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CoCo 2o26: Cosmology in Colombia
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America/Bogota
Auditorio sede P, Quinto piso (Universidad ECCI)
Auditorio sede P, Quinto piso
Universidad ECCI
Cl. 51 #19-12, Teusaquillo, Bogotá, Cundinamarca
Alejandro Guarnizo
(Universidad Antonio Nariño),
Alexander Gallego Cadavid,
Cesar A. Valenzuela-Toledo
(Departamento de Física, Universidad del Valle),
Jhan Nicolás Martínez Lobo
(Universidad Antonio Nariño),
John Bayron Orjuela-Quintana
(UNIVERSIDAD DEL VALLE),
Juan Pablo Beltran
(Universidad Nacional de Colombia),
Leonardo Castañeda Colorado
(Universidad Nacional de Colombia),
Luz Ángela García
(Universidad ECCI),
Yeinzon Rodríguez García
Description
The Eighth CoCo Meeting (Cosmology in Colombia) will be held on November 5–6, 2026, at Universidad ECCI, Bogotá, Colombia.
The goal of this meeting is to bring together cosmologists to discuss the current state of cosmology at the interface of theory and observations.
The main topics include:
The goal of this meeting is to bring together cosmologists to discuss the current state of cosmology at the interface of theory and observations.
The main topics include:
- Inflation and the early Universe,
- Cosmic microwave background,
- Large-scale structures of the Universe,
- Dark matter and neutrino astrophysics,
- Dark energy and modified gravity,
- Gravitational waves and multi-messenger astronomy.
We expect this event to provide a platform for maximizing interactions and creating new collaborations.
In-person conference: The workshop will be held in Bogotá (Colombia).
Participants
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08:15
Registration and welcome
Registration and welcome
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1
Metric Affine Lovelock's theorem
Lovelock’s hypotheses are a set of reasonable conditions one can impose on the gravitational action that hugely narrow the set of possible gravity theories. In four dimensions, and for a Lorentzian space-time manifold, the set of gravity theories reduces to just one: General Relativity. This incarnation of the Ockham’s razor philosophy has influenced in one way or another the research on the foundations of gravity and modified gravity theories for over fifty years. One of the hypotheses, not explicitly declared as such by Lovelock, is that the space-time manifold is Riemannian. In this work, we have extended Lovelock’s work to spacetimes that enjoy an affine structure fully independent of the metric one, i.e., to spacetimes that not only exhibit curvature but also torsion and non metricity. We fully recover Lovelock’s results as well as Mardones and Zanelli’s torsionful extension of Lovelock’s work in the appropriate limits. Furthermore, our results indicate that, in four dimensions, torsion and non-metricity do not propagate as independent dynamical degrees of freedom, leaving only two propagating degrees of freedom.
Speaker: Jhan Nicolás Martínez Lobo (Universidad Industrial de Santander) -
2
Phase-Space Constraints on a General Class of Eckart-like viscous Cosmologies
We study the cosmological dynamics of a general class of models where bulk viscosity is a property of dark matter using a dynamical system analysis. These viscous cosmologies are characterized by a dimensionless bulk viscous pressure given by $\Omega_\Pi = \Omega_\Pi(\Omega_m)$, where $\Omega_m$ is the matter density parameter. This phase-space analysis suggests that, in an Eckart framework, a viable early radiation era requires the complete absence of viscosity, while a proper matter-dominated epoch demands a highly sub-dominant viscous pressure. Therefore, the background cosmology must closely track the standard $\Lambda$CDM evolution and the only physically admissible late-time attractor is the cosmological constant-dominated fixed point; arguments in this paper suggest that this behaviour could be extended to a truncated Israel-Stewart theory. These constraints are validated numerically using the power-law parametrization $\Omega_\Pi = -\hat{\xi}_0 \Omega_m^s$ where $\hat{\xi}_0$ and $s$ are real parameters. For $s \geq 1$ and $\hat{\xi}_0 \ll 1$, the background reproduces $\Lambda$CDM while, for $s < 1$, the system encounters a past-time integration boundary where the dark matter density transitions into negative values and its viscous pressure evaluates to nonphysical complex numbers, disrupting the standard expansion history. Because the background expansion essentially duplicates $\Lambda$CDM, the model is unlikely to resolve the $H_0$ tension; however, linear sub-horizon perturbations evaluated under the quasi-static approximation reveal that the bulk viscosity causes a scale-dependent dissipative drag. This increases the Hubble friction, offering a possible channel to suppress structure growth and alleviate the $\sigma_8$ (or $S_8$) tension; however, a detailed scale-by-scale analysis is needed to know its imprint on the matter power spectrum.
