissner–Nordström black holes. Among others, we show that the proposed instabilities prohibit naked singularity behaviors.


• Barbosa, Janiely (Universidade de São Paulo, Brazil): Kinematic effects on the polarization of the Cosmic Microwave Background

The motion of the solar system relative to the Cosmic Microwave Background (CMB) rest frame induces a break of the statistical isotropy in the temperature and polarization power spectra due to effects of kinematic origin. These effects are due mostly to the presence of a Doppler dipole, but also includes Doppler modulation and relativistic aberration. A deep understanding of the impact of kinematic effects on the CMB is essential for extracting accurate information from maps of this primordial radiation field, both on small scales, where the dominant kinematic effect is relativistic aberration, and on large scales, where previous analyses have revealed anomalies with functional forms resembling kinematic effects, such as the so-called dipolar modulation. In this work, we explore the statistical correlations between neighboring multipoles in spherical harmonic space introduced by these kinematic effects, using them as estimators for the solar system’s peculiar velocity. For this purpose, we apply maximum-likelihood estimators to full-sky simulations and real observational data from the Planck satellite. We aim to quantify the impact of kinematic effects on all three Stokes parameters (I, Q and U), i.e., work not only with the CMB intensity (I), but also with the CMB polarization (Q and U), proposing a maximum-likelihood estimator that incorporates all three parameters simultaneously. Our theoretical calculations are based on an expansion in the solar system peculiar velocity. We verified that a truncation at first order terms is good for describing multipole correlations of the CMB intensity I at a broad range of multipoles (l < 2048). However, as far as polarization is concerned, a linear approximation does not show a similar level of accuracy at small scales (l >~ 1000). Therefore, we are extending the calculations to include quadratic corrections. The analysis of real observational data introduces partial-sky coverage issues due to the mask, which deeply distorts cross-correlation analysis. This motivates a separate study on the treatment of the mixing matrix.


• Berrabah, Abdelghani (University of Science and Technology Houari Boumediene, Algeria): i’ll send you my poster title and abstract soon

i’ll send you my poster title and abstract soon


• Carlos Ribeiro, Sanderson (Universidade Estadual de Londrina (UEL), Brazil): Reconstruction Of The Dark Energy Equation Of State

In 1998, observations of type Ia supernovae revealed that the universe is expanding at an accelerated rate. This phenomenon was attributed to dark energy, an exotic component with negative pressure, included in the context of the Standard Cosmological Model, based on Einstein’s General Relativity and the Cosmological Principle. In this work, we reconstruct the equation of state of dark energy w(z), assuming it as a barotropic fluid with an equation of state given by w(z)=p_{DE}/\rho_{DE}. We use a parametric and model-independent approach. The method employed, cubic splines, is commonly used in the numerical interpolation of functions. The analysis was carried out in stages, incorporating data and applying the Markov Chain Monte Carlo method to obtain more reliable uncertainties in the estimates. We observed that, for low redshifts (0 ≤ z ≤ 3), w(z) exhibits a bimodal behavior, concentrating at w=−1 and 0 < w < 1/3, a novel result that does not contradict current cosmology, as our model also produced results consistent with other literature, such as \hat{w} = −1.087±0.03592 for constant w.


• Cartes Silva, Alejandro Moisés Lenin (University of Chile, Chile): Supernovae Complete Pipeline: from light curves to cosmology

In this work, we present an end-to-end deep learning pipeline designed to perform a binary classification of supernovae using recurrent neural networks (RNNs) and estimate cosmological parameters from CDM models using supernovae classified as Type Ia. The model’s performance is evaluated using a variety of metrics, demonstrating its potential for improving supernova cosmology studies and refining measurements of key cosmological parameters. This research contributes to the growing intersection of machine learning and observational cosmology, aiming to enhance the accuracy and efficiency of supernova-based cosmological probes.


• Castillo Felisola, Oscar (Universidad Tecnica Federico Santa Maria, Chile): Metric or non-metric, that is the question

In General Relativity the metric plays a double role, provides a notion of distance and mediates the gravitational interaction. In an attempt to separate these roles, we have proposes a polynomial affine model of gravity, in which the metric plays no role in the mediation of the interaction. We inquire the cosmological ansatz of the connection and explore the space of solutions. Interestingly, the models might accommodate the tendencies observed by DES and DESI.


• Chantada, Augusto Tomás (Universidad de Buenos Aires, Argentina): Cosmology-informed neural networks to solve the background dynamics of the Universe

In the last few years, there has been significant progress in the development of machine learning methods tailored to astrophysics and cosmology. We have tailored one of these methods, namely, the neural network bundle method, to the cosmological scenario. Moreover, we shown that in some cases the computational times of the Bayesian inference process can be reduced significantly. In this work, we show the results of applying this method to obtain the background cosmological evolution of 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. We show that the statistical analyses carried out with this method require lower computational times than the ones performed with the solutions provided with the traditional numerical method. This reduction in time is more significant in the case of a difficult computational problem such as the ones addressed in this work.


• Colipí Marchant, Francisco Ignacio (Universidad San Sebastián, Chile): Cosmological cutting rules for n-point correlation functions in the Schwinger-Keldysh formalism

To study non-Gaussianities from cosmic inflation, we compute *n*-point correlation functions using the Schwinger-Keldysh formalism, extending QFT techniques to curved spacetime. Challenges arise from nested time integrals and unknown inflationary Lagrangians. Crucially, unitarity imposes constraints, enforced via cutting rules similar to the Cosmological Bootstrap Program. These rules—backed by the Cosmological Optical Theorem—simplify calculations by relating higher/lower-order amplitudes. Here, we develop unitarity-based cutting rules using a discontinuity operator (Disc[f]), testing them on 3-point vertices with derivatives. Our approach streamlines diagrammatic computations while preserving consistency with fundamental QFT principles.


• Costanza, Belén (Facultad de Ciencias Astronómicas y Geofísicas. Universidad Nacional de La Plata, Argentina): Development of neural networks for CMB polarization maps and power spectrum computation

I will present the neural network developed to simulate the Wiener Filter (WF) for polarization Cosmic Microwave Background (CMB) maps, used to reduce the inhomogeneous noise present in those maps and reconstruct the B-mode signal, with an additional procedure for the E-to-B leakage problem. We present the performance of this neural network, written in Tensorflow 2, comparing the results with the traditional method that uses conjugate gradient (CG). Furthermore, we estimate the power spectrum of an unknown signal and study the accuracy on different scales of interest.


• Crisman, Camilo (Universidade Federal do Espírito Santo – UFES, Brazil): Peculiar velocity from SNe, an approach to structure formation parameters.

Supernovae have a widely used tool on cosmology due to the information they provide through the Hubble Diagram. However, additional information encoded in their peculiar velocities is often overlooked in standard analyses. In this work, we incorporate this component in the correlation to improve cosmological parameter estimation. Using data from Pantheon+ and DES-Y5, we derive constraints on the standard ΛCDM parameters while also investigating their impact on structure formation quantities, particularly σ₈ and γ. Our approach demonstrates that peculiar velocities can refine cosmological constraints and provide new insights into the growth of large-scale structure. This method presents a complementary avenue to traditional techniques, offering potential improvements in precision when combined with future galaxy survey data.


