arXiv subjects

V. B. Bezerra

Publications and source records attributed to V. B. Bezerra.

At least 19 recordsLinked to original sources

arXiv2026

Neutrino oscillations in a Kalb-Ramond black hole background

The analysis examines how neutrinos behave when their trajectories unfold around a black hole sourced by a Kalb-Ramond field, where spontaneous Lorentz symmetry breaking reshapes the surrounding geometry. Instead of following the conventional order, the study focuses first on the observable consequences: alterations in the neutrino-antineutrino annihilation energy output, shifts in the oscillation phase accumulated along the path, and distortions in flavor conversion probabilities induced by gravitational lensing. These features are then tied to the Lorentz-violating spacetime structure, which governs the propagation of the neutrinos. Numerical simulations are carried out for both two- and three-flavor descriptions, with normal and inverted mass orderings.

gr-qc↗

arXiv2026

Exploring a phantom Dirac-Born-Infeld regular black hole via particle emission, wave scattering and geodesics

We examine particle creation, evaporation, scalar wave absorption and scattering, and geodesic motion in the asymptotically flat regular black hole supported by a phantom Dirac-Born-Infeld field. For massless bosonic and fermionic fields, the Bogoliubov transformations yield thermal spectra whose Hawking temperature decreases as the regular core becomes more prominent. Energy-conserving tunneling recovers the same temperature in the low-energy limit, whereas recoil and the DBI contribution introduce nonthermal corrections and suppress particle emission. In the high-frequency regime, the enlargement of the cross section does not compensate for the reduction in temperature, resulting in a lower luminosity and a longer evaporation time. A numerical partial wave analysis shows that the total scalar absorption increases with the regular core scale, approaches the horizon area at low frequencies, and oscillates around an enlarged geometric capture limit at high frequencies. The scattering phase shifts modify the multipolar amplitudes nonuniformly and displace the interference fringes toward larger angles. Furthermore, both null and timelike trajectories experience stronger deflection as the regular core contribution increases.

gr-qc↗

arXiv2026

A rotating black hole in a Hernquist dark matter halo: horizon geometry, thermodynamics, and quantum emission

We investigate the geometrical, thermodynamic, and quantum emission properties of a rotating black hole immersed in a Hernquist dark matter halo. Starting from a static black hole spacetime surrounded by a Hernquist distribution, we construct its rotating counterpart through the noncomplexification formulation of the Newman-Janis algorithm and analyze the modifications induced by the independent halo parameters $ρ$ and $r_s$ and the rotation parameter $a$. The horizon structure is determined from the roots of the radial function $Δ(r)$, while the stationary limit surfaces and the corresponding ergoregions are obtained from the condition $g_{tt}=0$. We show that the Hernquist contribution displaces the outer event horizon toward larger radii and modifies the size of the ergoregion, whereas rotation controls the oblateness of the horizon and the strength of frame dragging. We further derive the surface gravity, Hawking temperature, Bekenstein-Hawking entropy, and heat capacity. The quantum tunneling rate is obtained from the Hamilton-Jacobi method, leading to the corresponding occupation number and a thermal estimate of the particle creation density. Finally, we estimate the Hawking luminosity and evaporation timescales within a Stefan-Boltzmann approximation. All standard Kerr and Schwarzschild results are recovered in the appropriate limiting cases.

gr-qc↗

arXiv2026

Gravitational wave propagation in Hořava-Lifshitz gravity

We investigate the generation and propagation of gravitational waves in the leading parity-even infrared truncation of Hořava-Lifshitz gravity, characterized by the modified tensor dispersion relation $ω^{2}=k^{2}+αk^{4}$. Working in the transverse-traceless sector, we show that the higher-spatial-derivative correction preserves the conventional plus and cross polarizations and introduces neither polarization mixing, helicity splitting, nor gravitational birefringence. We construct the retarded Green function of the modified wave operator and derive the radiation-zone waveform to first order in $α$. The resulting signal exhibits a frequency-dependent amplitude renormalization together with a dispersive propagation phase that accumulates over the source-observer distance. We apply the formalism to a binary black hole system in a quasi-circular orbit and obtain the polarization waveforms for an arbitrary observation direction. We further derive the corresponding energy flux, total luminosity, and adiabatic chirp evolution. In terms of the observed gravitational wave frequency $f$, the leading corrections satisfy $Δh_{A}/h_{A}^{\mathrm{GR}}=-8π^{2}αf^{2}$ and $ΔP/P_{\mathrm{GR}} =Δ\dot{f}/\dot{f}_{\mathrm{GR}} =-16π^{2}αf^{2}$, while the accumulated generation phase has the frequency dependence of a relative third post-Newtonian contribution. By mapping the Hořava-Lifshitz coefficient to the LIGO-Virgo-KAGRA modified-dispersion parametrization, we obtain $-6.2\times10^{2}\,\mathrm{eV}^{-2} <α< 1.9\times10^{2}\,\mathrm{eV}^{-2}$ at $90\%$ credibility from the GWTC-4.0 posterior.

