arXiv subjects

José Tarciso S. S. Junior

Publications and source records attributed to José Tarciso S. S. Junior.

At least 19 recordsLinked to original sources

arXiv2026

Accretion dynamics of thin and thick disks in charged Kalb-Ramond black holes

In this work, we investigate the accretion properties of an electrically charged, static, spherically symmetric black hole in Kalb-Ramond (KR) gravity, where a dimensionless parameter $l$ characterizes spontaneous Lorentz symmetry-breaking. We first constrain the free charge and KR parameter space, $(Q,l)$, by comparing the predicted shadow radius of this family of solutions with the bounds inferred from Event Horizon Telescope observations of Sagittarius A*. The inclusion of electric charge introduces a degeneracy between $Q$ and $l$, enlarging the region compatible with the observed shadow size and yielding the broad constraint $-0.3900 \leq l \leq 0.1898$, with part of the compatible parameter space extending into the naked-singularity sector. We then investigate relativistic accretion disks around the charged KR black hole within the above constraints. For geometrically thin disks, we compute the time averaged energy flux, temperature distribution, emission spectrum, time averaged torque, and mass-to-radiation conversion efficiency, finding that the radiative output increases for higher values of $l$, while lower values of $l$ suppress it. Furthermore, when coupled with the electric charge this effect is amplified. For geometrically thick, constant-angular momentum tori-shaped disks, Lorentz symmetry-breaking shifts the characteristic orbital radii, compresses the radial extent of equilibrium configurations, narrows the interval supporting finite equilibrium tori, and shifts the stationary-fluid topology toward open and unconfined configurations outside that interval. These results show how charge and spontaneous Lorentz symmetry-breaking jointly affect observational constraints and the structure and emission properties of black hole accretion flows, providing potential signatures of KR gravity in the strong-gravity regime.

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arXiv2026

Black bounce sourced by non-minimally coupled linear electrodynamics and a canonical scalar field through a thin shell at the throat

We construct a novel class of black bounce solutions within General Relativity, sourced by a canonical scalar field non-minimally coupled to linear electrodynamics, establishing a self-consistent framework in which regular black holes and traversable wormholes are supported by ordinary bulk matter, with the necessary exoticity confined to an infinitesimally thin defect at the bounce.

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arXiv2026

Regular Black Holes in General Relativity from Nonlinear Electrodynamics with de Sitter Cores

We present new regular black hole solutions in general relativity (GR) within a static, spherically symmetric framework governed by a variable equation of state, following the approach of [Class. Quant. Grav. 42, 025024 (2025)]. The matter supporting these geometries is identified as a purely magnetic monopole configuration of the Maxwell-Faraday tensor in the context of nonlinear electrodynamics (NLED). We explicitly reconstruct the corresponding NLED Lagrangian and analyze the asymptotic and central behaviors of the solutions. The geometric structure is examined through the metric functions, the regularity of the Kretschmann scalar, and the profiles of energy density and pressures, including a discussion of the resulting energy conditions. Using Event Horizon Telescope observations of Sgr A$^*$, we constrain the model parameters by comparing the predicted size of the central dark region with the inferred observational images, taking into account the effective geometry experienced by photons in the presence of NLED. Finally, we investigate the dynamical stability of these configurations under scalar perturbations by computing the quasinormal mode spectrum and performing a time-domain analysis.

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arXiv2026

Black bounce solutions in a realistic dark matter halo from M60*

We formulate a Simpson-Visser black bounce solution embedded in a dark matter halo. The latter is modeled using an empirical density profile calibrated from observations of the elliptical galaxy NGC 4649 (M60), based on imaging from the Hubble Space Telescope, stellar velocity dispersion data, and the dynamics of globular clusters. The resulting spacetime metric, in addition to retaining dependence on the mass parameter $m$, the asymptotic circular velocity $V_c$, and the halo scale radius $a$, also depends on the regularization parameter $q_H$. It reduces to the canonical black bounce solution without a halo in the limit $V_c\to0$ (or $a\to\infty$), and to the Schwarzschild solution with a dark matter halo when $q_H\to0$. We analyze the response of fundamental geometrical and physical quantities in the presence of a halo, such as the event horizon radius, the shadow size, and some curvature invariants. In particular, we show the observational range of the shadow radius, from the imaging of Sagittarius A*, constrains the parameter space of the solution to regular black hole configurations, excluding wormhole scenarios. We study the dynamics of massless particles here through the effective potential and examine thermodynamic properties, highlighting the impact on thermodynamic potentials in terms of entropy. Finally, we extend the analysis to scenarios with electromagnetic fields non-minimally coupled to a phantom scalar field, considering configurations with either purely magnetic or purely electric charge. Our results suggest that the dark matter halo influences both the internal geometry and the observational properties of black bounces, imposing constraints on the solution's parameter space from astrophysical data. This highlights the need to include astrophysical environments in modeling regular black holes and wormholes, offering new tests of gravity in the strong-field regime.