Speaker: David Ricardo Moreno Diaz (Universidad Industrial de Santander) -
3
Recalibrating the L-σ Relation for HII Galaxies and Independent H0
We recalibrate the anchor sample of the L–σ relation for HII Galaxies (HIIG), an independent three-rung distance estimator that uses Giant Extragalactic HII Regions (GEHR) as local anchors. GEHR and HIIG are blue massive starburst systems that exhibit a seemingly ubiquitous correlation between their H-beta (Balmer) luminosity and their spectroscopic velocity dispersion, known as the L-σ relation. Although the L–σ method is very promising, particularly given the redshift range it expands to (z ~ 7), its systematic error budget remains much less explored than that of the SN Ia method. Using a hierarchical Bayesian framework on 32 homogenized host-galaxy distance moduli (Cepheid and TRGB, 26 yr of NED literature), we find H0 = 74.1 +/- 3.8 km/s/Mpc with Cepheid anchors (consistent with SH0ES) and H0 = 67.3 +/- 3.8 km/s/Mpc with TRGB anchors (consistent with Planck and CCHP). The joint fit yields h = 0.721 +/- 0.039. This anchor-dependent split could suggest part of the Hubble tension may trace back to systematics within the distance ladder itself, rather than to new physics alone.
Speaker: Holman Quintero-Salazar (Universidad de Guanajuato) -
11:00
Coffe break
Coffee break
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4
Beyond zero-temperature: moduli fields, thermal corrections and dark matter production
Early matter-dominated epochs and non-standard cosmological scenarios are frequently motivated by top-down constructions and UV completions of beyond-Standard Model physics. Scalar fields, as natural extensions to the Standard Model of particles, provide a well-studied framework for exploring deviations from the concordance cosmological model and might play a crucial role in dark matter production - whether through direct decays or modifications to the universe's thermal history. Notably, moduli fields, ubiquitous in supergravity and superstring models, develop finite-temperature corrections to their dynamics, leading to significant cosmological imprints despite never reaching thermal equilibrium. In this talk, we review the general dynamics of scalar fields in cosmology, including finite-temperature effects, and present preliminary results derived from modified Boltzmann equations. By implementing numerical solutions for a toy model of direct production, we explicitly contrast the zero-temperature and finite-temperature regimes, highlighting their phenomenological implications.
Speaker: Diego Gallego (Universidad Pedagógica y Tecnológica de Colombia.) -
5
Complexity of Black Hole Microstate Geometries
A central question in quantum gravity is how the entropy of a black hole arises from its microstates. In string theory, individual microstates of D1-D5-P black holes are described by smooth, horizonless geometries known as superstrata, and holographic complexity offers a new tool to probe how these states differ from the black hole they build.
We compute the volume complexity (CV) of formation, relative to empty AdS, for the $(1,0,n)$, $(2,1,n)$ and $(2,0,n)$ superstratum families, in both their full 6D geometry and their 3D reduction. We obtain the complexity as a function of the rescaled microstate parameter $\hat{b}$ and the mode number $n$, together with its large-$n$ scaling.
Unlike BTZ, the microstate complexity is time-independent. In the supertube limit it is negative, so the microstate is simpler than the vacuum. The 3D and 6D prescriptions agree at leading order but differ at finite order, pointing to possible ambiguities in defining volume complexity in higher-dimensional embeddings.
