arXiv subjects

Mauricio Cataldo

Publications and source records attributed to Mauricio Cataldo.

At least 19 recordsLinked to original sources

arXiv2026

Static electric and magnetic traversable wormholes in $(2+1)$-dimensional nonlinear electrodynamics

Every traversable wormhole reported so far in static (2+1) gravity coupled to nonlinear electrodynamics has come from a power-Maxwell Lagrangian L propto |F|^k restricted to k=1/2, always forcing the cosmological constant to a fixed sign or zero. We show these restrictions are artefacts of that single choice, not physical requirements, and give a complete classification of static traversable wormholes in this theory. Of the three mutually exclusive electromagnetic configurations compatible with the symmetry, the radial electric branch admits no throat for any Lagrangian or Lambda. In each remaining branch, azimuthal electric and magnetic, the field equations admit exactly two regimes: either the redshift function is fixed, leaving the shape function b(r) completely free with Lambda absorbed without constraint; or the redshift is generic, in which case b(r) becomes fixed instead. We solve both regimes in closed form in both branches, and show that fixing the Lagrangian to any single power k forces Lambda nonzero and determines b(r) up to finitely many constants: this freedom requires the Lagrangian to be genuinely unrestricted. One azimuthal-electric family reproduces the static BTZ mass function, turning the vacuum black hole into a wormhole once sourced by the nonlinear field. Applied to the unique conformal power-Maxwell theory, k=3/4, previously known only as a radial-branch charged black hole, the same Lagrangian yields genuine wormholes in the azimuthal and magnetic branches, showing the electromagnetic configuration, not the Lagrangian, decides between a horizon and a throat; Born-Infeld electrodynamics admits no throat in any branch.

gr-qc↗

arXiv2026

Non-exotic traversable wormholes in Einstein-Chern-Simons gravity

We investigate traversable wormhole solutions in five-dimensional Einstein-Chern-Simons (EChS) gravity, a gauge-theoretic extension of General Relativity that introduces a higher-curvature correction parametrized by the combination $\alpha l^2$, where $\alpha$ is a dimensionless coupling and $l$ is a length scale. Working with the Morris-Thorne metric and an anisotropic fluid, we derive exact expressions for the energy density, radial pressure, and lateral pressure at the wormhole throat. We show that the radial Null Energy Condition (NEC) is satisfied at the throat if and only if $\alpha l^2\leq-r_0^2$, being saturated at $\alpha l^2=-r_0^2$ and strictly satisfied for $\alpha l^2<-r_0^2$, independently of the shape function. In the latter regime, the energy density is strictly positive and the full NEC, Weak, Strong, and Dominant Energy Conditions can be simultaneously satisfied. These results are established analytically for arbitrary shape functions and illustrated concretely for the power-law family $b(r)=r_0(r_0/r)^n$, $\Phi=0$, for which all four standard energy conditions are satisfied at the throat for all $n>0$ when the EChS coupling is sufficiently negative. We further show that the radial pressure is negative and geometrically fixed at the throat, independently of $\alpha$, $b(r)$, and $\Phi(r)$. Using the Volume Integral Quantifier (VIQ), we establish that the EChS correction reduces the magnitude of the negative integrated NEC contribution relative to GR, and derive an exact closed-form critical coupling $\alpha l^2_{\rm crit}$ at which the VIQ vanishes. The hierarchy $\alpha l^2_{\rm crit}<-r_0^2<0$ shows that NEC satisfaction at the throat and a non-negative global VIQ are compatible but distinct conditions, both achievable within EChS gravity. All results reduce continuously to those of GR in the limit $l\to0$, confirming the consistency of the framework.

gr-qc↗

arXiv2026

On the geometrical and dynamical distinction between Unimodular and General Relativistic wormholes

We characterize traversable wormholes in Unimodular Gravity (UG) and investigate what distinguishes them from their General Relativistic (GR) counterparts. For a class of static and spherically symmetric solutions, we analyze their embedding and timelike geodesics, showing that the geodesic structure is entirely determined by the metric and is therefore identical in both theories. To identify the physical origin of their differences, we compare the source sectors required to sustain the same wormhole geometry. We find that preserving a fixed UG geometry while imposing energy-momentum conservation requires restricting the equation of state, whereas relaxing this condition introduces an effective inhomogeneous vacuum contribution. We further show that the degree of exoticity is preserved even when energy-momentum is not conserved, while departures from the GR sector are encoded in an effective inhomogeneous vacuum structure whose asymptotic behavior resembles that of a cosmological constant. Our results reinforce that UG is geometrically equivalent to GR, while its distinctive features emerge in the dynamical interpretation of the source sector. More generally, our analysis illustrates that different gravitational theories may give rise to identical spacetime geometries while requiring different sources to sustain them.