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arXiv2026

Scalar-Electromagnetic Couplings as Source of Deformed Black Hole: From Shadows to Thermodynamic Topology

We reconstruct a static and spherically symmetric black hole geometry originally proposed as an effective metric by identifying a consistent matter source derived from a fundamental action. The space-time is supported by a magnetically charged nonlinear electrodynamics (NED) field non-minimally coupled to a scalar field. Dimensional consistency reduces the parameter space to a single magnetic charge, and the inverse construction formalism yields a one-parameter family of electromagnetic Lagrangians $\mathcal{L}(F)=F^{n+1}/(n+1)$, encompassing both linear and nonlinear electrodynamics. We analyze the horizon structure and determine the critical magnetic charge separating black hole and horizonless configurations. The photon sphere and the corresponding shadow radius are computed, and observational bounds from the Event Horizon Telescope for Sagittarius A* constrain the allowed range of the magnetic charge. In the extended phase space thermodynamics, the solution satisfies the first law and the Smarr relation, exhibits a Hawking-Page phase transition, and presents a single change in stability without van der Waals-type critical behavior. We also investigate the topological properties of both the photon sphere and the thermodynamic parameter space. The photon sphere carries a total topological charge $Q_{\text{tot}}=-1$, while the thermodynamic vector field yields a global winding number $W=0$, placing the solution in the same topological class as the one of the Reissner-Nordström black hole. We finally discuss the versatility of this non-minimal coupling framework in both providing theoretical support to previously introduced solution and also to connect them to observational settings within strong-field gravity.

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arXiv2025

Free-falling test particles in a charged Kalb-Ramond black hole: gravitational Doppler effect and tidal forces

Space-times exhibiting spontaneous Lorentz symmetry-breaking have recently attracted much attention, with Kalb-Ramond (KR) gravity providing a notable example. In this context, we examine the free-fall motion of a test particle toward an electrically charged black hole arising from the coupling of the KR field with the Maxwell one in General Relativity. We investigate how the Lorentz symmetry-breaking parameter affects the free-fall velocity of the particle as it approaches black hole inner regions. Additionally, we analyze the influence of this parameter on the emission and detection of signals by observers in different frames. We furthermore explore modifications to the radial and angular components of tidal forces in this space-time and compare the results with those obtained for the Reissner-Nordström black hole. Finally, we analytically solve the geodesic deviation equation under two different conditions, identifying a subtle effect of the Lorentz symmetry breaking parameter in the charged KR metric, and compare it with two other space-time metrics with spontaneous symmetry breaking. These findings provide useful insights into how models of spontaneous Lorentz symmetry-breaking influence gravitational dynamics in the space-times of charged black holes.

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arXiv2025

Regular Bardeen black holes within non-minimal scalar-linear electrodynamic couplings

In this paper, we demonstrate that a linear electromagnetic matter source can be constructed for regular black hole solutions, illustrated by the case of the Bardeen black hole. Our method relies on coupling a scalar field and its potential to General Relativity (GR) alongside electrodynamics. Both fields are minimally coupled to GR but interact with each other. We validate this approach by interpreting the Bardeen solution either as a purely magnetic or as a purely electric configuration for a spherically symmetric metric with an arbitrary electrodynamics Lagrangian $\mathcal{L}(F)$ and a coupling function $W(φ)$. By choosing an appropriate form of $W$, the electromagnetic Lagrangian can be rendered linear. We then analyze the behavior of the coupling function and the scalar field potential, emphasizing their relation to the magnetic or electric charge. Finally, we compare the advantages and disadvantages of this framework with the conventional formalism, in which regular charged black holes are supported solely by nonlinear electrodynamics.