• De Lima, Cinthia N. (Universidade Estadual de Londrina, Brazil): Investigating the Functional Form of the Richness-Mass Distribution

Galaxy clusters are one of the most important cosmological probes, as they are the largest gravitationally bound structures in the universe and, therefore, have characteristics intrinsically linked to the formation of large-scale structures. The mass of galaxy clusters cannot be measured directly, and because of this, a mass proxy is often used. An important property, widely used as a mass proxy, is richness—a quantity that estimates the number of galaxies that are members of the cluster. It can be associated with the mass of a cluster through the richness-mass relation, due to the assumption that the more massive the region, the higher the probability of galaxies being present in it due to gravitational collapse. In this work, we investigate the functional form of the richness-mass relation and its associated distribution, considering both linear and quadratic models that account for the dependencies on mass and redshift, as well as the impact of incorporating the richness threshold on the shape of the distribution, compared to approaches that ignore this factor.


• De Sousa Neto, Agripino Segundo (Observatório Nacional (ON), Brazil): No evidence for dynamical dark energy from DESI and SN data: a symbolic regression analysis

Recent measurements of Baryon Acoustic Oscillations (BAO) from the Dark Energy Spectroscopic Survey (DESI), combined with data from the cosmic microwave background (CMB) and Type Ia supernovae (SNe), challenge the $\Lambda$-Cold Dark Matter ($\Lambda$CDM) paradigm. They indicate a potential evolution in the dark energy equation of state (EoS), $w(z)$, as suggested by analyses that employ parametric models. In this paper, we use a model-independent approach known as high performance symbolic regression (PySR) to reconstruct $w(z)$ directly from observational data, allowing us to bypass prior assumptions about the underlying cosmological model. Our findings confirm that the DESI data alone agree with the $\Lambda$CDM model ($w(z) = -1$) at the redshift range considered. Notably, this agreement improves slightly when we exclude the data point at $z = 0.51$. Additionally, we observe similar conclusions when combining the DESI data with existing compilations of SNe distance measurements, such as Pantheon+ and the Dark Energy Survey Supernova 5-Year, regardless of the absolute magnitude prior values used. Therefore, these results suggest that it is premature to claim any statistically significant evidence for a dynamical EoS or deviations from the $\Lambda$CDM model based on the current DESI data, either alone or in combination with supernova measurements.


• De Souza, Josiel Mendonça Soares (Universidade Federal do Rio de Janeiro, Brazil): Beyond Fisher Approach for Gravitational Waves and Cosmology

In the next decade, third-generation gravitational wave (GW) observatories, such as the Einstein Telescope and Cosmic Explorer, will begin operation, enabling the detection of compact object coalescences at unprecedented distances (up to z < 100). Analyzing these sources cosmologically necessitates GW parameter inference, which typically involves around 15 parameters for each detection—a process that is computationally intensive. To address this challenge, we discuss the application of Derivative Approximation for Likelihoods (DALI) in gravitational wave and cosmological data analysis. DALI is a more time-efficient approach that incorporates higher-order terms in the Taylor expansion of likelihoods, which is particularly advantageous when the expected posterior distributions deviate from Gaussianity, rendering the Fisher Matrix approximation unreliable. Such deviations often occur in the context of GW signals from compact binary coalescences, especially in cases of parameter degeneracies, such as the distance-inclination degeneracy. In this work, we explore the behavior of gravitational wave DALI-posteriors under various parameterizations of GW signals and demonstrate how their accuracy can be enhanced using automatic differentiation (autodiff).


• De Souza, Rayff Aby Faraj (Observatório Nacional, Brazil): Dark matter freeze-in during warm inflation and the seesaw mechanism

A compelling way to address the inflationary period is via the warm inflation scenario, where the interaction of the inflaton field with other degrees of freedom affects its dynamics in such a way that slow-roll inflation is maintained by dissipative effects in a thermal bath. In this context, if a dark matter particle is coupled to the bath due to non-renormalizable interactions, the observed dark matter abundance may be produced during warm inflation via ultra-violet freeze-in. In this work, we propose applying this scenario in the framework of a U(1)B−L gauge extension of the Standard Model of Particle Physics, where we also employ the seesaw mechanism for generating neutrino masses.


• Demétrio, Luiz Felipe (Universidade Estadual de Londrina, Brazil): Primordial Black Hole Formation in a Dust Bouncing Model

Linear scalar cosmological perturbations have increasing spectra in the contracting phase of bouncing models. We study the conditions for which these perturbations may collapse into primordial black holes and the hypothesis that these objects constitute a fraction of dark matter. We compute the critical density contrast that describes the collapse of matter perturbations in the flat-dust bounce model with a parametric solution, obtained from the Lemaitre-Tolman-Bondi metric that represents the spherical collapse. We discuss the inability of the Newtonian gauge to describe perturbations in contracting models as the perturbative hypothesis does not hold in such cases. We carry the calculations for a different Gauge choice and compute the perturbations power spectra numerically. Finally, assuming a Gaussian distribution, we compute the primordial black hole abundance with the Press-Schechter formalism and compare it with observational constraints. From our analysis, we conclude that the primordial black hole formation in a dust-dominated contracting phase does not lead to a significant mass fraction of primordial black holes in dark matter today.


• Dias, Mariana Lopes Da Silva (Observatório Nacional, Brazil): 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 $\Lambda$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.


• Dias, Iago Lopes Soares (Observatório do Valongo – UFRJ, Brazil): Investigating photometric redshift distributions for LSST 3x2pt analysis with Roman-Rubin simulations.

Cosmological measurements with Rubin LSST data rely on photometric redshift (photo-z) measurements that should attain unprecedented precision and accuracy. Consequently, massive development efforts are underway within and outside the Rubin Science Collaborations. In the Dark Energy Science Collaboration (DESC), a wide array of projects seek to investigate and optimize photo-z analysis choices for different applications, including galaxy cluster redshift estimation, galaxy clustering and weak gravitational lensing correlations (i.e., 3x2pt analyses), and many more. In particular, evaluating the performance of photo-z algorithms in OpenUniverse Roman-Rubin simulations is a key step in preparing for LSST data arrival. In this work, we investigate the performance of one of the leading machine learning (ML) photo-z algorithms, FlexZBoost. We evaluate the algorithm’s performance in a range of lens and source samples scenarios, including different magnitude cuts, and variations in training set representativeness and sky distribution. The ensemble redshift distributions measured in this analysis were used in cosmological inference pipelines to assess potential biases in cosmological parameters caused by imperfect ensemble redshift characterization.


