arXiv subjects

R. V. Maluf

Publications and source records attributed to R. V. Maluf.

At least 19 recordsLinked to original sources

arXiv2025

Fermionic greybody factors and strong gravitational lensing by Lorentz-violating global monopole

In this work, we study the greybody factors (GFs) of spin 1/2 and spin 3/2 fermions for a black hole with global monopole in self-interacting Kalb-Ramond gravity with Lorentz symmetry violation. For our purpose, we consider the Dirac and Rarita-Schwinger equations in curved spacetime by proceeding with separating these equations into sets of radial and angular equations. Using the analytical solution of the angular equation, the Schrödinger-like wave equations with potentials are derived by decoupling the radial wave equations using the tortoise coordinate. Moreover, we calculate the angular deflection of light in the strong field limit. With the expression for angular deflection in the strong field limit, we compute the positions as well as magnification of the respective relativistic images. We compute the shadows cast by the Lorentz-violating (LV) black hole with a global monopole and analyze how the LV parameter and the monopole charge affect the shadows.

gr-qc↗

arXiv2025

Global monopole in a Ricci-coupled Kalb-Ramond bumblebee gravity

In this paper, we investigate black hole solutions in Einstein-Kalb-Ramond (EKR) bumblebee gravity sourced by a global monopole characterized by the charge $η$. This modified theory of gravity possesses the notable feature of incorporating local Lorentz symmetry breaking (LSB) via a spontaneous symmetry-breaking mechanism. We solve the field equations for a static and spherically symmetric metric with the Kalb-Ramond (KR) field fixed at its VEV, thereby obtaining new black hole solutions. These solutions simultaneously exhibit the LSB effects, codified by the $γ$ parameter, and the global monopole effects, codified by the charge $η$. Next, we study the impact of the global monopole and LSB corrections on two classical tests, namely, the advance of Mercury's perihelion and the light deflection. Furthermore, we compute the Hawking temperature, black hole shadows, and greybody factors. Ultimately, we estimate an upper bound for $η$ by comparing the theoretical results provided by the EKR model with observational data from the advance of Mercury's perihelion and light deflection.

gr-qc↗

arXiv2025

Perturbative solutions for compact objects in (2+1)-dimensional Bopp-Podolsky electrodynamics

We investigate the space-time geometry generated by compact objects in (2+1)-dimensional Bopp-Podolsky electrodynamics. Inspired by previous studies where the Bopp-Podolsky field acts as a source for spherically symmetric solutions, we revisit this question within the lower-dimensional (2+1) framework. Using a perturbative approach, we derive a charged BTZ-like black hole solution and compute corrections up to second order in a perturbative expansion valid far from the horizon. Our analysis suggests that the near-horizon and inner structure of the solution remain unaltered, indicating that no new non-black hole objects emerge in this regime. In particular, we do not find evidence of wormhole solutions in the (2+1)-dimensional version of this theory.

gr-qc↗

arXiv2024

Generating 4-dimensional Wormholes with Yang-Mills Casimir Sources

This work presents a new wormhole solution in General Relativity supported by the quantum vacuum fluctuations of the Casimir effect between perfect chromometallic mirrors in $(3+1)$ dimensions, which was recently fitted using first-principle numerical simulations. Initially, we employ a perturbative approach for $x = m r \ll 1$, where $m$ represents the Casimir mass. This approach has proven to be a reasonable approximation when compared with the exact case in this regime. To find well-behaved redshift functions, we impose constraints on the free parameters. As expected, this solution recovers the electromagnetic-like Casimir solution for $m = 0$. Analyzing the traversability conditions, we graphically find that all will be satisfied for $ 0 \leq m \leq 0.20$. On the other hand, all the energy conditions are violated, as usual in this context. Stability from Tolman-Oppenheimer-Volkov (TOV) equation is guaranteed for all $r$ and from the speed of sound for $0.16 \le m \le 0.18$. Therefore, for $0.16 \leq m \leq 0.18$, we will have a stable solution that satisfies all traversability conditions.