Speaker: Sebastián Moreno Chalacá (Universidad del Valle) -
12:20
Lunch break
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6
Cosmology Cartography: estimación de redshift por píxel en imágenes HSC-SSP mediante redes U-Net
Los redshifts fotométricos suelen estimarse objeto por objeto, a partir de catálogos que dependen de la detección y segmentación previa de fuentes. En este trabajo se presenta un enfoque alternativo que predice el redshift directamente a nivel de píxel a partir de imágenes multibanda, con el fin de construir mapas densos de redshift del cielo. Para ese objetivo se utilizó zscrape, un pipeline que toma, normaliza y desduplica catálogos espectroscópicos y fotométricos de decenas de surveys. El resultado es un catálogo unificado en formato HATS de aproximadamente 1.160 millones de fuentes, que le asigna a cada redshift un peso de calidad (wspec) calibrado por consenso entre catálogos. A partir de él se genera mapas con su respectivas etiquetas (redshift) para más de 1.500 patches de HSC-SSP PDR3 (Deep+UltraDeep) en las bandas grizy, con unos 12,5 millones de fuentes etiquetadas. Se entrena una red U-Net sobre estos datos y se explora distintas normalizaciones, esquemas de pérdida ponderados por la calidad del redshift y estrategias de data augmentation. Finalmente el estado del proyecto se encuentra en abordar el problema como uno de clasificación sobre bins de redshift (y no un problema de regresión), lo que permite predecir una función de densidad de probabilidad completa en cada píxel en lugar de un valor puntual. Se discute el estado actual del proyecto, las dificultades asociadas a la escasez de redshifts espectroscópicos a alto z, y las perspectivas de extender el método hacia la predicción de un campo continuo de densidad de fuentes en el espacio (z, x, y).
El trabajo fue realizado en el marco de la pasantía Mitacs Globalink en University of Victoria (Uvic).
Speaker: Juan Camilo Sanchez Tovar (Universidad Nacional de Colombia) -
7
Systematic tracking of linear cosmological perturbations beyond the standard quasi-static approximation in Horndeski gravity.
The quasi-static (QSA) and sub-horizon (SHA) approximations are standard tools used to simplify the complex dynamics of linear cosmological perturbations in modified gravity. However, their conventional implementation relies on an ad-hoc truncation of time derivatives, which obscures theoretical errors and inadvertently eliminates fundamental background dynamics. In this work, we propose a mathematically rigorous framework that elevates the QSA and SHA from heuristic truncations to controlled asymptotic expansions within the broad class of Horndeski scalar-tensor theories. By introducing a set of dimensionless tracking parameters driven by the spatial ratio $\varepsilon = aH/k$, we formulate an exact rewriting of the perturbation equations where the standard QSA/SHA emerges purely as a well-defined zeroth-order asymptotic limit. Our systematic approach explicitly tracks higher-order dynamical corrections and reveals that the standard approach spuriously intertwines spatial scales with unexpanded temporal derivatives. To determine the physical regime where this expansion is strictly valid, we introduce a deep-matter tracking parameter, defining a clear validity window for the formalism. We evaluate the dynamical convergence of our $\mathcal{O}(\varepsilon^2)$ expansion by comparing it against the standard approach and the full unapproximated system using the Designer Horndeski (HDES) model as a case study. We find that our systematic expansion significantly improves accuracy over the standard approach, robustly tracking the exact evolution of the gravitational potentials and the effective dark energy fluid variables.