• Ding, Keyi (University of Groningen, Netherlands): CMB-S4 Fisher Forecast for Primordial non-Gaussianity

Primordial non-Gaussianity is one of the most promising probes for studying inflation and the physics occurring in the early Universe. Measurements of the Cosmic Microwave Background (CMB) have provided the strongest constraints on the amplitude of primordial non-Gaussianity, f_NL. The upcoming CMB-S4 experiment aims to constrain f_NL more accurately than ever before. In this study, a Fisher forecast was performed in order to estimate the constraining power of CMB-S4 in the case of three primordial bispectrum shapes: local, equilateral, and orthogonal.


• Fernandes Filho, Ricardo Alexandre (Federal University of Espírito Santo, Brazil): Modified Theories of Gravity: The Horndeski Models

In this thesis, a qualitative analysis is proposed on how theories related to gravity have changed over time until reaching the well-known modified theories of gravitation, demonstrating the power they hold. The aim is to serve as an entry point to the subject and provide a basis for more complex works in the future. Starting with the understanding of gravity and progressing to Albert Einstein’s groundbreaking theory of General Relativity, which explained some aspects not addressed by Newtonian theory but still left unexplained observations on large scales. After Einstein, efforts have been mostly focused on constructing extensions of General Relativity, paving the way for the well-known modified theories of gravitation. These theories manifest in various forms in the literature, but here the focus will be on those constructed by the inclusion of a scalar field into the theory, giving rise to the so called scalar-tensor theories. Among the modified scalar-tensor theories, the discussion will be restricted to those that preserve second-order equations of motion, with the most general known as the Horndeski theory, which will be the main theory addressed here. After dissecting the Horndeski theory, we analyze its equations of motion and apply the latter to certain cases of interest. The general aspect of the Horndeski theory will also be exploited to derive, from it, already known theories, such as Brans-Dicke, Cubic Galileon, and $f(R)$ models. The final part of the work will be dedicated to delving into quantum cosmology using the Horndeski theory.


• Fonseca Moreno, Diego Fernando (Universidad Nacional de Colombia, Colombia): A Brief Review of First and Second-Order Cosmological Perturbations Including Baryonic Matter from an Eulerian Perspective Through Jeans Filtering Functions

In modern cosmology, the problem of large-scale structure formation has been studied through various analytical and computational methods, making it a cornerstone of astrophysics. The complexity of the equations that describe the evolution of small fluctuations in the matter field, with respect to the Friedmann-Lemaître-Robertson-Walker (FLRW) universe, commonly known as the theory of linearized gravitational perturbations, makes it a valuable framework for addressing the problem. Specifically, the sub-horizon scale approximation allows us to explore scenarios where semi-analytical tools play a significant role in better understanding how structures in our universe have evolved and how the cosmic web structure has formed. In this context, these techniques have facilitated comparisons with extensive simulations and provided a basis for contrasting with high-precision observations. Therefore, we present a semi-analytical description of the evolution of density contrast in cold dark matter (CDM), including baryonic matter, in both linear and nonlinear regimes in Fourier space, up to first and second order. We achieve this by using the Jeans filtering function (JFF), considering only growing solutions, and then comparing them with the numerical solutions calculated for the JFF equations up to zero and first-order iterations, with the aim of explaining why baryonic matter must be included to enhance precision in higher-order perturbations.


• Franco, Camila Nascimento (Observatório Nacional, Brazil): Measuring the matter fluctuations in the Local Universe with the ALFALFA catalog

The standard model of cosmology describes the matter fluctuations through the matter power spectrum, where $\sigma_{8} \equiv \sigma_{8,0} \equiv \sigma_{8}(z = 0)$, defined at the scale of $8\,h^{-1}$ Mpc, acts as a normalisation parameter. Currently, the literature reports measurements of $\sigma_{8}$ analysing different cosmic tracers, where some of these results were obtained assuming a fiducial cosmology. In this study we measure, in a model-independent approach, the matter fluctuations in the Local Universe using HI extragalactic sources mapped by the ALFALFA survey; our analyses allow us to test the standard cosmological model under extreme conditions in the highly non-linear Local Universe, quantifying the amplitude of the matter fluctuations there. Our work directly measures $\sigma_{8}$ including the 3-dimensional distances of the HI sources determined by the ALFALFA survey without assuming a fiducial cosmology, resulting in a robust model-independent measurement of $\sigma_{8}$. Our methodology involves the construction of suitable mock catalogues to simulate the large scale structure features observed in the data, applying the 2-point correlation function, and making use of Markov Chain Monte Carlo methods to estimate the parameters. Analysing these data we measure $\sigma_8 = 0.78 \pm 0.04$ for $h = 0.6727$, $\sigma_8 = 0.80 \pm 0.05$ for $h = 0.698$, and $\sigma_8 = 0.83 \pm 0.05$ for $h = 0.7304$. Considering the data pairs $(\sigma_8, H_0)$ from the Planck CMB and ACT CMB-lensing analyses, our measurement agrees with them in less than $1\,\sigma$ confidence level. From a model-independent perspective, we find that the scale where the matter fluctuation is $1$ is $R = 7.2 \pm 1.5~\text{Mpc}$.


• Gómez Aguilar, Tadeo Dariney (National Autonomous University of Mexico, Mexico): SGWB from Hierarchical and Hyperbolic Dynamics of PBHs in Dwarf Galaxies

We explore the evolution of primordial black holes (PBHs) in dense astrophysical environments, with a particular focus on their gravitational wave (GW) signatures from binary mergers and close hyperbolic encounters (CHEs). Our study extends previous work by evaluating the hierarchical merger history of PBHs in dark matter-dominated dwarf galaxies and computing, for the first time, the stochastic GW background produced by CHEs events. The proposed framework allows us to determine under what conditions GW bursts from CHEs and sequential PBH mergers contribute significantly to the observable stochastic background and produce remnant of binaries of PBHs. We identify detectable parameter regimes for next-generation GW detectors like the Einstein Telescope, Cosmic Explorer, and LISA, and offer numerical criteria delineating the validity range of our analytical models.


• Guterres, Djalma Humberto Silva (INPE, Brazil): Gravitational waves from binary systems of compact objects in Brans-Dicke theory

Gravitational waves, initially predicted by Albert Einstein, are disturbances in spacetime generated by the accelerated motion of masses. However, for their emission to be detectable, a large amount of mass and energy is required, with the primary detectable sources being astrophysical systems composed of compact objects, such as neutron stars and black holes. In 2016, the LIGO-Virgo collaboration announced the first direct detection of gravitational waves, known as event GW150914, which was the coalescence of a binary black hole system. The first detection of gravitational waves generated by a binary neutron star system was event GW170817, marking the first multi-messenger event involving gravitational waves. We can describe gravitational waves as small perturbations in a flat background, represented by the Minkowski metric. This formalism is known as the linearized theory of gravity. Through the helicity decomposition of the metric perturbation, we can obtain three types of gauge-invariant quantities: scalar, vector, and tensor components, highlighting the six physical degrees of freedom of the perturbation, two in each sector. In General Relativity, only the tensor component has wave-like solutions, exhibiting two polarization states. In Brans-Dicke theory, the scalar components also present wave-like solutions, generating two additional polarization states alongside the tensor ones, resulting in a total of four polarization states. For a binary system, the scalar polarizations, given a multipolar expansion, present a dipole term and a quadrupole term, proportional to the parameters $\mathcal{S}$ and $\Gamma$, respectively, which depend on the mass and type of objects composing the binary system. In the case of a binary black hole system, there is no emission of scalar radiation, as the parameters $\mathcal{S}$ and $\Gamma$ cancel out. Therefore, to study scalar polarizations in Brans-Dicke theory, at least one component of the binary system must be a neutron star. Consequently, event GW170817 represents a case of interest for estimating scalar gravitational waves, as it is a system conclusively composed of two neutron stars. By analyzing and comparing the signals generated by a gravitational wave emitted by a binary neutron star system, we can assess the possibility of detecting the two scalar polarization modes with the sensitivity curves of gravitational wave detectors. The detection or absence of scalar polarization modes in the signal of a gravitational wave can be used as a method to test the theory of General Relativity.