gr-qc↗

arXiv2024

Meson scattering in a non-minimally Lorentz-violating scalar QED at finite temperature

In this paper we study meson scattering in a non-minimally Lorentz-violating scalar QED at finite temperature. The meson scatterings were investigated in tree level and the finite temperature effects were addressed by using the thermofield dynamics formalism. We have considered three types of scattering, namely, meson-antimeson of $a$-type into meson-antimeson of $b$-type, meson-antimeson of $a$-type into meson-antimeson of $a$-type and meson-meson of $a$-type into meson-meson of $a$-type. For each scattering we have computed the cross section in order to investigate the influence of the finite temperature effects.

hep-th↗

arXiv2024

Braneworlds in Warped Einsteinian Cubic Gravity

Einstenian cubic gravity (ECG) is a modified theory of gravity constructed with cubic contractions of the curvature tensor. This theory has the remarkable feature of having the same two propagating degrees of freedom of Einstein gravity (EG), at the perturbative level on maximally symmetric spacetimes. The additional unstable modes steaming from the higher order derivative dynamics are suppressed provided that we consider the ECG as an effective field theory wherein the cubic terms are seen as perturbative corrections of the Einstein-Hilbert term. Extensions of ECG have been proposed in cosmology and compact objects in order to probe if this property holds in more general configurations. In this work, we construct a modified ECG gravity in a five dimensional warped braneworld scenario. By assuming a specific combination of the cubic parameters, we obtained modified gravity equations of motion with terms up to second-order. For a thin 3-brane, the cubic-gravity corrections yield an effective positive bulk cosmological constant. Thus, in order to keep the 5D bulk warped compact, an upper bound of the cubic parameter with respect to the bulk curvature was imposed. For a thick brane, the cubic-gravity terms modify the scalar field potential and its corresponding vacuum. Nonetheless, the domain-wall structure with a localized source is preserved. At the perturbative level, the Kaluza-Klein (KK) tensor gravitational modes are stable and possess a localized massless mode provided the cubic corrections are small compared to the EG braneworld.

gr-qc↗

arXiv2023

Regular Black Holes in $D=2+1$ with $f(R)$ Gravity

Despite the experimental success of general relativity in the scales it has been tested, there are still some inconsistencies, such as explaining the acceleration of the universe and singularities. $f(R)$ gravity has emerged to provide corrections to the Ricci scalar, leading to new equations of motion that could explain this acceleration. On the other hand, Regular Black Holes, supported by non-linear electrodynamics, have well-defined curvature scalars but often violate energy conditions. In this work, we investigate how to obtain regular solutions in $(2+1)$ dimensions by considering $f(R)$ gravity and non-linear electrodynamics. Subsequently, we find that non-linear electrodynamics models that guarantee regular solutions in General Relativity do not produce regular solutions in $f(R)$ theory. Finally, we observe that energy conditions are still violated in $f(R)$ gravity.

gr-qc↗

arXiv2023

Lorentz-violating extension of scalar QED at finite temperature

In this work, we calculate the one-loop self-energy corrections to the gauge field in scalar electrodynamics modified by Lorentz-violating terms within the framework of the standard model extension (SME). We focus on both $CPT$-even and $CPT$-odd contributions. The kinetic part of the scalar sector contains a $CPT$-even symmetric Lorentz-breaking tensor, and the interaction terms include a vector contracted with the usual covariant derivative in a gauge-invariant manner. We computed the one-loop radiative corrections using dimensional regularization for both the $CPT$-even and $CPT$-odd cases. Additionally, we employed the Matsubara formalism to account for finite temperature effects.

