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Roberto V. Maluf

Publications and source records attributed to Roberto V. Maluf.

18 recordsLinked to original sources
arXiv2026

Bounds on Black Bounces from Phenomenological Imprints

In this work, we derive phenomenological constraints on a symmetric black-bounce geometry supported by an anisotropic fluid. We investigate the effects of the bounce parameter and the matter parameter on classical and strong-field observables, considering the perihelion advance, light deflection, Shapiro time delay, and black-hole shadow. In the weak-field regime, we obtain analytical corrections to the corresponding general-relativistic predictions and use Solar-System measurements to constrain the parameter space. We find that the matter parameter is generally constrained more strongly than the minimum-radius scale, reflecting the suppressed dependence of weak-field observables on the bounce parameter. In the strong-field regime, we show that the asymptotic shadow radius depends directly on the matter parameter, whereas the bounce parameter enters through the existence condition of the outer unstable photon orbit rather than through an independent correction to the shadow size. These results highlight the distinct roles played by the matter and bounce parameters in weak- and strong-field observables and provide complementary constraints on the parameter space of the symmetric black-bounce geometry.

gr-qc↗
arXiv2026

Shadows and gravitational perturbations of black bounces

We investigate axial gravitational perturbations and shadow formation in black-bounce geometries supported by anisotropic fluids within general relativity. Two distinct classes of solutions are analyzed: a symmetric Simpson--Visser-like black bounce and an asymmetric deformation of the Reissner--Nordström metric, which can feature either a bounded interior region or an unbounded wormhole-like extension. Our findings indicate that configurations with horizons, whether symmetric or asymmetric, exhibit single-barrier effective potentials and quasinormal frequencies nearly indistinguishable from those of standard black holes. In contrast, horizonless symmetric configurations may develop multiple potential barriers, giving rise to gravitational-wave echoes whose amplitude and separation depend sensitively on the bounce parameter $a$ and the density parameter $ρ_0$. Horizonless asymmetric solutions, on the other hand, exhibit regularized effective potentials that do not produce echoes and remain phenomenologically close to the Reissner--Nordström case. From the optical perspective, both classes of solutions with horizons exhibit a single relevant photon sphere and shadow profiles nearly indistinguishable from those of their black-hole counterparts, while horizonless symmetric configurations can sustain multiple photon rings. Horizonless asymmetric configurations may instead support either a single photon ring or none. Finally, we recover the standard eikonal correspondence between quasinormal modes and the instability of circular null geodesics for configurations with horizons. For horizonless geometries, however, the emergence of multiple potential barriers prevents a straightforward extension of this relation, although the strong similarity between the wave and optical sectors suggests that a meaningful phenomenological correspondence may still persist.

gr-qc↗
arXiv2026

Nonlocal Rarita-Schwinger theory

In this paper, one constructs a nonlocal extension of the Rarita-Schwinger theory for spin-$3/2$ fermions. Two classes of analytic form factors are considered: scalar form factors $f(\Box)$ and Dirac-operator form factors $f(\slashed{\partial})$. The massless theory is treated together with a covariant nonlocal gauge fixing, which allows the propagator to be written directly in terms of the spin-$3/2$ projector. In the massive theory, we show that the free Rarita-Schwinger constraints remain intact for analytic form factors, so that the unphysical spin-$1/2$ sector does not become dynamical. For $f(\Box)$ the tensor-spinor structure of the propagator is the same as in the local theory, while the pole equation is deformed by the scalar form factor. For $f(\slashed{\partial})$ the physical modes obey a nonlocal Dirac-type equation, leading to modified dispersion relations that can be written explicitly for exponential form factors. We discuss the conditions under which the construction is ghost-free at the free level and identify the natural limitations that must be addressed before interactions are introduced.