• H. Santos, Gustavo (UFABC, Brazil): Heavy vector dark matter from low scale inflation

In single field inflation, a pseudoscalar inflaton can couple to U (1) gauge bosons through the Chern-Simons coupling. This can lead to tachyonic production of gauge bosons with masses mA of the order of the Hubble rate during inflation H_I . In the absence of coupling to the visible sector, such vector bosons can produce the entirety of dark matter. We show that the parameter space of heavy dark matter m_A ≳ H_I requires low scale inflation H_I ≲ 10^8 GeV. We also analyze the resulting constraints to scalar non-gaussianity and primordial gravitational waves.


• Hilgert Pacheco, Mayara (INPE, Brazil): Estimating Cosmological Parameters from Bright Sirens with the Einstein Telescope and Cosmic Explorer

Gravitational waves (GWs), predicted by Einstein in 1916 and first detected by LIGO in 2015, have opened new avenues for multi-messenger astronomy. Concurrently, the Hubble constant (H0), which quantifies the Universe’s expansion rate, presents a well-known discrepancy between different observational methods, a challenge referred to as the Hubble Tension. A promising approach to addressing this issue is the use of gravitational waves as standard sirens, which provide an independent means of measuring cosmological distances. This work explores the use of the bright standard siren, specifically bright sirens, to estimate key cosmological parameters, including H0, Om, w0, and wa. We employ the Derivative Approximation for Likelihood (DALI) method to estimate both gravitational wave and cosmological parameters. Furthermore, we assess the potential of next-generation detectors—such as the Einstein Telescope and Cosmic Explorer—to improve cosmological constraints through the luminosity distance–redshift relation.


• Jiménez Cardona, Ferney Andrés (Universidad del Valle, Colombia): Chameleon Mechanisms in Modified Gravity f(R) Models

Explaining the accelerated expansion of the universe remains one of the greatest challenges in modern cosmology. Although the cosmological constant is the simplest model to account for observational data, it faces the well-known fine-tuning problem. Modified gravity of the form f(R) offers an alternative approach to addressing the dark energy problem. This framework exhibits characteristic effects on both cosmological and local scales, which can distinguish it clearly from other dark energy models, including the cosmological constant. One such effect, known as the chameleon effect, is the focus of this project. We aim to examine the formalism and implications of this effect in specific f(R) models.


• Kumar, Nitesh (University of Tarapacá, Chile): Dissecting the ΛCDM Model via Targeted Parameter Variations: Insights from CMB Power Spectrum Analysis

The Cosmic Microwave Background (CMB) remains a pivotal observational window into the early universe. While the ΛCDM model has proven successful in describing the CMB power spectrum, our work revisits this framework with a focused computational approach to isolate and understand the physical influence of each cosmological parameter. Instead of relying on full-package parameter estimation from the outset, we employed a modular strategy: first probing spatial curvature effects using CAMB and then extending the analysis to the six standard ΛCDM parameters via CLASS. Our investigation reveals not only the expected impacts, such as curvature shifting the spectrum and Ω_b/Ω_c modulating peak heights, but also uncovers subtle interdependencies that manifest when parameters are varied independently. This provides an educationally transparent but quantitatively rigorous mapping between theory and CMB observables. To validate our results, we reproduced and cross-verified the CLASS output against Planck data, reinforcing the precision of the code and model. Unlike black-box statistical fitting, this controlled variation approach highlights the mechanistic role of each parameter and sets the stage for a structured MCMC implementation. Our upcoming work will leverage this groundwork to construct a more informed and efficient MCMC pipeline using tools like SCoPE, MontePython, or CosmoMC, focusing not just on fit, but on interpretability. This poster presents not only results but also a methodology for building intuition-driven cosmological pipelines.


• ladghami, yahya (Mohammed I University, Oujda, Morocco, Morocco): Black Holes Thermodynamics with spacetime foam.

We investigate the emergent thermodynamic phenomena arising from spacetime foam and its impact on black hole behavior. Within this framework, we adopt the Barrow model, where the structure of spacetime at small scales is modeled by analogy with the Koch snowflake, implying that black hole surfaces acquire a quasi-fractal structure due to quantum deformations induced by quantum gravity effects. Our analysis, conducted within the extended phase space formalism, reveals that the quasi-fractal correction to black hole entropy significantly modifies the equation of state, critical parameters, and phase transition behavior of charged AdS black holes.


• Laurindo, Letícia (USP, Brazil): Colours of GCs: how to match models and observations?

Globular clusters (GCs) have long played a crucial role in studies of stellar populations and remain key to understanding galaxy formation, stellar evolution, and stellar dynamics. While they were once considered prototypes of simple stellar populations, current evidence reveals the presence of multiple populations in most massive GCs. This complexity challenges standard stellar population synthesis models, particularly in reproducing integrated photometric properties across broad wavelength ranges. Previous works using data from the Next Generation Virgo Cluster Survey (NGVS) and the Milky Way (MW) have highlighted discrepancies in colours, ages, and metallicities derived from photometry, suggesting that standard models, often calibrated for MW GCs, may not be suitable for extragalactic clusters. One proposed explanation involves differences in chemical abundance patterns, such as variations in C and N. In this project, we explore how different chemical assumptions affect photometric age determinations and investigate signatures of multiple populations using J-spectra. By comparing model predictions with J-PAS and J-PLUS data of extragalactic cluster candidates — particularly in nearby disc galaxies — we aim to assess the role of chemistry in shaping integrated photometric properties, using both colour-colour diagrams and spectral energy distribution (SED) fitting techniques such as MUFFIT.