hep-th↗

arXiv2023

5D Elko spinor field non-minimally coupled to nonmetricity in $f(Q)$ gravity

This paper aims to investigate the localization of the five-dimensional spinor field known as Elko (dual-helicity eigenspinors of the charge conjugation operator) by employing a Yukawa-like geometrical coupling in which the Elko field is non-minimally coupled to nonmetricity scalar $Q$. We adopt the braneworld scenarios in which the first-order formalism with sine-Gordon and linear superpotentials is employed to obtain the warp factors. A linear function supports the zero-mode trapping within the geometric coupling, leading to the same effective potential as the scalar field. Moreover, an exotic term must be added to obtain real-valued massive modes. Such modes are investigated through the Schrödinger-like approach.

gr-qc↗

arXiv2023

Localization of abelian gauge fields with Stueckelberg-like geometrical coupling on $f(T,B)$-thick brane

In the context of $f(T,B)$ modified teleparallel gravity, we investigate the influence of torsion scalar $T$ and boundary term $B$ on the confinement of both the gauge vector and Kalb-Ramond fields. Both fields require a suitable coupling in five-dimensional braneworld scenarios to yield a normalizable zero mode. We propose a Stueckelberg-like geometrical coupling that non-minimally couples the fields to the torsion scalar and boundary term. To set up our braneworld models, we use the first-order formalism in which two kinds of superpotential are taken: sine-Gordon and $ϕ^{4}$-deformed. The geometrical coupling is used to produce a localized zero mode. Moreover, we analyze the massive spectrum for both fields and obtain possible resonant massive modes. Furthermore, we do not find tachyonic modes leading to a consistent thick brane.

gr-qc↗

arXiv2023

Casimir effect in a Lorentz-violating tensor extension of a scalar field theory

This paper investigates the Casimir Energy modifications due to the Lorentz-violating CPT-even contribution in an extension of the scalar QED. We have considered the complex scalar field satisfying Dirichlet boundary conditions between two parallel plates separated by a small distance. An appropriate tensor parametrization allowed us to study the Casimir effect in three setups: isotropic, anisotropic parity-odd, and anisotropic parity-even. We have shown that the Lorentz-violating contributions promote increased Casimir energy for both the isotropic and anisotropic parity-odd configurations. However, in the parity-even case, the Lorentz-violating terms can promote either an increase or a decrease in the Casimir energy. We have shown that both the increased and decreased amounts in the Casimir energy depend on the momentum projection over the Lorentz-violating vectors.

hep-th↗

arXiv2022

A new class of regular black hole solutions with quasi-localized sources of matter in $(2 + 1)$ dimensions

This paper investigates a new class of regular black hole solutions in (2 + 1)-dimensions by introducing a generalization of the quasi-localized matter model proposed by Estrada and Tello-Ortiz. Initially, we try to physically interpret the matter source encoded in the energy-momentum tensor as originating from nonlinear electrodynamics. We show, however, that the required conditions for the quasi-locality of the energy density are incompatible with the expected behavior of nonlinear electrodynamics, which must tend to Maxwell's theory on the asymptotic limit. Despite this, we propose a generalization for the quasi-localized energy density that encompasses the existing models in the literature and allows us to obtain a class of regular black hole solutions exhibiting remarkable features on the event horizons and their thermodynamic properties. Furthermore, since the usual version of the first law of thermodynamics, due to the presence of the matter fields, leads to incorrect values of entropy and thermodynamics volume for regular black holes, we propose a new version of the first law for regular black holes.

gr-qc↗

arXiv2022

Softly higher-derivative massive gravity

In this work, we study the higher-derivative massive gravity in $D$-dimensional space-time with the mass term arisen due to a 2-brane embedded in a $4D$ Minkowski spacetime. We consider the effect of a resonance mass term from the DGP braneworld model for the higher-derivative massive gravity. Moreover, we add the gravitational Chern-Simons and Ricci-Cotton terms to this model and evaluate the graviton propagator using a basis of Barnes-Rivers spin projectors. Using the obtained propagator, we proceed with discussing the consistency of the model, writing the dispersion relations, and analyzing causality and unitarity.