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arXiv2025

Black bounce solutions via nonminimal scalar-electrodynamic couplings

Black-bounce (BB) solutions generalize the spacetimes of black holes, regular black holes, and wormholes, depending on the values of certain characteristic parameters. In this work, we investigate such solutions within the framework of General Relativity (GR), assuming spherical symmetry and static geometry. It is well established in the literature that, in order to sustain such geometries, the source of Einstein's equations in the BB context can be composed of a scalar field $φ$ and a nonlinear electrodynamics (NLED). In our model, in addition to the Lagrangian associated with the scalar field in the action, we also include an interaction term of the form $W(φ)\mathcal{L}(F)$, which introduces a nonminimal coupling between the scalar field and the electromagnetic sector. Notably, the usual minimal coupling configuration is recovered by setting $W(φ)=1$. In contrast to approaches where the function $W(φ)$ is assumed a priori, here we determine its functional form by modeling the radial dependence of the derivative of the electromagnetic Lagrangian as a power law, namely $\mathcal{L}_F(r) \sim F^n$. This approach enables us to determine $W(r)$ directly from the obtained solutions. We apply this procedure to two specific geometries: the Simpson-Visser-type BB solution and the Bardeen-type BB solution, both analyzed in the purely magnetic ($q_m \neq 0$, $q_e=0$) and purely electric ($q_m=0$, $q_e \neq 0$) cases. In all scenarios, we find that these BB spacetime solutions can be described with a linear electrodynamics, which is a noteworthy result. Furthermore, we examine the regularity of the spacetime through the Kretschmann scalar and briefly discuss the associated energy conditions for the solutions obtained.

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arXiv2025

Accretion dynamics in black holes with spontaneous Lorentz symmetry breaking

We investigate the spherical accretion of various types of fluids onto a Schwarzschild-like black hole solution modified by a Kalb-Ramond field implementing spontaneous Lorentz symmetry violation (LV). The system is analyzed for isothermal fluids characterized by the equation of state $p=ωρ$, including ultra-stiff, ultra-relativistic, and radiation fluids. We investigate the effect of the LV parameter $l$ on the fluid density $ρ(r)$, radial velocity $u(r)$, and accretion rate $\dot{M}$. Using a Hamiltonian dynamical systems approach, we examine the behavior near critical points and identify the sonic transitions in each scenario. Our results show that the LV parameter influences the location of critical points, the flow structure, and the accretion rate, with $l>0$ ($l<0$) enhancing (suppressing) the latter. For ultra-stiff fluids, no critical points are found, and the flow remains entirely subsonic. For ultra-relativistic and radiation fluids, transonic solutions exist, with the position of the sonic point depending on the sign of $l$. We also analyze polytropic fluids $p=\mathcal{K} ρ^Γ$ with $Γ=5/3$ and $Γ=4/3$, observing similar qualitative behavior, where the sonic transition is affected by both the equation of state and the LV parameter. These findings suggest that Lorentz symmetry breaking can significantly alter accretion dynamics in black hole spacetimes.

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arXiv2025

Black hole solutions in Cotton gravity coupled to nonlinear electrodynamics

The framework of General Relativity (GR) has recently been expanded through the introduction of Cotton Gravity (CG), a theoretical extension proposed by J. Harada. This modified approach integrates the Cotton tensor into the gravitational field equations, naturally encompassing all conventional GR solutions while allowing the cosmological constant to emerge as an integration constant. In this study, we delve into the implications of CG when coupled with nonlinear electrodynamics (NLED), constructing and analyzing three distinct static, spherically symmetric configurations. Our investigation centers on the horizon structure, metric characteristics, and the underlying NLED Lagrangian density of each model. We also confront the theoretical predictions with observational data by comparing the calculated shadow radii of these solutions to constraints imposed by the Event Horizon Telescope's (EHT) measurements of Sgr A$^{*}$. The results reveal an extensive spectrum of spacetime geometries, ranging from multi-horizon structures to naked singularities. Furthermore, the agreement between the predicted shadow sizes and EHT observations reinforces the viability of these models in describing the astrophysical image of Sgr A$^{*}$ within certain parameter bounds.

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arXiv2025

Constraints on the $γ$-parameter for the vacuum solution of Cotton gravity with geodesics and shadows

We consider a recently introduced extension of General Relativity dubbed as Cotton gravity (CG), based on the use of the Cotton tensor, to estimate the size of a new constant $γ$ appearing within a spherically symmetric, vacuum solution of the theory. Taking into account its non-asymptotically flat character, we use the inferred size of the central brightness depression of the supermassive object at the heart of the Milky Way galaxy (Sgr A*) by the Event Horizon Telescope to constrain at $2σ$ the CG parameter as $γM \approx 3.5 \times 10^{-12}$. We study the potential observational consequences from the smallness of such a value using exact and numerical expressions for the deflection angle, optical images from optically and geometrically thin accretion disks, isoradials, and instability scales (Lyapunov index) of nearly bound geodesics associated to photon rings. Our results point towards the impossibility to distinguish between these two geometries using current and foreseeable techniques in the field of interferometric detection of optical sources.