• Lima, Rose Clívia Santos Sales (Universidade Federal de São Paulo, Brazil): Hubble Tension and the Quasar APM 08279+5255




• Lopes, Maria Eduarda Gomes (Observatório Nacional, Brazil): Dipolar fluence distribution of statistically isotropic FERMI gamma-ray bursts

We study the large-angle distribution of gamma-ray bursts (GRBs) from the last FERMI/GBM catalogue to investigate the statistical isotropy of these transient astrophysical events, as well as the angular distribution of the GRB fluence; we are particularly interested in exploring whether this radiative property exhibits any preferred direction on the sky that might suggest its origin. Our results show that GRBs are distributed isotropically across the celestial sphere. However, the distribution of GRB fluence — defined as the median GRB fluence in a set of directions scanning the celestial sphere — reveals a curious dipolar structure, with a directional preference near the Galactic plane. This preference, however, is not correlated with the Milky Way itself, suggesting an extragalactic origin. Furthermore, analyses of BATSE Channel 4 fluence data (E > 300 keV) reveal a dipole direction aligned with that of the cosmic microwave background (CMB) dipole.


• Merlo Azzolina, Lucas (Facultad de Ciencias astronómicas y geofísicas, Argentina): Flux jumps in the data chain of QUBIC telescope

The flux jumps generated by the periodicity of the SQUID transfer function in a Flux-Locked-Loop system directly affect the output signal detected in the QUBIC telescope data chain. To ensure precise data analysis, we have developed specialized algorithms to accurately identify the exact timing of the start and end of each jump, along with their corresponding amplitudes, enabling detailed characterization. Once identified, we apply a correction to the signal by adding the offset and replacing the affected data with the RMS of adjacent data, ensuring continuity and preserving the quality of the corrected dataset for subsequent analysis.


• Miranda, Gabriel Resende (UFBA – Universidade Federal da Bahia, Brazil): Bimodality in J-PAS: Optimizing catalogs for star-galaxy classification via Machine Learning

This work aimed to improve the quality of catalogs used in machine learning models for star-galaxy classification within the context of astronomical data provided by J-PAS (Javalambre Physics of the Accelerating Universe Astrophysical Survey). As part of the Data Validation (DAVA) team, our main contribution was cleaning the training and testing catalogs used by team members to develop their classification models, focusing on removing objects identified as bimodal. These objects are formed by nearby sources that SExtractor (a widely used tool for detecting objects in astronomical images) erroneously identifies as a single object. When this happens, particularly in cases where stars are mistakenly identified as galaxies, the performance of classification models can be negatively affected. Our methodology consisted of analyzing individual cutouts for each object in each catalog, applying a pipeline that detects bimodality based on counts profiles along pixel ranges on the x, y axes and diagonals of each image. Multiple peaks detected in any of the profiles indicated the possibility of more than one object present in the cutout. Subsequently, we checked whether the J-PAS database itself already recognized multiple objects in the region of interest; only sources not previously separated were flagged as bimodal. The results showed significant effectiveness in identifying bimodal stars with mag_i < 21, but limitations for galaxies and fainter objects. After this analysis, we decided to remove 904 stars from the training catalog (648 wrongly classified as galaxies) and 244 from the testing catalog (185 false galaxies), which resulted in an increase of ~1% in completeness for both cases, without a negative impact on catalog purity. We concluded that removing bimodal stars improves the data quality for training more robust models, although further enhancements are needed, especially in handling galactic objects with more irregular morphologies.


• Miranda Carrion, Gabriel Karim (Instituto de Ciencias Físicas, UNAM, Mexico): Accelerating inference on Interacting Dark Energy with neural emulators

Stage IV galaxy surveys, such as Euclid and the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), will generate datasets of unprecedented size and precision. These surveys hold the potential to place strong constraints on models of the governing physics on cosmological scales. However, analyzing these vast datasets requires the exploration of high-dimensional and complex parameter spaces to accurately model systematic effects, particularly on non-linear scales, which often demand computationally intensive theoretical prediction. In this work, we use a novel framework for cosmological likelihood inference designed to accelerate Bayesian inference from cosmological surveys to derive constraints on beyond-standard models of gravity. We employ recent advances in machine learning, starting with CosmoPower to efficiently emulate the non-linear matter power spectrum based on the halo model reaction. We focus on constraining an Interacting Dark Energy model, called Dark Scattering. Our first analysis combines KiDS-1000 data with information from CMB+BAO, constraining the dark energy — dark matter interaction parameter, A_{ds} =10.6^{+4.5}_{−7.3} b/GeV at 68% confidence, while also alleviating the S8 tension. A second analysis will also be presented, showing forecasts for Stage IV cosmic shear surveys, obtained through an automatically differentiable inference pipeline to further accelerate the Bayesian analysis.


• Moraes, Tatiane De Paula (Universidade Federal do Espírito Santo – UFES, Brazil): Gravitational Waves as Indicators of Distance, Density and Cosmological Velocities

Gravitational waves represent an important tool in astrophysics and their relevance to cosmology has also been highlighted in several recent studies. With the advent of third-generation observatories, such as the Einstein Telescope, we will see a substantial increase in detections per year, especially of black hole mergers. These events will allow us to look even farther into the universe, and their use as dark sirens will enable us to explore not only the local universe but also its large-scale structure. With this in mind, this project aims to study and develop computational techniques for analyzing dark siren data, in order to use them statistically as tracers of density and velocity fields in cosmology. Our objective is to evaluate their constraining power as tracers of large-scale structures and compare it to their standard use as simple distance indicators.


• Moreno Chalacá, Sebastián (Universidad del Valle, Colombia): Mass-Radius relation for neutron stars in axion modified gravity




• Noriega Barros, Hernán Enrique (Instituto de Física – UNAM, México & Instituto de Ciencias Físicas – UNAM, México, Mexico): Are current neutrino mass constraints reliable? insights from full shape

Cosmological findings from the combination of DESI and Planck data have placed very tight constraints on the total neutrino mass within the ΛCDM model, leading to tension with particle physics experiments. Based on full-shape analyses of (e)BOSS data, we show that the neutrino mass signal is highly sensitive to background effects, clouding the reliability of its measurement. However, by disregarding the background and focusing on the effect of structe suppression, we discover that most of the neutrino information is derived from the amplitude of the wiggles, rather than the broadband suppression of the power spectrum, as has been believed for many years. This insight offers a promising pathway for robustly extracting the neutrino signal. This work is mainly based on arxiv: 2407.06117, and 2503.14744, 2504.18464


• Ortiz Camacho, Juan Guillermo (Universidad de Antofagasta, Chile): Exploring the Cosmological Consequences of Non-Conventional Supersymmetry

In this work, we explore an interacting system between gravity and spinors using the unconventional supersymmetry connection (uSUSY). This modified version of supersymmetry adjusts the fermionic field, traditionally represented by the gravitino, and reformulated it using a matter ansatz proposed by Alvarez, Valenzuela and Zanelli [1,2,3]. This approach allows the inclusion of spin s=1/2 spinors, as found in the Standard Model, rather than depending on hypothetical particles. Our objective is to investigate cosmological solutions for a homogeneous and isotropic universe in both 3D and 4D. In particular, in this work we will only study 3D solutions, because we first want a clearer understanding, more experience with the theory and familiarity with this novel uSUSY proposal before looking for 4D cosmological solutions. A key aspect of this work is to examine how the scale factor of the universe evolves when the geometry of spacetime is affected by this new spinor. It is important to note that the search for exact solutions is extremely complex, so we restrict the analy- sis to simplified systems. Despite these limitations, we believe that this approach offers valuable information about the interaction between gravity and spinors, and how these interactions influence the cosmological evolution of the universe. Referencias [1] P. D. Alvarez, M. Valenzuela and J. Zanelli, JHEP 04, 058 (2012). [2] P. D. Alvarez, L. Delage, M. Valenzuela and J. Zanelli, Symmetry 13, no.4, 628 (2021) [3] P. D. Alvarez and J. Ortiz, Class. Quant. Grav. 39, no.24, 245007 (2022).