gr-qc↗

arXiv2026

Comment on Cosmological constraints on unimodular gravity models with diffusion (arXiv:2211.07424): thermodynamic inadmissibility of the H0 tension resolution mechanism

We show that the diffusion-based models proposed in Refs.~\cite{Perez2021,Landau2022} within the framework of Unimodular Gravity (UG) to alleviate the $H_0$ tension are incompatible with the second law of thermodynamics. Starting from the Gibbs equation for a pressureless matter fluid, we derive a general thermodynamic admissibility condition for the $Λ$CDM$+$diffusion class in UG, demonstrating that the second law requires $\dot{Q} < 0$, independently of the specific form of the diffusion function $Q(t)$. This condition implies that energy must flow from the effective cosmological term $Λ_{\rm eff}$ into the matter sector, rather than in the opposite direction. We then establish a no-go theorem: no choice of $Q(t)$ can simultaneously satisfy the second law and generate the growing effective cosmological term $\dotΛ_{\rm eff} > 0$ required to alleviate the $H_0$ tension. We confirm this result explicitly for the models of Perez, Sudarsky, and Wilson-Ewing~\cite{Perez2021} and Landau et al.~\cite{Landau2022}, noting that the former explicitly identify $\dotΛ_{\rm eff} > 0$ as a necessary feature of their proposal without addressing its thermodynamic implications. The incompatibility is therefore structural and applies to the entire class of $Λ$CDM$+$diffusion models in UG with a pressureless matter component.

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arXiv2026

Can wormhole spacetimes in Unimodular Gravity be supported by ordinary matter? A general proof of the exotic matter requirement

We establish a general no--go theorem demonstrating that all traversable wormhole configurations in Unimodular Gravity necessarily require exotic matter. The proof relies solely on the geometric flaring-out condition, $b'(r_0) \leq 1$, which directly implies that $ρ(r_0) + p_r(r_0) \leq 0$ at the throat. This condition represents a violation of the Null Energy Condition and, consequently, of the Weak and Strong Energy Conditions, independently of the particular choice of shape function, redshift function, or equation of state. This result holds for both tidal and zero-tidal-force configurations, showing that the requirement of exotic matter is a fundamental geometric consequence of the traversability condition rather than an artifact of specific solution choices. Therefore, Unimodular Gravity shares this fundamental constraint with General Relativity.

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arXiv2025

Could a thin-shell configuration lie hidden within the Universe?

This article explores the cosmological scenario in which our Universe contains a hidden thin-shell configuration. We investigate a degenerate modification of the Friedmann-Robertson-Walker metric obtained through a coordinate transformation applied to the radial coordinate, analogous to recent approaches that address the Big Bang singularity via spacetime defects. The resulting metric, while formally satisfying the standard homogeneous Friedmann equations, actually describes an evolving wormhole geometry with two asymptotically flat Friedmann-Robertson-Walker regions connected by a throat located at the coordinate singularity. Using Israel's junction formalism, we demonstrate that this coordinate singularity corresponds to a thin shell characterized by exotic matter with well-defined surface energy density and isotropic pressure. The shell obeys the barotropic equation of state $p = -ρ/2$, confirming the presence of exotic matter that violates the standard energy condition, which is a requirement for maintaining wormhole geometries. As the universe expands, this thin shell becomes increasingly diluted, scaling as $1/a(t)$ with the cosmic scale factor.

gr-qc↗

arXiv2025

On non-equatorial embeddings into $\mathbb{R}^3$ of spherically symmetric wormholes with topological defects

Traditionally, the embedding procedure for spherically symmetric spacetimes has been restricted to the equatorial plane $θ= π/2$. This conventional approach, however, encounters a fundamental limitation: not every spherically symmetric geometry admits an isometric embedding of its equatorial slice into three-dimensional Euclidean space. When such embeddings are not possible, the standard geometric intuition becomes inapplicable. In this work, we generalize the embedding procedure to slices with arbitrary polar angles $θ\neq π/2$, thereby extending the visualization and analysis of spacetimes beyond the reach of traditional methods. The formalism is applied to Schwarzschild-like wormholes and to a generalized Minkowski spacetime with angular deficit or excess, which are particularly relevant since their equatorial slices cannot be consistently embedded in $\mathbb{R}^3$. In these cases, we identify the explicit constraints on the radial coordinate, polar angle, and geometric parameters required to guarantee consistent embeddings into three-dimensional Euclidean space.

gr-qc↗

arXiv2025

Revisiting Wormhole Solutions in Unimodular Gravity: Energy Conditions and Exotic Matter Requirements

The paper entitled Unimodular Gravity Traversable Wormholes by Agrawal et al. examined the properties of barotropic wormholes without tidal forces within the framework of Unimodular Gravity. Our analysis demonstrates that their conclusion regarding the possibility of sustaining such wormhole configurations with ordinary matter is not entirely accurate. We establish that exotic matter remains necessary for these wormhole solutions in Unimodular Gravity, in accordance with the long-established theoretical constraints already identified in General Relativity.

