arXiv subjects

Carlos Maldonado

Publications and source records attributed to Carlos Maldonado.

14 recordsLinked to original sources

arXiv2026

WIMP Freeze-Out in Diffusive Unimodular Gravity

We study a non-standard cosmology (NSC) scenario within the Unimodular Gravity (UG) framework, sourced by a scalar field $\phi$ that undergoes energy diffusion, parametrized by the diffusion parameter $x$, the initial energy densities rate $\kappa\equiv\rho_\phi/\rho_\gamma|_{\text{ini}}$, and the end-of-domination temperature $T_{\text{end}}$. We compare this UG+NSC scenario with standard NSC and $\Lambda$CDM cosmologies for WIMP Dark Matter (DM) production via the freeze-out mechanism. We find that energy diffusion reshapes the allowed $(m_\chi, \langle\sigma v\rangle)$ parameter space, where $m_\chi$ is the DM mass and $\langle \sigma v \rangle$ is the thermally averaged annihilation cross section, opening regions otherwise excluded by DM overproduction in $\Lambda$CDM, and shifting the mass and cross-section ranges accessible to WIMP candidates depending on $x$, $\kappa$, $T_{\text{end}}$, and the barotropic index $\omega$ of $\phi$. As a concrete application, we implement this framework for the Real Singlet Scalar WIMP and test its $(m_\chi, \lambda_{HS})$ parameter space against current direct detection bounds from the LZ experiment, showing that energy diffusion opens previously unconstrained regions in the Higgs-portal coupling $\lambda_{HS}$ and thereby alters the detectability prospects of this benchmark model in future searches.

hep-ph↗

arXiv2026

Ionospheric Observations from the ISS: Overcoming Noise Challenges in Signal Extraction

The Electric Propulsion Electrostatic Analyzer Experiment (ÈPÈE) is a compact ion energy bandpass filter deployed on the International Space Station (ISS) in March 2023 and providing continuous measurements through April 2024. This period coincides with the Solar Cycle 25 maximum, capturing unique observations of solar activity extremes in the mid- to low-latitude regions of the topside ionosphere. From these in situ spectra we derive plasma parameters that inform space-weather impacts on satellite navigation and radio communication. We present a statistical processing pipeline for ÈPÈE that (i) estimates the instrument noise floor, (ii) accounts for irregular temporal sampling, and (iii) extracts ionospheric signals. Rather than discarding noisy data, the method learns a baseline noise model and fits the measurement surface using a scaled Vecchia Gaussian process approximation, recovering values typically rejected by thresholding. The resulting products increase data coverage and enable noise-assisted monitoring of ionospheric variability.

physics.space-ph↗

arXiv2025

A Systematic Literature Review of Machine Learning Techniques for Observational Constraints in Cosmology

This paper presents a systematic literature review focusing on the application of machine learning techniques for deriving observational constraints in cosmology. The goal is to evaluate and synthesize existing research to identify effective methodologies, highlight gaps, and propose future research directions. Our review identifies several key findings: (1) various machine learning techniques, including Bayesian neural networks, Gaussian processes, and deep learning models, have been applied to cosmological data analysis, improving parameter estimation and handling large datasets. However, models achieving significant computational speedups often exhibit worse confidence regions compared to traditional methods, emphasizing the need for future research to enhance both efficiency and measurement precision. (2) Traditional cosmological methods, such as those using Type Ia Supernovae, baryon acoustic oscillations, and cosmic microwave background data, remain fundamental, but most studies focus narrowly on specific datasets. We recommend broader dataset usage to fully validate alternative cosmological models. (3) The reviewed studies mainly address the $H_0$ tension, leaving other cosmological challenges-such as the cosmological constant problem, warm dark matter, phantom dark energy, and others-unexplored. (4) Hybrid methodologies combining machine learning with Markov chain Monte Carlo offer promising results, particularly when machine learning techniques are used to solve differential equations, such as Einstein Boltzmann solvers, as prior to Markov chain Monte Carlo models, accelerating computations while maintaining precision. (5) There is a significant need for standardized evaluation criteria and methodologies, as variability in training processes and experimental setups complicates result comparability and reproducibility (abridged).