• Padilla Albores, Luis Enrique (Queen Mary University of London, United Kingdom): Primordial black hole formation in a scalar field dominated universe.

We present a numerical code designed to solve the Misner–Sharp system for spherically symmetric cosmological models containing both a minimally coupled scalar field and a perfect fluid. Although the code is designed to evolve general scenarios, we focus on the post-inflationary epoch where a rapidly oscillating scalar field dominates the dynamics over a few e-folds. Our study investigates primordial black hole (PBH) formation thresholds under quadratic and quartic scalar potentials, with initial perturbations evolved from superhorizon scales. For the quartic case, we find a formation threshold similar to that in a radiation-dominated universe, consistent with established results. In contrast, the quadratic potential exhibits significant deviations from dust-like behavior due to wave-like effects that counteract gravitational collapse. While computational constraints limit our exploration of the full parameter space, our results suggest that PBH formation may be suppressed in the quadratic case, with the possibility of forming long-lived solitonic structures instead. These findings underscore the need to account for scalar field wave dynamics when modeling PBH formation in early-universe scenarios.


• Pederneiras, Isabel Bonomo (Instituto de Astronomia, Geofísica e Ciências Atmosféricas, USP, Brazil): Unified weak lensing constraints on the M-Lx relation for galaxy clusters

Scaling relations between galaxy cluster properties are crucial for understanding cosmology and baryonic physics. Rigorous calibration of the M-Lx relation, employing weak lensing mass and consistent statistical methodology, is challenging due to heterogeneous cluster samples. The release of the LEGACY imaging data introduced a possibility to unify the cluster selection. We present the all-sky extension of the CODEX catalog based on LEGACY data and introduce a Bayesian framework for calibrating the X-ray luminosity–mass relation, derived for 100 clusters with weak lensing mass measurements. Using the X-ray luminosity estimates for those clusters from ROSAT All-Sky Survey (RASS) data, we perform a power-law fit to the M-Lx relation. Additionally, taking advantage of the recently released eROSITA data (eRASS1), we assess the impact of point source contamination in cluster fluxes for 42 clusters in the eRASS1 footprint. The RASS fit yields a slope 1.7σ lower than the best self-similar prediction, with marginal evidence for redshift evolution of the normalization. As for the eRASS1 analysis, the slope is substantially steeper and in further agreement with the prediction of self-similarity. No additional evolution is also seen. While our results provide the practical means for cosmological studies of both RASS and eRASS data, the link to cluster physics is much cleaner after the cluster flux contamination is reduced.


• Pereira De Carvalho, Laura (UFBA, Brazil): A comparison of the structure formation process in Einstein-de Sitter and ΛCDM cosmologies.

This work addresses the process of cosmological structure formation through both ana- lytical approaches and numerical methods, comparing the outcomes in the Einstein-de Sitter and ΛCDM cosmologies. Initially, this process is examined through linear theory and subsequently through the spherical collapse model. The study concludes with the application of the Press-Schechter formalism, aiming for a statistical description of the abundance of dark matter halos.


• Peronaci, Matteo (“Tor Vergata” University of Rome, Italy): Testing LambdaCDM cosmological model with Genetic Algorithms

The quest to understand the cosmos has led to the remarkable discovery that the universe is expanding at an accelerating rate. This revelation necessitated the integration of dark energy into the standard cosmological model, known as ΛCDM. While ΛCDM model has achieved remarkable success in explaining various observations, it still faces challenges and uncertainties related to dark energy and dark matter. To assess its validity, researchers have employed various methodologies, including consistency checks, tests of general relativity, and model-independent approaches. In this work, we propose the use of Genetic Algorithms, a machine learning technique, to test the ΛCDM model by comparing its predictions with observational data. Specifically, we utilize genetic algorithms to analyse cosmic observables, such as the Hubble rate parameter H(z) and the growth rate of cosmological structures f(z), in order to obtain two independent reconstructions of the dark energy equation of state w(z) for testing the standard model independently of theoretical assumptions. We conduct a comparative analysis by applying genetic algorithms to real data, and examine the results obtained comparing those with the ones resulted from other machine learning techniques. We find that current data is not precise enough for robust reconstruction of the two forms of w. Then we perform extensive tests of the ΛCDM model using simulated datasets, considering future survey observations, and we find that genetic algorithms represent a strong technique to do model-independent tests based on stage IV surveys because of a resulting robust reconstruction.


• Petreca, Alexandra Turmina (Universidade de São Paulo, Brazil): The impact of systematic effects on the cosmic distance ladder

The Hubble constant (H₀), which quantifies the current expansion rate of the Universe, remains at the center of a major cosmological debate known as the Hubble tension – a persistent discrepancy between independent determinations of H₀. This work presents an investigation of residual systematic effects that may affect the measurement of H₀ using the cosmic distance ladder method. Observational data and synthetic samples of Cepheids and Type Ia Supernovae are employed to analyze how controlled, artificially introduced systematic deviations influence the inferred cosmological parameters.


• Reis, Christopher Dorvino (USP, Brazil): Argon/xenon-based dark matter detectors and their interactions with neutrino background

The search for dark matter, one of the greatest current cosmological mysteries, is an increasingly relevant topic as detection technologies and methods advance, in contrast with the lack of conclusive results. Liquid noble gas detectors, more specifically argon and xenon, have proven to be excellent candidates for detecting dark matter. However, with their constantly increasing sensitivity, they are beginning to detect the neutrino background, which can obscure potential dark matter interactions. This results in the need for new detection and data analysis techniques in order to overcome this barrier, known as the “neutrino fog.” In this context, I present the relevant topics, such as the cross section of coherent elastic neutrino-nucleus scattering (CEvNS), the neutrino fog and the neutrino flux at detector sites, the process the detector relies on, and the number of events expected from the neutrino fog in these detectors.