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arXiv2021

Thermodynamics of 2+1 dimensional Coulomb-Like Black Holes from Non Linear Electrodynamics with a traceless energy momentum tensor

In this work we study thermodynamics of 2+1-dimensional static black holes with a nonlinear electric field. Besides employing the standard thermodynamic approach, we investigate the black hole thermodynamics by studying its thermodynamic geometry. We compute the Weinhold and Ruppeiner metrics and compare the thermodynamic geometry with the standard description on the black hole thermodynamics. We further consider the cosmological constant as an additional extensive thermodynamic variable. In the thermodynamic equilibrium three dimensional space, we compute the efficiency of the heat engine and show that it is possible to be built with this black hole.

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arXiv2020

Bayesian Comparison of Interacting Modified Holographic Ricci Dark Energy Scenarios

We perform a Bayesian model selection analysis for interacting scenarios of dark matter and modified holographic Ricci dark energy (MHRDE) with linear interacting terms. We use a combination of some of the latest cosmological data such as type Ia supernovae, cosmic chronometers, cosmic microwave background and baryon acoustic oscillations measurements. We find strong evidence against all the MHRDE interacting scenarios studied with respect to $Λ$CDM when the full joint analysis is considered.

astro-ph.CO↗

arXiv2019

Modelling the current accelerated expansion of the Universe with Holographic Dark Energy

In this work we explore a Holographic Dark Energy Model in a flat Friedmann-Lemaître-Robertson-Walker Universe, which contains baryons, radiation, cold dark matter and dark energy within the framework of General Relativity. Furthermore, we consider three types of phenomenological interactions in the dark sector. With the proposed model we obtained the algebraic expressions for the cosmological parameters of our interest: the deceleration and coincidence parameters. Likewise, we graphically compare the proposed model with the $Λ$CDM model.

gr-qc↗

arXiv2018

The Hubble IR cutoff in holographic ellipsoidal cosmologies

It is well known that for spatially flat FRW cosmologies, the holographic dark energy disfavours the Hubble parameter as a candidate for the IR cutoff. For overcoming this problem, we explore the use of this cutoff in holographic ellipsoidal cosmological models, and derive the general ellipsoidal metric induced by a such holographic energy density. Despite the drawbacks that this cutoff presents in homogeneous and isotropic universes, based on this general metric, we developed a suitable ellipsoidal holographic cosmological model, filled with a dark matter and a dark energy components. At late time stages, the cosmic evolution is dominated by a holographic anisotropic dark energy with barotropic equations of state. The cosmologies expand in all directions in accelerated manner. Since the ellipsoidal cosmologies given here are not asymptotically FRW, the deviation from homogeneity and isotropy of the universe on large cosmological scales remains constant during all cosmic evolution. This feature allows studied holographic ellipsoidal cosmologies to be ruled by an equation of state $ω=p/ρ$, whose range belongs to quintessence or even phantom matter.

gr-qc↗

arXiv2017

Static phantom wormholes of finite size

In this paper we derive new static phantom traversable wormholes by assuming a shape function with a quadratic dependence on the radial coordinate r. We mainly focus our study on wormholes sustained by exotic matter with positive energy density (as seen by any static observer) and a variable equation of state $p_r/ρ<-1$, dubbed phantom matter. Among phantom wormhole spacetimes extending to infinity, we show that a quadratic shape function allows us to construct static spacetimes of finite size, composed by a phantom wormhole connected to an anisotropic spherically symmetric distribution of dark energy. The wormhole part of the full spacetime does not fulfill the dominant energy condition, while the dark energy part does.

gr-qc↗

arXiv2017

Finite time future singularities in the interacting dark sector

We construct a piecewise model that gives a physical viable realization of finite-time future singularity for a spatially flat Friedmann-Robertson-Walker universe within the interacting dark matter--dark energy framework, with the latter one in the form of a variable vacuum energy. The scale factor solutions provided by the model are accommodated in several branches defined in four regions delimited by the scale factor and the effective energy density. A branch starts from a big bang singularity and describes an expanding matter-dominated universe until the sudden future singularity occurs. Then, an expanding branch emerges from a past singularity, reaches a maximum, reverses its expansion and possibly collapses into itself while another expanding branch emerges from the latter singularity and has a stable de Sitter phase which is intrinsically stable. We obtain a different piecewise scale factor which describes a contracting de Sitter universe in the distant past until the finite-time future singularity happens. It emerges and continues in a contracting phase, bounces at the minimum, reverses, and enters into a stable de Sitter phase without a dramatic final. Also, we explore the aforesaid cosmic scenarios by focusing on the leading contributions of some physical quantities near the sudden future singularity and applying the geometric Tipler and Królak criteria in order to inspect the behavior of timelike geodesic curves around such singularity.