hep-th↗
arXiv2026

Duality in $SIM(2)$ topologically massive models with $B\wedge F$ term

This paper aims to investigate the classical duality between the $SIM(2)$-Maxwell-Kalb-Ramond (MKR) theory and a self-dual non-gauge-invariant model. First, we establish the equivalence in the free-field case using two complementary methods: a direct comparison of the equations of motion and the master Lagrangian approach. In both methodologies, we verify that the classical correspondence between the MKR model and self-dual fields exhibits modifications induced by very special relativity (VSR). Moreover, we employ the master Lagrangian approach to examine the duality when the self-dual model is minimally coupled to fermionic matter. We show that the resulting MKR model contains Thirring-like interactions modified by nonlocal contributions arising from VSR.

hep-th↗
arXiv2025

Braneworlds in Einstein-Scalar-Gauss-Bonnet gravity

We explore the features of a thick braneworld model in five dimensions governed by a Einstein-Gauss-Bonnet gravity with a non-minimal coupling to a dynamical scalar field. We consider two possible scalar-GB coupling function $χ(ϕ)$, one parity-even and another parity-odd function of the scalar field $ϕ$. For both choices, the scalar-Gauss-Bonnet non-minimal coupling produces a warped asymptotically $AdS_5$ spacetime even in the absence of a bulk cosmological constant. Outside the brane core, a negative cosmological constant is bounded by the scalar-GB coupling function. For a thick 3-brane configuration, we found solutions with localized brane energy density and pressure that dynamically produce a bulk cosmological constant. The corresponding scalar field solutions exhibit a non-topological (domain wall) behavior. In order to probe the 3-brane stability solution, we employed a perturbative analysis, by perturbing the thick brane solutions up to first-order. The Kaluza-Klein (KK) tensorial gravitational modes possess a localized massless mode and a tower of non-tachyonic diverging massive modes, what renders the solutions stable at least at the perturbative level.

gr-qc↗
arXiv2025

Echoes and quasinormal modes of asymmetric black bounces

We study quasinormal modes and echoes of symmetric and asymmetric black bounce solutions generated by anisotropic fluids within the framework of general relativity. We derive the effective potential governing massless scalar fields and compute the corresponding quasinormal mode spectra using three independent methods: sixth-order WKB, Pöschl-Teller and time-domain evolution. Our results show that symmetric black bounce configurations with horizons yield a standard single-barrier potential, while horizonless solutions may exhibit multiple potential barriers that generate gravitational wave echoes. These echoes are sensitive to model parameters such as the fluid energy density and the regularizing parameter $a$ that defines the minimal $2$-sphere. The asymmetric models considered recover the Reissner-Nordström solution in their external region but can be bounded or unbounded in the inside, depending on the sign of a parameter. Both cases have similar qualitative properties as far as wave emission is concerned but show no echoes. This makes it very difficult to distinguish them from standard Reissner-Nordström configurations.

gr-qc↗
arXiv2025

Regular black hole solutions in $(2 + 1)$-dimensional $f(R,T)$ gravity coupled to nonlinear electrodynamics

In this paper, we investigate regular black hole solutions in the (2+1)-dimensional versions of General Relativity and $f(R, T)$ gravity, both coupled to nonlinear electrodynamics. By admitting that the matter content that generates such geometries satisfies the Maxwell limit condition, we obtain a class of regular black holes that give rise to new solutions and successfully reproduce particular cases found in earlier studies of (2+1)-dimensional General Relativity. Moreover, we discover the first regular black hole solutions in (2+1)-dimensional $f(R, T)$ gravity and explore both qualitatively and quantitatively the non-conservation of the energy-momentum tensor present in those solutions.

gr-qc↗
arXiv2025

Thick braneworld in $f(Q,\mathcal{T})$ gravity

In this work, we study a codimension-one thick brane within the framework of $f(Q,\mathcal{T})$ modified symmetric teleparallel gravity, where $Q$ is the nonmetricity scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor. Using two specific choices of the warp factor, we construct the complete brane system, including the scalar field solution and energy density. We show how nonmetricity influences the brane profile and analyze the stability of the braneworld scenarios under small tensor perturbations.