Speaker: SANTIAGO GARCIA SERNA -
8
Rapid Black Hole Growth in the Early Universe
The discovery of quasars and their supermassive black holes (SMBHs) over $10^{9}$ $M_{\odot}$ merely hundreds of millions of years after the Big Bang generates tension with the idea of Eddington-limited accretion and pressures the community into exploring the concept of massive black hole seeds and/or super-Eddington accretion. The observation that many black holes have reached supermassive status while obeying the Eddington limit is puzzling, as accretion models are not spherically symmetric. We address this issue by illustrating the physics behind a picture of inner disk accretion involving a geometrically thick, hot quasi-spherical flow, and argue that such an inner region provides the radiation that instantiates the Eddington limit. Given the energetics of the inner disk edge, we show how the characteristic electron cross section drops below its Thomson value, allowing black holes to grow rapidly despite being Eddington-limited. Indeed, after implementing a modified cross section calculated via the Klein─Nishina formula, we find that SMBH formation time drops by up to 47$\%$. In this context, we show how a $10^{9}$ $M_{\odot}$ black hole can form from a seed 10 $M_{\odot}$ black hole within 500 Myr by way of accretion and mergers. While our picture is oversimplified and contrived in a number of ways that we discuss, we suggest that our scenario is interesting in that it offers a solution to two issues at the intersection of astrophysics and cosmology, namely the reason the Eddington limit is obeyed and how some black holes have grown rapidly despite that limit.
Reference
How a Klein–Nishina Modified Eddington-limited Accretion Explains Rapid Black Hole Growth in the Early Universe, Jackson Frangos, Erick Rosen, Michael Williams, Chandra B. Singh, David Garofalo, The Astrophysical Journal, 989, 197.Speaker: Dr Chandra B. Singh -
15:30
Coffee break
Coffee break
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9
Jacobson's Thermodynamic Approach to Classical Gravity Applied to Non-Riemannian Geometries: Remarks on the Simplicity of Nature
Three decades ago, Ted Jacobson surprised us with a very appealing approach to classical gravity. According to him, the gravitational field equations are the consequence of the first law of thermodynamics applied to a Rindler observer. Jacobson’s approach, being formulated for Riemannian geometries, we have wondered what its consequences would be for non-Riemannian geometries. The results of our quest have been particularly appealing: we have found that the theory that derives from the Einstein- Hilbert action, arguably “the simplest one,” does not belong to the pool of gravitational theories available for Nature’s selection (except in the Riemannian case). In the search for a unique alternative, we have considered the hypotheses employed in the formulation of the Lanczos-Lovelock theories of gravity. Together, the two approaches point toward the theory that derives from the Einstein-Hilbert action plus a term quadratic in the torsion vector as the one that would be selected by Nature in the non- Riemannian case without non-metricity (when the energy-momentum tensor is identified as its metric version). The same strategy cannot be followed in the full non-Riemannian case (and in the previous case when the energy-momentum tensor is identified as its canonical version) as the two approaches are mutually inconsistent.
Speaker: Yeinzon Rodríguez García -
10
A Critique on Formulating Local Theories of Gravity from Non-Extensive Entropies
The thermodynamic emergence of local spacetime dynamics is inextricably tied to the strict extensivity of the holographic area law. While quantum gravity candidates often motivate generalized, non-extensive entropy-area relations for black holes, substituting these into Jacobson's framework to derive modified gravity theories is generically inconsistent. We argue that any departure from holographic extensivity introduces long-range correlations that destroy local spacetime causality. Consequently, the resulting macroscopic theories inevitably violate the Equivalence Principle, break diffeomorphism invariance, or exhibit overt acausality. We conclude that an extensive area law is a necessary condition for consistent local gravitational dynamics.
Speaker: JOHN BAYRON ORJUELA-QUINTANA (UNIVERSIDAD DEL VALLE) -
11
Anisotropic Universes in Light of Background Observations
Although $\Lambda$CDM remains the standard cosmological model, outstanding observational and theoretical challenges motivate the exploration of alternative scenarios. Among these are models in which an anisotropic dark energy component breaks cosmic isotropy. In this talk, we investigate four classes of anisotropic dark energy models: a scalar field coupled to a vector field, a scalar field coupled to a 2-form field, scalar fields with an internal symmetry, and an inhomogeneous scalar field. We confront these models with background observations to constrain the present-day anisotropy of the cosmic expansion. Our results show that observations strongly favor the isotropic limit in all models except the scalar field coupled to a 2-form field, for which the isotropic limit is disfavored.