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arXiv2025

Horizons, throats and bounces in hybrid metric-Palatini gravity with a non-zero potential

This work conducts an in-depth exploration of exact electrically charged solutions, including traversable wormholes, black holes, and black bounces, within the framework of the scalar-tensor representation of hybrid metric-Palatini gravity (HMPG) with a non-zero scalar potential. By integrating principles from both the metric and Palatini formulations, HMPG provides a flexible approach to addressing persistent challenges in General Relativity (GR), such as the late-time cosmic acceleration and the nature of dark matter. Under the assumption of spherical symmetry, we employ an inverse problem technique to derive exact solutions in both the Jordan and Einstein conformal frames. This method naturally leads to configurations involving either canonical or phantom scalar fields. A thorough examination of horizon structures, throat conditions, asymptotic behaviour, and curvature regularity (via the Kretschmann scalar) reveals the intricate causal structures permitted by this theoretical model. The analysis uncovers a diverse range of geometric configurations, with the phantom sector exhibiting a notably richer spectrum of solutions than the canonical case. These solutions encompass traversable wormholes, black universe models, where the interior of a black hole evolves into an expanding cosmological phase rather than a singularity, as well as black bounce structures and multi-horizon black holes. The results demonstrate that introducing a non-zero scalar potential within HMPG significantly expands the array of possible gravitational solutions, yielding complex causal and curvature properties that go beyond standard GR. Consequently, HMPG stands out as a powerful theoretical framework for modelling extreme astrophysical environments, where deviations from classical gravity are expected to play a crucial role.

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arXiv2025

Dyonic regular black bounce solutions in General Relativity

This work explores dyonic black bounce (BB) solutions within the framework of General Relativity (GR), coupled with nonlinear electrodynamics (NLED) and scalar fields (SFs). Previous research has employed NLED and SFs to obtain BB solutions in GR; however, these solutions typically assume the presence of either magnetic monopoles or electric charges exclusively as components of the Maxwell-Faraday tensor. In this study, we examine static and spherically symmetric BB solutions that incorporate both magnetic and electric components, forming what are known as dyon solutions. A dyon is a particle characterized by the coexistence of both magnetic and electric charges. We determine the NLED Lagrangian density and the scalar field potential that produce these solutions and analyze the associated gravitational configurations, focusing on horizons, the behavior of the metric function, and spacetime regularity as described by the Kretschmann scalar. Notably, we present the first BB solution derived from the coupling of a linear electromagnetic Lagrangian and a scalar field with an associated potential as the matter source. This work broadens the class of non-singular geometries in the literature and opens new avenues for investigating dyonic BB solutions within the context of other modified gravity theories.

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arXiv2025

Charged black hole solutions in $f(R,T)$ gravity coupled to nonlinear electrodynamics

In this work, we investigate static and spherically symmetric black hole solutions in $f(R,T)$ gravity, where $R$ is the curvature scalar and $T$ is the trace of the energy-momentum tensor, coupled to nonlinear electrodynamics (NLED). To construct our solutions, we adopt a linear functional form, $f(R,T) = R + βT$. In the limit $β= 0$, the theory reduces to General Relativity (GR), recovering $f(R,T) \approx R$. We propose a power-law Lagrangian of the form $\mathcal{L} = f_0 + F + αF^p$, where $α=f_0= 0$ corresponds to the linear electrodynamics case. Using this setup, we derive the metric functions and determine an effective cosmological constant. Our analysis focuses on specific cases with $p = 2$, $p = 4$, and $p = 6$, where we formulate analytic expressions for the matter fields supporting these solutions in terms of the Lagrangian as a function of $F$. Additionally, we verify the regularity of the solutions and study the structure of the event horizons. Furthermore, we examine a more specific scenario by determining the free forms of the first and second derivatives $\mathcal{L}_F(r)$ and $\mathcal{L}_{FF}(r)$ of the Lagrangean of the nonlinear electromagnetic field. From these relations, we derive the general form of $\mathcal{L}_{\text{NLED}}(r)$ using consistency relations. This Lagrangian exhibits an intrinsic nonlinearity due to the influence of two constants, $α$ and $β$. Specifically, $α$ originates from the power-law term in the proposed Lagrangian, while $β$ arises from the assumed linear function $f(R,T)$. The interplay of these constants ensures that the nonlinearity of the Lagrangian is governed by both $α$ and $β$, rather than $α$ alone.