gr-qc↗
arXiv2024

Geometrical deformation of brane matter field within $f(R,Q,P)$ gravity

In the context of braneworld scenarios, the real scalar field plays a crucial role by providing thickness for brane. In this work, we investigate a codimension-one thick brane within the framework of $f(R,Q,P)$ gravity, where $R$ represents the curvature scalar, while $Q=R_{μν}R^{μν}$ and $P=R_{μναβ}R^{μναβ}$ are quadratic geometric invariants. Our interest is to investigate the influence of these invariants on the scalar field solution and the energy density of the brane. Furthermore, we analyze the localization of spin $1/2$ fermions and the gravitino by employing a Yukawa-like coupling with the scalar field background. Such a coupling is able to produce a normalizable zero-mode for both fields.

gr-qc↗
arXiv2024

Nonsingular, lump-like, scalar compact objects in $(2+1)$-dimensional Einstein gravity

We study the space-time geometry generated by coupling a free scalar field with a non-canonical kinetic term to General Relativity in $(2+1)$ dimensions. After identifying a family of scalar Lagrangians that yield exact analytical solutions in static and circularly symmetric scenarios, we classify the various types of solutions and focus on a branch that yields asymptotically flat geometries. We show that the solutions within such a branch can be divided in two types, namely, naked singularities and nonsingular objects without a center. In the latter, the energy density is localized around a maximum and vanishes only at infinity and at an inner boundary. This boundary has vanishing curvatures and cannot be reached by any time-like or null geodesic in finite affine time. This allows us to consistently interpret such solutions as nonsingular, lump-like, static compact scalar objects, whose eventual extension to the $(3+1)$-dimensional context could provide structures of astrophysical interest.

gr-qc↗
arXiv2023

Duality between the Maxwell-Chern-Simons and self-dual models in very special relativity

This work aims to investigate the classical-level duality between the $SIM(1)$-Maxwell-Chern-Simons (MCS) model and its self-dual counterpart. Initially, our focus is on free-field cases to establish equivalence through two distinct approaches: comparing the equations of motion and utilizing the master Lagrangian method. In both instances, the classical correspondence between the self-dual field and the MCS dual field undergoes modifications due to very special relativity (VSR). Specifically, duality is established only when the associated VSR-mass parameters are the same. Furthermore, we analyze the duality when the self-dual model is minimally coupled to fermions. As a result, we show that Thirring-like interactions, corrected for non-local VSR contributions, are included in the MCS model. Additionally, we demonstrate the equivalence of the fermion sectors in both models, thereby concluding the proof of classical-level duality.

hep-th↗
arXiv2023

Yang-Mills Casimir wormholes in $D=2+1$

This work presents new three-dimensional traversable wormhole solutions sourced by the Casimir density and pressures related to the quantum vacuum fluctuations in Yang-Mills (Y-M) theory. We begin by analyzing the noninteracting Y-M Casimir wormholes, initially considering an arbitrary state parameter $ω$ and determine a simple constant wormhole shape function. Next, we introduce a new methodology for deforming the state parameter to find well-behaved redshift functions. The wormhole can be interpreted as a legitimate Casimir wormhole with an expected average state parameter of $ω=2$. Then, we investigate the wormhole curvature properties, energy conditions, and stability. Furthermore, we discover a novel family of traversable wormhole solutions sourced by the quantum vacuum fluctuations of interacting Yang-Mills fields with a more complex shape function. Deforming the effective state parameter similarly, we obtain well-behaved redshift functions and traversable wormhole solutions. Finally, we examine the energy conditions and stability of solutions in the interacting scenario and compare to the noninteracting case.

gr-qc↗
arXiv2023

One-loop radiative corrections in bumblebee-Stueckelberg model

This work aims to study the radiative corrections in a vector model with spontaneous Lorentz symmetry violation, known in the literature as the bumblebee model. We consider such a model with self-interaction quadratic smooth potential responsible for spontaneous Lorentz symmetry breaking. The spectrum of this model displays a transversal nonmassive mode, identified as Nambu-Goldstone, and a massive longitudinal mode. Besides the Lorentz symmetry, this model also exhibits gauge symmetry violation. To restore the gauge symmetry, we introduce the Stueckelberg field and calculate the two-point function by employing the principal-value (PV) prescription. The result is nontransversal, leading to a massive excited mode.