Speaker: Mr Jose Palacios-Cordoba (Universidad del Valle) -
12
Viabilidad cosmológica de formalismos de entropía no extensiva en el marco de la gravedad termodinámica
La conjetura de la gravedad termodinámica establece que las ecuaciones de campo de la relatividad general pueden derivarse a partir de relaciones termodinámicas aplicadas al horizonte cosmológico. En este marco, la primera ley de la termodinámica aplicada al horizonte aparente de un universo plano y homogéneo descrito por la métrica FLRW permite obtener ecuaciones de Friedmann modificadas cuya forma depende directamente de la relación entropía-área adoptada. Se estudia sistemáticamente el impacto cosmológico de cuatro entropías no extensivas ampliamente discutidas en la literatura: Tsallis, Rényi, Sharma-Mittal y Kaniadakis. Para cada formulación se derivan las ecuaciones de Friedmann modificadas y se determina el rango de parámetros entrópicos que garantiza una cosmología físicamente viable, exigiendo la positividad de los parámetros de densidad de energía, la reproducción de la secuencia estándar de dominación por radiación, materia y energía oscura, y la concordancia con el valor observado del parámetro de Hubble. Se presentan resultados para la evolución del parámetro de desaceleración, los parámetros de densidad y la ecuación de estado de la energía oscura efectiva, evidenciando cómo cada entropía generalizada describe de manera diferenciada las distintas etapas de la evolución cósmica.
Speaker: Mr PEDRO MARTIN IBARBO PERLAZA (Universidad del Valle)
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08:15
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13
Master equation solutions in the linear regime of characteristic formulation of general relativity in the Minkowski and Schwarzschild Backgrounds
From the field equations in the linear regime of the characteristic formulation of general relativity, Bishop, for a Schwarzschild’s background, and Mädler, for a Minkowski’s background, were able to show that it is possible to derive a fourth order ordinary differential equation, called master equation, for the J metric variable of the Bondi-Sachs metric. Once β, another Bondi-Sachs potential, is obtained from the field equations, and J is obtained from the master equation, the other metric variables are solved integrating directly the rest of the field equations. In the past, the master equation was solved for the first multipolar terms, for both the Minkowski’s and Schwarzschild’s backgrounds. Also, Mädler recently reported a generalisation of the exact solutions to the linearised field equations when a Minkowski’s background is considered, expressing the master equation family of solutions for the vacuum in terms of Bessel’s functions of the first and the second kind. Here, we report new solutions to the master equation for any multipolar moment l, with and without matter sources in terms only of the first kind Bessel’s functions for the Minkowski, and in terms of the Confluent Heun’s functions (Generalised Hypergeometric) for radiative (nonradiative) case in the Schwarzschild’s background. We particularize our families of solutions for the known cases for l=2 reported previously in the literature and find complete agreement, showing the robustness of our results. Finally, we apply this formalism to a binary point particle system, obtaining the Peters and Mathews gravitational radiation formula.
Speaker: Dr Carlos Eduardo Cedeño Montaña (Universidad Santiago de Cali) -
14
Physics-Informed Neural Networks for solving cosmological background equations in standard and extended cosmological models
Modern cosmology is grounded in the solution of the cosmological background equations, a system of differential equations obtained by applying Einstein’s field equations to a homogeneous and isotropic Universe. These equations describe the large-scale evolution of the Universe and form the basis of modern cosmological models and the interpretation of observational data. Although analytical solutions exist for simplified scenarios, the inclusion of additional components, such as massive neutrinos and dynamical dark energy parametrizations, enlarges the cosmological parameter space and requires numerical methods to obtain accurate solutions. In recent years, Physics-Informed Neural Networks (PINNs) have emerged as an alternative approach for solving differential equations by incorporating the governing physical laws into the training process. This work proposes the use of PINNs to solve the background equations for the standard ΛCDM model and parametric dark energy models described by the Chevallier-Polarski-Linder (CPL), Jassal-Bagla-Padmanabhan (JBP), and Barboza-Alcaniz (BA) equation-of-state parametrizations, evaluating their performance in scenarios with a higher-dimensional parameter space by the inclusion of neutrinos and dynamical dark energy. The methodology will be validated through comparison of the predicted solutions with analytical and numerical solutions, using approximation error and computational cost as performance metrics. The expected outcome is a precise and computationally efficient framework for solving cosmological background equations, providing an alternative computational method for the study of both standard and extended cosmological models. Finally, since the temporal evolution of the Universe follows an inherently causal structure, where the state of the system at a given epoch depends on its state at earlier times, we discuss how incorporating causality into the PINNs framework affects convergence, accuracy, and computational efficiency in solving the cosmological background equations.