• Rodrigues, Gabriel (Observatório Nacional, Brazil): Thawing Dark Energy and Massive Neutrinos in Light of DESI

Recent analyses have shown that a dynamic dark energy modeled by the CPL parameterization of the dark energy equation of state (EoS) can ease constraints on the total neutrino mass compared to the standard $\Lambda$CDM model. This helps reconcile cosmological and particle physics measurements of $\sum m_\nu$. In this study, we investigate the robustness of this effect by assessing the extent to which the CPL assumption influences the results. We examine how alternative EoS parameterizations – such as Barboza-Alcaniz (BA), Jassal-Bagla-Padmanabhan (JBP), and a physically motivated thawing parameterization that reproduces the behavior of various scalar field models – affect estimates of $\sum m_\nu$. Although both the BA and JBP parameterizations relax the constraints similarly to the CPL model, the JBP parameterization still excludes the inverted neutrino mass hierarchy at $\sim 2.1\;\sigma$ with $\sum m_\nu < 0.096$\;eV. The thawing parameterization excludes the inverted hierarchy at $\sim 3.3\sigma$ and yields tighter constraints, comparable to those of the $\Lambda$CDM model, with $\sum m_\nu < 0.071$\;eV. Our analysis also reveals that the preference for unphysical negative neutrino masses is significantly reduced in all models considered. Finally, we show that the thawing model can be mapped into the BA and JBP $w_0$–$w_a$ parameter space, with the apparent preference for the phantom regime actually supporting quintessence (non-phantom) models.


• Rodrigues, Ricardo (Universidade Estadual de Londrina, Brazil): Testing the symmetries of the universe at sub-angular scales

In this work, we implement a numerical code written in C to obtain the Multipole Vectors (MVs) and Fréchet Vectors (FVs) from a Cosmic Microwave Background (CMB) temperature map, which allows us to test the gaussianity and isotropy in a model-independent way, since these vectors are insensitive to the angular power spectrum C ℓ . Our first tests using the four Planck pipelines showed that the FVs are more sensitive to possible temperature modulations in these maps. Furthermore, we performed simple tests of the null hypothesis using the χ 2 ℓ statistic.


• Rodrigues, Caio César (Federal University of Ceará, Brazil): The Platypus Spacetime: An Example of Gravity Without Mass

We present an explicit solution to the Einstein field equations sourced by a stress tensor with identically zero energy density. We refer to it as the “platypus metric” due to its intriguing properties. It exemplifies a key difference between Newton and Einstein gravity—while Newtonian gravity is sourced exclusively by mass, pressure alone can source relativistic gravitational fields. The platypus solution is shown to have a stable photon ring, bounded nonradial null geodesics, local conformal flatness, spatial flatness with vanishing extrinsic curvature, and most importantly, we show a new compact object in the settings of pure general relativity as a mechanism for mimicking black holes.


• Roy, Rudranil (Universidad de Tarapacá, Chile): In progress

In progress


• Rueda, Sebastián (Universidad Nacional de Colombia, Colombia): An overview of SED fitting and its application to study evolutionary stages of AGNs for future uses in estimations of cosmological parameters

Active Galactic Nuclei (AGNs) are among the most luminous persistent sources in the universe and are observable across a wide range of redshifts, making them promising candidates for cosmological studies beyond the reach of traditional standard candles. This work presents an overview of spectral energy distribution (SED) fitting techniques and their application to investigate the physical and evolutionary properties of AGNs, with the long-term goal of assessing their potential use in the estimation of cosmological parameters. By analyzing SEDs across multiple wavelength regimes—particularly UV and X-ray—it is possible to identify emission regions and luminosity correlations that are less sensitive to redshift and internal variability. This approach allows for a statistical characterization of AGN populations and offers a path to reduce dispersion in luminosity-distance relations. We discuss current challenges in modeling AGN components, such as accretion disk emission and obscuration, and highlight the importance of accurate SED fitting in distinguishing evolutionary stages. This analysis contributes to the broader effort of evaluating AGNs as viable tools for probing the expansion history of the universe and understanding discrepancies in cosmological measurements.


• Sanghavi, Joy Kaushik (University of Amsterdam, Netherlands): Simulation-Based Inference for Antenna Gain Calibration in 21 cm Cosmology

The 21 cm signal from neutral hydrogen is a key probe of the Epoch of Reionization (EoR), marking the universe’s transition from a cold, neutral state to a predominantly hot, ionised one, driven by the formation of the first stars and galaxies. Extracting this faint 21 cm signal from radio interferometric data requires precise gain calibration. However, traditional calibration methods are computationally expensive and time-intensive. More efficient calibration techniques are urgently needed with next-generation radio telescopes like the Square Kilometer Array (SKA) set to host hundreds of antennas. To address this challenge, we present a sequential simulation-based inference (SBI) approach for direction-independent gain calibration, designed to automate and accelerate the process while improving scalability and accuracy. Once a forward model is established to generate simulations—transformations of the true sky image due to antenna gain variations—neural posterior estimation (NPE) with embedding networks is employed to infer the correct gain values for multiple antennas from the joint parameter-data distribution. We leverage GPU-accelerated parallelisation to efficiently estimate the large number of gain parameters within a feasible time frame. The Bayesian framework enables robust uncertainty estimation, which traditional methods often overlook, while facilitating faster and more reliable analysis of real SKA data. Future work could extend this approach to direction-dependent gains and other systematic effects or involve validation on existing radio data. By integrating these techniques into the analysis pipeline, we can fully exploit SKA’s unprecedented sensitivity, significantly improving our ability to extract fundamental cosmological insights from large-scale observations.


• Santos, Emanuelly Da Silva (UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL, Brazil): New Constraints on Interacting Dark Energy from DESI DR2 BAO Observations

In its second data release (DR2), the Dark Energy Spectroscopic Instrument (DESI) publicly released measurements of Baryon Acoustic Oscillations (BAO) from over 13.1 million galaxies and 1.6 million quasars, covering the redshift range 0.295 ≤ z ≤ 2.330. In this work, we investigate the impact of this new dataset on dark sector interaction models, which are motivated by non-gravitational interactions between dark energy (DE) and dark matter (DM), commonly referred to as interacting dark energy models (IDE). We focus on two frameworks: the traditional IDE model and the recently proposed sign-switching Interacting model (S-IDE), aiming to derive new and robust constraints on both scenarios. After carefully selecting the sample for the joint analysis, ensuring compatibility among the data without significant tension, our main results indicate that both models can alleviate the H₀ tension, reducing it to moderate tension of approximately 2.7σ. The IDE model shows compatibility with the latest S₈ constraints from cosmic shear surveys, while the S-IDE model predicts lower values of S₈, which align with alternative perspectives on the S₈ tension. For the traditional IDE model, we derive new bounds for the coupling parameter, marking the strongest constraints to date through geometric measurements. This highlights the crucial role that supernova samples can play in refining these constraints. For the S-IDE model, we find mild evidence (approximately 2σ) for the coupling parameter, suggesting a potential interaction between DE and DM.