gr-qc↗

arXiv2026

Gauge-covariant Raychaudhuri dynamics for spin-nondegenerate Lorentz-violating congruences

We investigate the Raychaudhuri dynamics of charged spin-nondegenerate Lorentz-violating particle congruences under minimal electromagnetic coupling. The coupling is introduced through the gauge-covariant momentum $P_μ=π_μ-qA_μ$, so that the branch dispersion relation keeps its free functional form, while the electromagnetic field enters through the evolution of $P_μ$. For a generic branch $\mathcal D^{(\pm)}(P)$, the tangent $k^μ_{(\pm)}$ and the momentum Hessian $M^{μν}_{(\pm)}$ determine the covariant acceleration, $a^μ_{(\pm)}=-qM^{μν}_{(\pm)}F_{νρ}k^ρ_{(\pm)}$. As a consequence, the Raychaudhuri equation acquires the branch-dependent electromagnetic source $-q\nabla_μ\!\left(M^{μν}_{(\pm)}F_{νρ}k^ρ_{(\pm)}\right)$. We apply this construction to the $b_μ$, $H_{μν}$, and $d_{μν}$ sectors, obtaining the corresponding branch tangents, Hessians, accelerations, and focusing equations. In flat spacetime, the electromagnetic field modifies the expansion through the divergence of the effective branch force. Therefore, uniform fields may bend the trajectories, whereas local focusing requires field gradients or, in the magnetic case, a coupling to an already deformed congruence. We also develop the analogous description for semiclassical quasiparticle beams, where the band Hessian plays the role of an effective electromagnetic response tensor. For anisotropic parabolic, Dirac-like, and Weyl-type dispersions, the same geometric structure relates electromagnetic textures to beam focusing. In two-branch systems, the opposite Hessians of the branches can produce focusing in one congruence and defocusing in the other, giving a quasiparticle realization of branch-dependent birefringence.

gr-qc↗

arXiv2026

Shadows and lensing signatures of a rotating black hole in a Hernquist dark matter halo

We investigate the optical properties of a rotating black hole immersed in a Hernquist dark matter halo. The spacetime is generated from a static Hernquist black hole through the noncomplexification version of the Newman-Janis procedure, yielding a Kerr-like geometry whose halo contribution is encoded in the radial function $Δ(r)$ \cite{AraujoFilho:2026hernquist}. We derive the null geodesic equations, effective potentials, radial acceleration, and representative three-dimensional photon trajectories around the event horizon and ergoregion. Using the separability of the Hamilton-Jacobi equation, we obtain the critical impact parameters of unstable spherical photon orbits and construct the shadow contours for a distant observer. The rotation parameter mainly shifts and distorts the shadow, whereas the Hernquist halo enlarges the photon capture region and increases the apparent shadow size. Comparing the area-equivalent shadow diameter with the Event Horizon Telescope measurements of Sgr A$^\ast$ and M87$^\ast$, we constrain the dimensionless halo parameter $\hatρ=M^2ρ$. The strongest restriction comes from Sgr A$^\ast$, giving $\hatρ\sim(2.7-3.8)\times10^{-3}$ at $1σ$ and $\hatρ\sim(4.1-5.2)\times10^{-3}$ at $2σ$. We also analyze strong- and weak-field gravitational lensing. In the strong-field regime, the halo shifts the unstable photon orbit and critical impact parameter, controlling the logarithmic deflection angle and the position of relativistic images. In the weak-field regime, the halo contributes already to the leading bending angle and enhances deviations from Kerr as $ρ$ grows. From the Einstein ring of ESO325-G004, we further obtain $0\leq\hatρ\lesssim0.00939$ at $1σ$ and $0\leq\hatρ\lesssim0.01963$ at $2σ$.

gr-qc↗

arXiv2026

Lorentz-violating modifications to particle dynamics, thermodynamics and vacuum energy in bumblebee gravity