Speaker: Angeline Jolie Betancourt Beltran (Universidad el Bosque) -
15
A Photometric AGN Golden Sample for High-Redshift Cosmology: Extending the Hubble Diagram Beyond Type Ia Supernovae
Active Galactic Nuclei (AGNs) are among the few astrophysical populations capable of probing the expansion history of the Universe beyond the redshift range currently accessible to Type Ia supernovae. We investigate their cosmological potential through an analysis of more than $5\times10^{5}$ quasars from the SDSS DR14 catalog spanning redshifts up to $z\sim3.5$. The ultraviolet--X-ray luminosity relation is examined in multiple redshift intervals using independent linear regressions. We obtain slopes in the range $\gamma \simeq 0.59$--$0.61$ and a nearly constant dispersion of $\sigma_{\rm rms}\simeq0.30$ dex, with no statistically significant evidence for redshift evolution. These results support the use of AGNs as high-redshift cosmological tracers. Building on this framework, we develop a multidimensional selection methodology combining photometric, statistical, and cosmological-consistency criteria to identify a photometric AGN golden sample of 255 candidates from SDSS DR17. These sources are incorporated into a joint Type Ia supernova--AGN Hubble diagram, extending the cosmological reconstruction beyond the regime densely populated by supernova observations. The resulting analysis provides a complementary determination of the Hubble constant and enables direct comparisons with contemporary cosmological constraints.
Speaker: Sebastian Rueda Blanco (Universidad Nacional de Colombia) -
11:00
Coffee break
Coffee break
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16
Spin bundles and Dirac equation in FRW metric
In this work we construct a fiber bundle for Dirac spinors associated with the orthogonal frame bundle using a spinorial representation of the Lorentz group. From this geometric framework, we derive an expression for the spin connection and formulate the general covariant Dirac equation in curved spacetime (gravitational background). Finally, we specialize to a FRW metric in conformal time to get the Dirac equation in an expanding universe.
Speakers: Daniel Barrera (Universidad Nacional de Colombia - Sede Bogotá), David García Prieto (Universidad Nacional de Colombia) -
17
Semi-Analytical Jeans Filtering Functions for Baryonic Density and Velocity Fields in Second-Order Cosmological Perturbation Theory
Cosmological perturbation theory provides the fundamental framework for
describing the evolution of the matter-energy density field in an expanding Universe and serves as the basis for understanding the formation of large-scale structures within the ΛCDM paradigm. In this work, we present a semi-analytical approach to describe the evolution of fluctuations —small deviations from the mean density— in a mixed fluid composed of cold dark matter (CDM) and baryonic matter. Assuming that the Universe is governed by General Relativity (GR), we employ the Vlasov equation to derive the general equations of motion for this mixed cosmological fluid, incorporating baryonic effects through the stress tensor by considering only the contributions from baryonic pressure. We then introduce the Jeans Filtering Functions (JFF) as a biasing tool that allows us to describe baryonic fluctuations with CDM as a tracer, and obtain an semi-analytical description of the fluctuations —a novel and uncommon approach compared to the accepted computational advances currently available in this field. First- and second-order solutions are obtained using an semi-analytical method based on a single iteration of the equations of motion. These solutions can be evaluated at low computational cost to study the behavior of the filtering scale at second order relative to the linear case and its impact on the matter power spectrum, without computing it explicitly. Unlike previous works, which evaluate these effects at the level of the power spectrum, we rely solely on the fluctuation fields to quantify the impact of baryonic matter on the matter