gr-qc↗

arXiv2016

Cosmic anisotropic doomsday in Bianchi type I universes

In order to investigate if the anisotropy of the spacetime may induce future singularities at a finite value of the cosmic time on the evolution of cosmological models, we study vacuum and non-vacuum Bianchi type I spacetimes exhibiting such future singularities. We show that in the case of Kasner vacuum cosmologies the spacetime may rip itself apart in a finite time, and only in the direction corresponding to the unique scale factor which diverges at this finite value of the cosmic time. The other two directional scale factors and the average scale factor do not diverge and tend to zero at this time, while the directional and average expansion rates also become infinite. Due to the absence of the matter content this anisotropic future singularity is induced by the shear scalar, which also blows up at this time. We call such a singularity "Vacuum Rip". For non-vacuum solutions we discuss fully anisotropic Bianchi type I spacetimes filled with a stiff fluid and ellipsoidal (axisymmetric) cosmological models filled with matter with isotropic and anisotropic barotropic pressure, and characterized by $σ/θ=const$, where $σ$ and $θ$ are the shear scalar and the expansion scalar respectively.

gr-qc↗

arXiv2016

Static spherically symmetric wormholes with isotropic pressure

In this paper we study static spherically symmetric wormhole solutions sustained by matter sources with isotropic pressure. We show that such spherical wormholes do not exist in the framework of zero-tidal-force wormholes. On the other hand, it is shown that for the often used power-law shape function there is no spherically symmetric traversable wormholes sustained by sources with a linear equation of state $p=ωρ$ for the isotropic pressure, independently of the form of the redshift function $ϕ(r)$. We consider a solution obtained by Tolman at 1939 for describing static spheres of isotropic fluids, and show that it also may describe wormhole spacetimes with a power-law redshift function, which leads to a polynomial shape function, generalizing a power-law shape function, and inducing a solid angle deficit.

gr-qc↗

arXiv2015

Morris-Thorne wormholes in static pseudo-spherically symmetric spacetimes

In this paper we study classical general relativistic static wormhole configurations with pseudo-spherical symmetry. We show that in addition to the hyperbolic wormhole solutions discussed by Lobo and Mimoso in the Ref. Phys.\ Rev.\ D {\bf 82}, 044034 (2010), there exists another wormhole class, which is truly pseudo-spherical counterpart of spherical Morris-Thorne wormhole (contrary to the Lobo-Mimoso wormhole class), since all constraints originally defined by Morris and Thorne for spherically symmetric wormholes are satisfied. We show that, for both classes of hyperbolic wormholes the energy density, at the throat, is always negative, while the radial pressure is positive, contrary to the spherically symmetric Morris-Thorne wormhole. Specific hyperbolic wormholes are constructed and discussed by imposing different conditions for the radial and lateral pressures, or by considering restricted choices for the redshift and the shape functions. In particular, we show that an hyperbolic wormhole can not be sustained at the throat by phantom energy, and that there are pseudo-spherically symmetric wormholes supported by matter with isotropic pressure and characterized by space sections with an angle deficit (or excess).

gr-qc↗

arXiv2014

Accelerated FRW Solutions in Chern-Simons Gravity

We consider a five-dimensional Einstein-Chern-Simons action which is composed of a gravitational sector and a sector of matter, where the gravitational sector is given by a Chern-Simons gravity action instead of the Einstein-Hilbert action and where the matter sector is given by the so called perfect fluid. It is shown that (i) the Einstein-Chern-Simons (EChS) field equations subject to suitable conditions can be written in a similar way to the Einstein-Maxwell field equations; (ii) these equations have solutions that describe accelerated expansion for the three possible cosmological models of the universe, namely, spherical expansion, flat expansion and hyperbolic expansion when $α$, a parameter of theory, is greater than zero. This result allow us to conjeture that this solutions are compatible with the era of Dark Energy and that the energy-momentum tensor for the field $h^{a}$, a bosonic gauge field from the Chern-Simons gravity action, corresponds to a form of positive cosmological constant. It is also shown that the EChS field equations have solutions compatible with the era of matter: (i) In the case of an open universe, the solutions correspond to an accelerated expansion ($α>0$) with a minimum scale factor at initial time that, when the time goes to infinity, the scale factor behaves as a hyperbolic sine function. (ii) In the case of a flat universe, the solutions describing an accelerated expansion whose scale factor behaves as a exponencial function when time grows. \item In the case of a closed universe it is found only one solution for a universe in expansion, which behaves as a hyperbolic cosine function when time grows.

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