• Sarras, Orestis (University of Tarapaca, Chile): Title: Addressing the Strong Coupling Problem via the Method of Multiple Scales in Effective Theories of Inflation

The Strong Coupling Problem presents a central challenge in various field theories, including models of early-universe inflation and modified gravity. In my recent research, I explored this issue by applying the perturbative Method of Multiple Scales — a technique well-suited for global asymptotic analysis, particularly in systems where standard perturbation theory fails due to scale-dependence. It is focused on identifying and managing non-uniformities in perturbative expansions that arise when secular terms grow due to unrecognized multi-scale behavior. We developed a physically motivated variant of the method, emphasizing its interpretation in terms of Lorentz symmetry breaking and scale-dependent instabilities, which often signal the onset of strong coupling. The central application is to the Effective Field Theory (EFT) of Inflation, where time-dependent backgrounds can render the kinetic structure degenerate and make the cutoff scale ambiguous. We demonstrate how MMS can dynamically restore perturbative control, offering a novel framework to alleviate strong coupling by tracking the emergence of kinetic terms beyond the naive expansion. These methods have potential relevance beyond standard single-field models, and may extend to modified gravity theories that admit an EFT formulation — including teleparallel models and scalar-tensor frameworks — where background evolution can obscure the identification of healthy propagating modes. This research lays the groundwork for applying this method within broader inflationary scenarios, offering a pathway to stabilize or reinterpret strongly coupled sectors in early-universe cosmology.


• Sena Vitalino, Valdir Márcio (UNIFESP, Brazil): Aprendizado Ativo para Classificação de Supernovas Tipo Ia no LSST com Dados Simulados

O Observatório Vera C. Rubin (LSST) gerará um fluxo massivo de alertas astronômicos, distribuídos por corretores como o FINK, essenciais para a extração de insights científicos. Dado o volume de dados, o aprendizado de máquina (ML) é uma escolha natural, mas um grande desafio é o número limitado de amostras confirmadas espectroscopicamente para treinamento. Este estudo avalia o desempenho do classificador na identificação de supernovas do Tipo Ia usando dados simulados, demonstrando que o Aprendizado Ativo (AL) constrói efetivamente conjuntos de treinamento otimizados e mitiga a incompatibilidade entre amostras espectroscópicas e fotométricas — mesmo em estágios iniciais do levantamento.”


• Shao, Xiaoyun (Observatório Nacional, Brazil): Cosmological constraints from angular homogeneity scale measurements

In this paper, we obtain new measurements of the angular homogeneity scale ($\theta_H$) from the BOSS DR12 and eBOSS DR16 catalogs of Luminous Red Galaxies of the Sloan Digital Sky Survey. Considering the flat $\Lambda$CDM model, we use the $\theta_H(z)$ data to constrain the matter density parameter ($\Omega_{m0}$) and the Hubble constant ($H_{0}$). We find $H_0 = 65^{+10}_{-7}$ km s$^{-1}$ Mpc$^{-1}$ and $\Omega_{m0}>0.296$. By combining the $\theta_H$ 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 $\Omega_{m0} = 0.292^{+0.013}_{-0.015}$ ($\theta_H$ + BAO) and $H_{0}=66.8 \pm 5.4 $ km s$^{-1}$ Mpc$^{-1}$ and $\Omega_{m0}=0.331 \pm 0.018$ ($\theta_H$ + SN). We show that $\theta_H$ 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, $\theta_H$ 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 $\theta_H$ data via Monte Carlo simulations. Considering a relative error of the order of 1$\%$, we obtain competitive constraints on $\Omega_{m0}$ and $H_0$ ($\approx 5\%$ error) from the joint analysis with current SN and BAO measurements.


• Souza Dos Santos, Giulya (IAG – USP, Brazil): Searching for merging galaxy clusters: Exploring clustering algorithms to identify clusters with substructures

Identifying merging galaxy clusters in observational data requires detecting signatures that often appear as substructures in the galaxy distribution. This work presents a method based on the HDBSCAN clustering algorithm to identify substructures in systems with bimodal galaxy distributions. Using numerical simulations, we demonstrate that the method achieves a purity of 74% in selecting reliable detections and an accuracy above 90%. Our results show that this approach is effective in identifying well-defined and dynamically distinct substructures from the main cluster, selecting true detections while rejecting spurious ones.


• Trindade, Nadson/Silva (Universidade Federal da Bahia, Brazil): Modeling the Mass-Richness relationship in clusters in the IllustrisTNG simulation

Observational cosmology has gained prominence in recent decades, driven by large data surveys. In this context, galaxy clusters play a fundamental role, as they are massive, gravitationally bound structures directly related to the formation of large-scale structures in the universe. A property widely used as a mass proxy is richness, which corresponds to the count of member galaxies in a cluster. The relationship between richness and mass can be established through the richness-mass distribution. In this work, we use the IllustrisTNG simulation suite to investigate this relationship.


• Turker, Ozgen Tunc (Federal University of Espírito Santo, Brazil): Accurate Cosmological Emulator for the Lensing PDF

Gravitational lensing introduces significant distortions and magnifications in the light from distant cosmic sources due to the inhomogeneous distribution of matter in the Universe. While this phenomenon carries valuable information about the large-scale structure and the dark components of the cosmos, it also acts as a source of noise by biasing distance measurements—compromising the inference of fundamental cosmological parameters. The project Accurate Cosmological Emulator for the Lensing PDF aims to address this challenge by developing a fast, reliable emulator capable of predicting one-point lensing statistics—specifically probability distribution functions (PDFs)—across a wide range of cosmological parameters and redshifts, particularly from z \sim 0.2 to z \sim 6. Using methods such as Principal Component Analysis (PCA) and XGBoost, the emulator will replace traditional high-resolution N-body simulations with an efficient, machine learning-based tool. This will drastically reduce computational cost while maintaining high precision.

Announcement:

Application deadline: May 17, 2025 (closed)

 The schedule might be changed.

Venue: The event will be held at IFT-UNESP, located at R. Jornalista Aloysio Biondi, 120 – Barra Funda, São Paulo. The easiest way to reach us is by subway or bus, See arrival instructions here.

Accommodation: Participants whose accommodation will be provided by the institute will stay at Hotel Intercity the Universe Paulista. Hotel recommendations are available here.

Attention! Some participants in ICTP-SAIFR activities have received email from fake travel agencies asking for credit card information. All communication with participants will be made by ICTP-SAIFR staff using an e-mail “@ictp-saifr.org”. We will not send any mailings about accommodation that require a credit card number or any sort of deposit. Also, if you are staying at Hotel Intercity the Universe Paulista, please confirm with the Uber/Taxi driver that the hotel is located at Rua Pamplona 83 in Bela Vista (and not in Jardim Etelvina).

BOARDING PASS: All participants, whose travel has been provided or will be reimbursed by ICTP-SAIFR, should bring the boarding pass  upon registration. The return boarding pass (PDF, if online check-in, scan or picture, if physical) should be sent to secretary@ictp-saifr.org by e-mail.

Visa information: Nationals from several countries in Latin America and Europe are exempt from tourist visa. Nationals from Australia, Canada and USA are required to apply for a tourist visa.

Poster presentation: Participants who are presenting a poster MUST BRING A PRINTED BANNER . The banner size should be at most 1 m (width) x 1,5 m (length). We do not accept A4 or A3 paper.

Power outlets: The standard power outlet in Brazil is type N (two round pins + grounding pin). Some European devices are compatible with the Brazilian power outlets. US devices will require an adapter.