hep-th↗
arXiv2023

Vacuum polarization and induced Maxwell and Kalb-Ramond effective action in very special relativity

This work investigates the implications of very special relativity (VSR) on the calculation of vacuum polarization for fermions in the presence of Maxwell and Kalb-Ramond gauge fields in four-dimensional spacetime. We derive the $SIM(2)$-covariant gauge theory associated with an Abelian antisymmetric 2-tensor and its corresponding field strength. We demonstrate that the free VSR-Kalb-Ramond electrodynamics is equivalent to a massive scalar field with a single polarization. Furthermore, we determine an explicit expression for the effective action involving Maxwell and Kalb-Ramond fields due to fermionic vacuum polarization at one-loop order. The quantum corrections generate divergences free of nonlocal terms only in the VSR-Maxwell sector. At the same time, we observe UV/IR mixing divergences due to the entanglement of VSR-nonlocal effects with quantum higher-derivative terms for the Kalb-Ramond field. However, in the lower energy limit, the effective action can be renormalized like in the Lorentz invariant case.

hep-th↗
arXiv2019

Maxwell electrodynamics modified by a CPT-odd dimension-five higher-derivative term

In this paper, we consider an electrodynamics of higher derivatives coupled to a Lorentz-violating background tensor. Specifically, we are interested in a dimension-five term of the CPT-odd sector of the nonminimal Standard-Model Extension. By a particular choice of the operator $\hat{k}_{AF}$, we obtain a higher-derivative version of the Carroll-Field-Jackiw (CFJ) term, $\frac{1}{2}ε^{κλμν}A_λD_κ\square F_{μν}$, with a Lorentz-violating background vector $D_κ$. This modification is subject to being investigated. We calculate the propagator of the theory and from its poles, we analyze the dispersion relations of the isotropic and anisotropic sectors. We verify that classical causality is valid for all parameter choices, but that unitarity of the theory is generally not assured. The latter is found to break down for certain configurations of the background field and momentum. In an analog way, we also study a dimension-five anisotropic higher-derivative CFJ term, which is written as $ε^{κλμν}A_λT_κ(T\cdot\partial)^{2}F_{μν}$ and is directly linked to the photon sector of Myers-Pospelov theory. Within the second model, purely timelike and spacelike $T_κ$ are considered. For the timelike choice, one mode is causal, whereas the other is noncausal. Unitarity is conserved, in general, as long as the energy stays real - even for the noncausal mode. For the spacelike scenario, causality is violated when the propagation direction lies within certain regimes. However, there are particular configurations preserving unitarity and strong numerical indications exist that unitarity is guaranteed for all purely spacelike configurations. The results improve our understanding of nonminimal CPT-odd extensions of the electromagnetic sector.

hep-th↗
arXiv2018

Effects of spontaneous Lorentz violation in gravitational waves solutions

Gravitational wave solutions with spontaneous Lorentz symmetry breaking are studied. This breaking is triggered by a vector field, known as the bumblebee field. A brief analysis of the main consequences of this symmetry breaking on free-waves solutions and in the presence of matter sources are presented. For the free case, the modified wave equation for the gravitational perturbation field is solved, and we compare the polarization states with the usual solution. Considering a current that acts as a source of the radiation, we solve the equation of motion using the Green function method. Finally, considering that the source has slow motion, we derive the new quadrupole formula.

hep-th↗
arXiv2012

Noncommutative Space Corrections on the Klein-Gordon and Dirac Oscillators Spectra

We consider the influence of a noncommutative space on the Klein-Gordon and the Dirac oscillators. The nonrelativistic limit is taken and the $θ$-modified Hamiltonians are determined. The corrections of these Hamiltonians on the energy levels are evaluated in first-order perturbation theory. It is observed a total lifting of the degeneracy to the considered levels. Such effects are similar to the Zeeman splitting in a commutative space.

hep-th↗