power spectrum. Specifically, we obtain semi-analytical expressions for baryonic fluctuations in the density and velocity fields, with our most significant result concerning to the velocity divergence field. These semi-analytical results represent a main contribution of this work, are readily evaluable, and provide valuable physical insight into the role of baryons in the large-scale structure (LSS) of the Universe. They also reveal how pressure effects shift the filtering scale and how the inclusion of this component could influence parameters such as the filtering mass and the temperature of pressure-supported components.Speaker: Diego Fernando Fonseca Moreno (Universidad Nacional de Colombia/Universidad Antonio Nariño) -
12:20
Lunch break
Lunch break
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18
Perturbative vacuum constraints in higher-curvature gravity: Schwarzschild deformations and strong-field observables
Understanding how higher-order curvature corrections modify black hole spacetimes is essential for exploring possible deviations from General Relativity in the strong-field regime. In this work, we investigate the gravitational effects of a power-law Gauss–Bonnet modification in four dimensions, focusing on the perturbative structure of static, spherically symmetric vacuum solutions. Starting from a general gravitational Lagrangian containing quadratic curvature invariants, we develop a first-order perturbative framework around the Schwarzschild geometry and identify the conditions under which genuinely new gravitational contributions arise.
We consider a family of models characterized by the interaction $\Psi_\eta=\ell_\lambda^{4\eta-2}\mathcal G^\eta$, where $\mathcal G$ denotes the Gauss–Bonnet invariant. Unlike Ricci-based modifications, which preserve the vacuum Einstein solutions along the analytic perturbative branch, these nonlinear curvature interactions can generate nontrivial corrections to the Schwarzschild metric. We obtain explicit analytical expressions for the metric perturbations and examine their implications for several characteristic properties of black holes, including the event horizon, innermost stable circular orbit, photon sphere, gravitational shadow, Hawking temperature, and Wald entropy.
Our results reveal a distinctive dependence on the exponent $\eta$. Within the asymptotically controlled regime (\eta>2/3), positive perturbative couplings produce an increase in the characteristic horizon and orbital radii for $2/3<\eta<1$, while the opposite behavior occurs for $\eta>1$. The special case $\eta=1$ recovers the Schwarzschild geometry, reflecting the topological character of the linear Gauss–Bonnet term in four dimensions, although a constant contribution to the entropy remains. We also explore how shadow measurements can provide sensitivity to these modifications, illustrating the potential relevance of black hole imaging for testing higher-curvature gravitational models.
These findings provide an analytical connection between the mathematical structure of modified gravity theories and potentially measurable strong-field phenomena, offering a framework for investigating departures from Einstein gravity through black hole observations.
Speaker: Daniel Molano (Universidad de los Andes) -
19
A Geometric Approach to the Quantization of Gauged Nonlinear Sigma Models
We present a geometric approach to the quantization of gauged nonlinear sigma models associated with the symmetry-breaking pattern $O(N+1)\to O(N)$, whose Goldstone fields parametrize the sphere $S^N\simeq O(N+1)/O(N)$. Starting from the linear sigma model, we describe the resulting nonlinear theory and gauge its $O(N)$ subgroup using Killing vector fields and differential forms on $S^N$. This construction connects the classical gauge structure with BRST quantization, making explicit how the BRST charge and its nilpotency reflect the underlying symmetry geometry. Finally, we outline potential applications to scalar and topological dark matter models, with implications for cosmology and astrophysics.