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arXiv2025

Periodical orbits and waveforms with spontaneous Lorentz symmetry-breaking in Kalb-Ramond gravity

In this paper, we study time-like geodesics around a spherically symmetric black hole in Kalb-Ramond (KR) gravity, characterized by the parameter $l$, which induces spontaneous Lorentz symmetry breaking. The geodesic equations and effective potential are derived to investigate the influence of $l$. We calculate the marginally bound orbits and innermost stable circular orbits, analyzing the parameter's impact. Periodic orbits are computed numerically and classified within the standard taxonomy, revealing significant effects of $l$ on their momentum and energy. Additionally, we explore an extreme mass ratio inspiral system under the adiabatic approximation to derive gravitational waveforms emitted by an object orbiting a supermassive black hole in KR gravity. These waveforms reflect the distinctive characteristics of periodic orbits and highlight the influence of $l$. With advancements in gravitational wave detection, these results offer insights into black holes influenced by Lorentz symmetry-breaking fields.

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arXiv2025

Novel electrically charged wormhole, black hole and black bounce exact solutions in hybrid metric-Palatini gravity

This paper presents a systematic exploration of exact solutions for electrically charged wormholes, black holes, and black bounces within the hybrid metric-Palatini gravity (HMPG) framework. HMPG combines features of the metric and Palatini formulations of modified gravity, offering a powerful approach to address challenges in General Relativity, particularly those related to cosmic acceleration and dark matter. We examine configurations characterized by a zero scalar potential under spherical symmetry, and present solutions in both the Jordan and Einstein conformal frames. A diverse set of solutions emerges, including traversable wormholes, black holes with double horizons, and ``black universe'' models in which spacetime beyond the horizon leads to an expanding cosmological solution rather than a singularity. Each configuration is categorized according to the properties of the scalar field, with an in-depth analysis of the horizon and throat structures, asymptotic behaviour, and singularities. These findings underscore the versatility of HMPG in capturing complex gravitational phenomena and broadens the scope of the theory, offering a robust framework for modelling gravitational phenomena across a range of astrophysical contexts. Future work will benefit from extending these solutions to include scalar potentials, addressing both early-universe inflation and late-time acceleration, and applying observational data, such as gravitational lensing and gravitational wave measurements.

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arXiv2025

Novel charged black hole solutions in conformal Killing gravity

In this paper, we investigate static spherically symmetric solutions in the context of Conformal Killing Gravity, a recently proposed modified theory of gravity that offers a new approach to the cosmological constant problem. Coupling this new theory with nonlinear electrodynamics, we derive the corresponding field equations and study their behavior under different parameter choices. We analyze three different models, each focusing on different key parameters. Our results reveal a rich causal structure with multiple horizons and transitions between extreme and non-extreme solutions depending on the parameter values. Moreover, we compute the nonlinear Lagrangian density for each model and find that it agrees with Maxwell theory in the limit $F \rightarrow 0$. We also confirm the existence of a central curvature singularity via the Kretschmann scalar. To connect our theoretical results with observational prospects, we study the black hole shadows associated with each model. The analysis shows that the calculated shadow size and shape of the three proposed models are consistent with the data for the supermassive object at the center of our galaxy and are therefore possible candidates for modeling this structure.

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arXiv2024

Spontaneous Lorentz symmetry-breaking constraints in Kalb-Ramond gravity

In this work, we study timelike and lightlike geodesics in Kalb-Ramond (KR) gravity around a black hole with the goal of constraining the Lorentz symmetry-breaking parameter $l$. The analysis involves studying the precession of the S2 star periastron orbiting Sgr A* and geodesic precession around the Earth. The ratio of precession frequencies for General Relativity (GR) and KR gravity is computed, with Event Horizon Telescope (EHT) results providing a parameter range for the spontaneous symmetry-breaking of $-0.185022 \leq l \leq 0.060938$. Utilizing the geodesic precession frequency from the Gravity Probe B (GP-B), the $l$ parameter is further constrained to $-6.30714 \times 10^{-12} \leq l \leq 3.90708 \times 10^{-12}$, which is consistent with the Schwarzschild limits. Moreover, for timelike geodesics, the innermost circular orbit (ICO) and innermost stable circular orbit (ISCO) are determined and analyzed to illustrate the impact of the symmetry breaking term. Zoom-whirl obstructions are compared with the Schwarzschild solution. Lower and upper limits of the photon sphere for lightlike geodesics are established to demonstrate the influence of KR gravity on the photon sphere. Additionally, the shadow radius is determined for two observers, one situated at a finite distance from the KR black hole, and the other located at an infinite distance, to constrain the symmetry-breaking parameter $l$, with comparisons made to EHT results. The bounds for $l$ derived from constraints on the photon sphere radius for lightlike geodesics yield $-0.0700225 \leq l \leq 0.189785$ using EHT data. The findings of this paper align with experimental results in the $l \rightarrow 0$ limit.

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