hep-th↗

arXiv2022

Meson scattering in a Lorentz-violating scalar QED at finite temperature

This paper investigates how the nonzero temperature affects the differential cross-section for mesons scattering in a Lorentz-violating extension of the scalar electrodynamics. We initially discuss some features of the model and extract the zero temperature Feynman rules. Temperature effects are introduced using the Thermo Field Dynamics (TFD) formalism. It is shown that the corrections induced on the meson scattering are very large in the high-temperature regime. Furthermore, our results also suggest that temperature effects may contribute to new constraints on the Lorentz-violating parameters.

hep-ph↗

arXiv2022

Remarks on the effects of the quintessence on regular black holes

We present the generalization of a regular black hole surrounded by quintessence, considering Bardeen-like solutions added with this fluid. We also compare our solution particularized to the Bardeen one with those found in the recent literature, showing that some of them are inconsistent since they add quintessence "by hand", neglecting also the interesting behavior of the complete solution nearby the origin. Then, we present the correct way to implement the quintessential fluid in more general four-dimensional regular black hole geometries and explore some of its consequences, such as removing the black hole regularity at the origin.

gr-qc↗

arXiv2022

Exact solution for a traversable wormhole in a curvature-coupled antisymmetric background field

In this work, we study a traversable wormhole sourced by an ideal matter fluid with an antisymmetric 2-tensor background field coupled to gravity in a scenario of spontaneously broken Lorentz symmetry. Contrary to employed in the literature, we use a nonminimal curvature-coupling term $B^{μν}B^{κλ}R_{μνκλ}$ which incorporates all three kinds of Lorentz-violating coefficient for the pure-gravity sector of the minimal standard-model extension. We find that the wormhole is non-asymptotically globally flat and determine the allowed parameters of the theory, showing that the matter fluid must be necessarily anisotropic. We also analyze the energy conditions, checking their validity range and comparing them with those predicted by general relativity.

gr-qc↗

arXiv2022

Generalized Ellis-Bronikov traversable wormholes in $f(R)$ gravity with anisotropic dark matter

This paper studies generalized Ellis-Bronikov (E-B) traversable wormholes in $f(R)$ extended gravity. We assume that these wormholes are supported by anisotropic dark matter (DM) according to the most often used phenomenological models, namely those of Navarro-Frenk-White (NFW), Thomas-Fermi (T-F), and Pseudo-isothermal (PI). Initially, we obtain the field equations in a general scenario of $f(R)$ theories in the metric formalism for the static and spherically symmetric Morris-Thorne spacetime. Then we particularize to a $f(R)$ model with power-law, including the Starobinky modified gravity. Following, we analyze the energy conditions which are not dependent on the DM models (Null and Weak Energy Conditions -- NEC and WEC) and those which are model-dependent (Strong and Dominant Energy Conditions SEC and DEC). Finally, we compare some E-B wormhole solutions and the mentioned DM models, discussing the feasibility of the wormhole-dark matter system in different scenarios.

gr-qc↗

arXiv2022

Braneworlds in $f(Q)$ gravity

We propose a braneworld scenario in a modified symmetric teleparallel gravitational theory, where the dynamics for the gravitational field is encoded in the nonmetricity tensor rather than in the curvature. Assuming a single real scalar field with a sine-Gordon self-interaction, the generalized quadratic nonmetricity invariant $\mathbb{Q}$ controls the brane width while keeping the shape of the energy density. By considering power corrections of the invariant $\mathbb{Q}$ in the gravitational Lagrangian, the sine-Gordon potential is modified exhibiting new barriers and false vacuum. As a result, the domain wall brane obtains an inner structure, and it undergoes a splitting process. In addition, we also propose a non-minimal coupling between a bulk fermion field and the nonmetricity invariant $\mathbb{Q}$. Such geometric coupling leads to a massless chiral fermion bound to the 3-brane and a stable tower of non-localized massive states.

gr-qc↗