astro-ph.CO↗

arXiv2025

FIMP Dark Matter in bulk viscous non-standard cosmologies

In this paper, we revisit the extension of the classical non-standard cosmological model in which dissipative processes are considered through a bulk viscous term in the new field $ϕ$, which interacts with the radiation component during the early universe. Specifically, we consider an interaction term of the form $Γ_ϕ ρ_ϕ$, where $Γ_ϕ$ represents the decay rate of the field and $ρ_ϕ$ denotes its energy density and a bulk viscosity described by $ξ=ξ_{0}ρ_ϕ^{1/2}$, within the framework of Eckart's theory. This extended non-standard cosmology is employed to explore the parameter space for the production of Feebly Interacting Massive Particles (FIMPs) as Dark Matter candidates, assuming a constant thermal averaged Dark Matter production cross-section ($\langleσv\rangle$), as well as a preliminary analysis of the non-constant case. In particular, for certain combinations of the model and Dark Matter parameters, namely ($T_\text{end}$,$κ$) and $(m_χ,\langleσv\rangle)$, where $T_\text{end}$ corresponds to the temperature at which $ϕ$ decays, $κ$ is the ratio between the initial energy density of $ϕ$ and radiation, and $m_χ$ is the Dark Matter mass, we identify extensive new parameter regions where Dark Matter can be successfully established while reproducing the currently observed relic density, in contrast to the predictions of $Λ$CDM and classical non-standard cosmological scenarios.

hep-ph↗

arXiv2024

WIMP dark matter in bulk viscous non-standard cosmologies

In this paper, we explored an extension of the classical non-standard cosmological scenario in which the new field, $ϕ$, which interacts with the radiation component in the early universe, experiences dissipative processes in the form of a bulk viscosity. Assuming an interaction term given by $Γ_ϕρ_ϕ$, where $Γ_ϕ$ accounts for the decay rate of the field and $ρ_ϕ$ corresponds to its energy density, and a bulk viscosity according to the expression $ξ=ξ_{0}ρ_ϕ^{1/2}$ in the framework of Eckart's theory, we apply this novel non-standard cosmology to study the parameters space for WIMPs Dark Matter candidate production. This parameter space shows deviations from the classical non-standard cosmological scenario, obtaining new regions to search for this candidate. In particular, for certain combinations of the free parameters, we found large regions in which the model can establish the DM and reproduce the current observable relic density.

hep-ph↗

arXiv2023

Dark Matter in a bi-metric universe

We study the possibility to describe dark matter in a model of the universe with two scale factors and a non-standard Poisson bracket structure characterized by the deformation parameter κ. The dark matter evolution is analyzed in the early stages of the universe, and its relic density is obtained via the Freeze-In and Freeze-Out mechanism. We show that by fixing \k{appa} and the initial ratio of energy densities present in the different sectors of the universe, the space of thermal average annihilation cross-sections and dark matter masses compatible with the standard cosmology prior to Big Bang Nucleosynthesis (BBN), is enlarged. This feature of the model is compatible with non-standard cosmology.

hep-ph↗

arXiv2021

New opportunities for axion dark matter searches in nonstandard cosmological models

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology. Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $ϕ$ described by a general equation of state $ω$. The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window. This is the case for kination, or in general for scenarios with $ω> 1/3$. However, if $ω< 1/3$, as in the case of an early matter domination, the decay of $ϕ$ injects additional entropy relative to the case of the standard model, diluting this way the preexisting axion abundance, and rendering lighter axions viable. For a misalignment angle $0.5 < θ_i < π/\sqrt{3}$, the usual axion window becomes expanded to $4 \times 10^{-9}$ eV $\lesssim m_a \lesssim 2 \times 10^{-5}$ eV for the case of an early matter domination, or to $2 \times 10^{-6}$ eV $\lesssim m_a \lesssim 10^{-2}$ eV for the case of kination. Interestingly, the coupling axion-photon in such a wider range can be probed with next generation experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN. Axion dark matter searches may therefore provide a unique tool to probe the history of the universe before Big Bang nucleosynthesis.

hep-ph↗

arXiv2021

Bi-metric Universe with Matter

We analyze the early stage of evolution of a universe with two scale factors proposed in [1] when matter is present. The scale factors describe two causally disconnected patches of the universe interacting trough a non-trivial Poisson bracket structure in the momentum sector characterized by one parameter κ. We studied two scenarios in which one of the patches is always filled with relativistic matter while the other contains relativistic matter in one case, and non-relativistic matter in the second case. By solving numerically the set of equations governing the dynamics, we found that the energy content of one sector drains to the other and from here it is possible to constraint the deformation parameter κby imposing that the decay of the energy density happens, at most, at the Big Bang Nucleosynthesis temperature in order to return to the usual behavior of radiation. The relation with Non Standard Cosmologies is also addressed.

