arXiv subjects

Leandro A. Lessa

Publications and source records attributed to Leandro A. Lessa.

8 recordsLinked to original sources

arXiv2026

Thin-Shell Black Bounce

A recently proposed class of black-bounce solutions sourced by anisotropic fluids, whose exterior reproduces the Reissner-Nordström geometry all the way down to a minimal-area bounce, was put forward by Lessa and Olmo. In this work, we show that this solution conceals a thin-shell structure precisely at the bounce. Motivated by this observation, we construct a new class of black-bounce solutions with static, spherical symmetry featuring the emergence of a minimal-area bounce supported by a thin shell. This nontrivial topological structure is shown to arise from the degeneracy of the metric at the bounce, where the inverse metric becomes ill-defined, leading to curvature tensors with distributional discontinuities precisely at that point. As a consequence, a delta-function thin shell of energy-condition-violating matter is necessarily present at the bounce. To generate such solutions, we draw on proposals from quantum gravity that predict the existence of a fundamental minimum length scale, employing energy density profiles that encode these quantum-gravitational effects in an effective manner, replacing the point-like description of matter at minimal-length scales with a smeared one. We consider two well-motivated profiles, of Lorentzian and Gaussian type, to generate a novel class of solutions exhibiting the features of either regular black holes or wormholes, whose center conceals a thin-shell bounce. In addition, we investigate the thermodynamics of these compact objects.

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.

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arXiv2026

Non-minimal matter sector couplings in Lorentz-violating gravity: Self-consistent traversable wormholes and quasinormal modes

The anisotropies induced by Lorentz-violating fields pose significant challenges for the search for compact objects in non-vacuum environments. In this work, nevertheless, we demonstrate that introducing couplings between Lorentz-violating fields and matter allows a remarkable class of spacetimes: traversable wormholes. Specifically, we consider additional couplings in the Lagrangian of a phantom scalar field and derive Ellis-Bronnikov spacetime analogs in a Lorentz-violating scenario where both a vector field and an antisymmetric rank-2 tensor field spontaneously acquire non-zero vacuum expectation values. Despite the distinct nature of these fields, their non-zero vacuum expectation values contribute additively to the overall effect on the phantom distribution and on the resulting line element. Moreover, to probe the effects of the Lorentz violation in these spacetimes, we consider scalar perturbations lying in these spacetimes either coupled to the Lorentz-violating fields or minimally coupled to the metric. Notably, the additional Lorentz-violating couplings can alter scalar field dynamics so that perturbations propagate as if in a General Relativity background, thereby allowing for some traits of Lorentz violation to remain hidden. We compute the quasinormal mode spectra of these perturbations using three methods: direct integration, the 6th-order WKB approximation, and the Prony method, finding strong agreement among the results.

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arXiv2025

Black holes in higher-derivative Weyl conformal gravity

We obtain exact black hole solutions for static and spherically symmetric sources in a Weyl conformal gauge theory of gravity. We consider a quadratic gravitational action built from the Weyl tensor within a dilation geometry. In a post-Riemannian formulation, we derive a Weyl conformal action for a scalar-vector-tensor theory, where the scalar degree of freedom originates from the high-curvature terms and the vectorial one stems from the Weyl non-metricity condition. Adopting a static, spherically symmetric geometry, the vacuum field equations for the gravitational, scalar, and Weyl fields are obtained. Under these conditions, we find a Mannheim-Kazanas-type black hole solution, whose Rindler acceleration term depends on the Weyl gauge coupling constant. Furthermore, we show that the original theory can recover the Einstein-Hilbert action with a positive cosmological constant plus a higher-derivative term with Horndeski-like terms through a spontaneous symmetry breaking triggered by the vacuum expectation value of the scalar field. The new solution in the theory without conformal symmetry presents new terms introduced by the residual Weyl symmetry corrections. We demonstrate that in a regime where the Planck mass suppresses the higher-derivative term, the Rindler term persists in the low-energy limit.

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arXiv2025

On the self-consistency of compact objects in Lorentz-violating gravity theories

Self-consistent solutions in Lorentz-violating gravity theories require the simultaneous satisfaction of: (i) the corresponding Einstein field equations, (ii) the matter field equations, and (iii) the Lorentz-violating field equations. In vacuum states, the dynamics of Lorentz-violating tensor fields may reduce to geometric constraints, potentially precluding entire classes of compact objects. These constraints are crucial for ensuring physical consistency in Lorentz-violating frameworks, as they eliminate metric families incompatible with the anisotropies induced by spontaneous Lorentz symmetry breaking. We investigate the criteria governing the emergence of these geometric constraints and analyze their consequences. Our analysis establishes a consistency framework for evaluating compact objects in these theories, demonstrating that several previously reported solutions in Lorentz-violating gravity models are physically inadmissible.

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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.

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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.

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arXiv2025

Wormholes in Lorentz-violating gravity

We investigate the possibility of obtaining traversable wormholes supported by phantom scalar fields in Lorentz-violating gravity with an antisymmetric rank-2 tensor with a non-zero vacuum expectation value non-minimally coupled to the curvature tensor. This Lorentz violation framework shows to be a suitable scenario to search for wormhole solutions in the presence of Lorentz violation, since it introduces mild constraints on the areal radius. The vacuum expectation value of the antisymmetric rank-2 tensor, nonetheless, imposes constraints on the lapse function. As a consequence, under the vacuum configuration adopted, the allowed lapse functions can be either constant, linear or quadratic, depending on the self-interaction potential that drives the spontaneous breaking of the Lorentz symmetry. Thus, we find the Ellis-Bronnikov counterpart in this Lorentz-violating scenario as well as Lorentz-violating wormholes with a Rindler-type acceleration and an effective cosmological constant. Properties of these wormholes, such as their non-flat asymptotics, are investigated.

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