Speaker: Andrés Fernando Castillo Ramirez (Universidad Antonio Nariño) -
20
Pauli blocking mechanism in the stability of scalar dark matter in the expanding universe
We present a study of the cosmic stability of a scalar dark matter candidate coupled to a pair of Majorana fermions using the Boltzmann equations. We incorporate quantum interactions, such as decay and annihilation processes into the evolution of the number and energy densities of this dark matter model. By numerically solving the system of coupled differential equations while considering full fermion and boson statistical factors, we show that the Pauli exclusion principle (or Pauli blocking) can extend the cosmic lifetime of this dark matter particle beyond the age of the universe. Additionally, in contrast to traditional decaying dark matter models that require extremely light masses to achieve such stability, this scenario allows for more reasonable mass values.
Speaker: Cristian Eduardo Martínez Torres -
15:30
Coffee break
Coffee break
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21
Producción cosmológica gravitacional de partículas escalares en un fondo inflacionario de tipo ‘‘rapid-turn’’.
La producción cosmológica gravitacional es conocida como el efecto de creación de partículas de un campo cuántico sobre un universo en expansión debida únicamente a la interacción gravitacional. Durante la fase de expansión acelerada del universo, un campo cuántico presenta excitaciones agresivas que modifican la forma en como crea y destruye partículas. Dado que el campo evoluciona desde un estado de vacío bien definido, pasadas las fases de inflación y reheating, el campo tiene una
nueva representación con un nuevo vacío cuántico bien definido, lo que se interpreta como creación de partículas. Estas partículas creadas pueden jugar un rol importante en varias observables a lo largo de la evolución del universo, tales como la densidad reliquia de materia oscura, radiación de ondas gravitacionales, la asimetría bariónica entre otras.Por otro lado, el auge de las teorías inflacionarias que proponen multicampos para dirigir la expansión acelerada del universo ha generado interés por su capacidad para modelar etapas tempranas del universo con nuevos grados libertad, generar nuevos resultados que pueden probarse con los últimos datos obtenidos de los diferentes observatorios, y adaptarse a teorías de gravedad cuántica.
En este trabajo se presenta un estudio sobre la producción cosmológica gravitacional de partículas de un campo cuántico escalar aplicada sobre un fondo inflacionario de multicampos de tipo ‘‘rapid-turn’’ donde el momento angular de los campos inflacionarios no es conservado. El mecanismo de ‘‘rapidturn’’ genera dinámicas en la evolución del espacio-tiempo que presentan inestabilidades en la curvatura y, por ende, modifican la densidad de partículas creadas debido a la excitación del campo cuántico por interacción gravitacional durante las fases de inflación y reheating. Estudiando los diferentes escenarios de evolución (variando las condiciones iniciales del sistema inflacionario), se pueden analizar las densidades reliquia creadas de partículas escalares y concluir en cuales escenarios esta densidad reliquia predicha por la teoría puede explicar la densidad reliquia de materia oscura en
el universo.Speaker: Diego Nicolás Ordóñez Peña (Universidad Nacional de Colombia) -
22
Self-interacting p-forms and the shear-free anisotropic cosmological model
The cosmological principle demands statistical homogeneity and isotropy at large enough scales. Although this principle is firmly based on observations, the cosmological principle perhaps requires more than what is actually necessary, the latter being just isotropic expansion with no vorticity. This rationale has led to the formulation of what is called extended Friedmann-Lemaitre-Robertson-Walker (eFLRW) cosmologies; these make a class of irrotational cosmologies that dynamically evolve like the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies, simultaneously possessing non-vanishing anisotropic spatial curvature and anisotropic stress that balance each other while the shear vanishes. Thorsrud and others thoroughly investigated such scenarios in the case of an action built from free differential p-forms. In this paper, we extend known results by incorporating gauge theories and self interactions in the search for a more realistic description of the universe. We have found that the non-free 3-form case, where the potential is the sum of a constant term and a quadratic term in the 3 form, and where the latter is not charged under any non-Abelian Lie group, is the only non-trivial circumstance where the shear-free cosmology described above is realized.
Speaker: Yeinzon Rodríguez García -
16:50
Closure and final words
Closure and final words
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13