gr-qc↗

arXiv2019

Reconstructing Non-standard Cosmologies with Dark Matter

Once dark matter has been discovered and its particle physics properties have been determined, a crucial question rises concerning how it was produced in the early Universe. If its thermally averaged annihilation cross section is in the ballpark of few$\times 10^{-26}$ cm$^3$/s, the WIMP mechanism in the standard cosmological scenario (i.e. radiation dominated Universe) will be highly favored. If this is not the case one can either consider an alternative production mechanism, or a non-standard cosmology. Here we study the dark matter production in scenarios with a non-standard expansion history. Additionally, we reconstruct the possible non-standard cosmologies that could make the WIMP mechanism viable.

hep-ph↗

arXiv2019

Ultraviolet Freeze-in and Non-Standard Cosmologies

A notable feature of UV freeze-in is that the relic density is strongly dependent on the highest temperatures of the thermal bath, and a common assumption is that the relevant 'highest temperature' should be the reheating temperature after inflation $T_\text{RH}$. However, the temperature of the thermal bath can be significantly higher in certain scenarios, reaching a value denoted T max , a fact which is only apparent away from the instantaneous decay approximation. Interestingly, it has been shown that if the operators are of sufficiently high mass dimension then the dark matter abundance can be enhanced by a 'boost factor' depending on ($T_\text{max}/T_\text{RH}$) relative to naive estimates assuming instantaneous reheating. We highlight here that in non-standard cosmological histories the critical mass dimension of the operator above at which the instantaneous decay approximation breaks down, and the exponent of the boost factor, depend on the equation of state $ω$ prior to reheating. We highlight four examples in which the dark matter abundance receives a significant enhancement in the context of gravitino dark matter, the moduli portal, the Higgs portal, and the spin-2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of non-standard cosmologies.

hep-ph↗

arXiv2019

Establishing the Dark Matter Relic Density in an Era of Particle Decays

If the early universe is dominated by an energy density which evolves other than radiation-like the normal Hubble-temperature relation $H\propto T^2$ is broken and dark matter relic density calculations in this era can be significantly different. We first highlight that for a population of states $ϕ$ sourcing an initial expansion rate of the form $H\propto T^{2+n/2}$ for $n\geq-4$, during the period of appreciable $ϕ$ decays the evolution transitions to $H\propto T^4$. The decays of $ϕ$ imply a source of entropy production in the thermal bath which alters the Boltzmann equations and impacts the dark matter relic abundance. We show that the form of the initial expansion rate leaves a lasting imprint on relic densities established while $H\propto T^4$ since the value of the exponent $n$ changes the temperature evolution of the thermal bath. In particular, a dark matter relic density set via freeze-in or non-thermal production is highly sensitive to the temperature dependance of the initial expansion rate. This work generalises earlier studies which assumed initial expansion rates due to matter or kination domination.

hep-ph↗

arXiv2017

Testing a new WISP Model with Laboratory Experiments

We explore the phenomenological consequences of a model with axion-like particles and hidden photons mixing with photons. In this model, the hidden photon is directly coupled to the photon, while the axion coupling is induced by an external electromagnetic field. We consider vacuum effects on a polarised photon beam, like changes in the ellipticity and rotation angles.

hep-ph↗

arXiv2017

A two particle hidden sector and the oscillations with photons

We present a detailed study of the oscillations and optical properties for vacuum, in a model for the dark sector that contains axion-like particles and hidden photons. In this model, both can couple to photons. We provide bounds for the couplings versus the mass, using current results from ALPS-I and PVLAS. We also discuss the challenges for the detection of models with more than one hidden particle in light shining trough wall-like experiments.

hep-ph↗

arXiv2013

Information Measures of Complexity, Emergence, Self-organization, Homeostasis, and Autopoiesis

This chapter reviews measures of emergence, self-organization, complexity, homeostasis, and autopoiesis based on information theory. These measures are derived from proposed axioms and tested in two case studies: random Boolean networks and an Arctic lake ecosystem. Emergence is defined as the information a system or process produces. Self-organization is defined as the opposite of emergence, while complexity is defined as the balance between emergence and self-organization. Homeostasis reflects the stability of a system. Autopoiesis is defined as the ratio between the complexity of a system and the complexity of its environment. The proposed measures can be applied at different scales, which can be studied with multi-scale profiles.

nlin.AO↗