We investigate how spontaneous Lorentz symmetry breaking in bumblebee gravity modifies particle dynamics, thermodynamics, and vacuum energy around a static black hole background. Starting from the optical-mechanical correspondence, we derive a modified dispersion relation that encodes the influence of the Lorentz-violating parameter $λ$ on the propagation of massive and massless modes. We analyze the resulting optical properties, including the effective refractive index, group velocity, and energy-dependent time delay, and show how the non-asymptotically flat geometry reshapes signal propagation. From the same dispersion relation, we construct the interparticle potential for massive and massless excitations and evaluate the electron scattering cross section within the Born approximation, identifying characteristic Lorentz-violating corrections. We then develop a statistical-ensemble description based on the deformed energy-momentum relation and obtain analytic expressions for the thermodynamic observables of a massless bosonic gas. The pressure, mean energy, entropy, and heat capacity are examined in three representative regimes -- extremely close to the horizon, near the photon sphere, and in the asymptotic region -- where Lorentz violation systematically increase the magnitude of these quantities and leads to finite asymptotic plateaus. Finally, we analyze the vacuum state in the curved background and compute the regularized Casimir energy at zero and finite temperature.

gr-qc↗

arXiv2026

Gravitational Wave Signatures from Periodic Orbits around a Non--commutative Schwarzschild Black Hole

In this work, we investigate massive particle motion and the gravitational wave emission generated by periodic trajectories around a non--commutative \textit{Schwarzschild} black hole sourced by a Lorentzian matter distribution. We analyze the effective potential, the marginally bound orbit, and the innermost stable circular orbit, showing that non--commutative corrections shift these characteristic orbits toward smaller radii and reduce their corresponding angular momenta. The allowed region in the $(E, L)$ plane is also displaced toward lower values, favoring more tightly bound configurations. Periodic trajectories are classified through the rational parameter $q$, which relates the radial and azimuthal frequencies. For a fixed orbital topology, increasing the non--commutative parameter lowers the energy required to produce the orbit and results in more compact zoom--whirl configurations. Small deviations from the periodic energies are also shown to generate precessional drift. From the periastron advance of the S2 star around Sgr~A$^*$, we obtain the preliminary bound $Θ/M^{2}<0.014$. Finally, using the adiabatic and numerical kludge approximations, we compute the gravitational wave polarizations and find phase shifts and an overall enhancement of the amplitude.

gr-qc↗

arXiv2026

Gravitational aspects of a new bumblebee black hole

In this paper, we examine the physical consequences of a recently introduced black hole solution in bumblebee gravity [1]. The geometry is first presented and then reformulated through suitable coordinate adjustments, which make its global conical character evident. We then study the propagation of particles by solving the geodesic equations for null and timelike trajectories. The associated critical orbits (or photon spheres) are obtained, and shadow radius are computed and compared with other Lorentz-violating configurations in bumblebee and Kalb-Ramond models, including their charged and cosmological extensions. Massive particle motion is analyzed separately, followed by the construction of the effective potentials for scalar, vector, tensor, and spinor perturbations. These potentials allow the calculations of quasinormal frequencies and the corresponding time-domain evolution. Gravitational lensing phenomena are investigated in the weak and strong deflection regimes, and the light-travel time delay is also evaluated. The study concludes with bounds on the Lorentz-violating parameter based on classical Solar System experiments.

gr-qc↗

arXiv2026

Electromagnetic dynamics and geometric transport in spin-nondegenerate SME particles

We investigate the electromagnetic dynamics of spin-nondegenerate classical particle models arising from Lorentz-violating sectors of the Standard-Model Extension, focusing on the $b_μ$ background. Starting from the type-2 relativistic Lagrangian, we introduce minimal electromagnetic coupling and derive the exact Hamiltonian dynamics associated with each sector in terms of the gauge-covariant kinetic momentum. The modified dispersion relation leads to a sector-dependent relation between velocity and momentum, which directly affects the response to external fields. In the presence of a uniform magnetic field, we show that the two sectors exhibit distinct cyclotron frequencies and radii, implying that even constant fields dynamically resolve the underlying structure of the theory. In the nonrelativistic regime, the Lorentz-violating background induces a sector-dependent modification of the transverse inertial response, which can be interpreted as an effective anisotropic mass. After projection onto a single sector, the reduced dynamics acquires a noncanonical symplectic structure. The equations of motion can be written in semiclassical form with an effective momentum space curvature $Ω_{\pm}$, leading to anomalous velocity terms and a modified phase-space measure. As a consequence, a purely electric field generates opposite transverse drifts proportional to $q\,\mathbf{E} \times Ω_{\pm}$, producing a Hall-like current without requiring a magnetic field.

physics.gen-ph↗

arXiv2026

Frolov Black Hole Surrounded by a Cloud of Strings

We obtain the metric which describes the spacetime corresponding to the Frolov black hole in the presence of a cloud of strings and discuss how this cloud affects the regularity of the solution and the energy conditions. In addition, we analyze geodesics, effective potential, and several thermodynamic aspects. Finally, we compare our results with the corresponding findings in the literature for the original Frolov black hole, that is, in the absence of a cloud of strings

gr-qc↗

arXiv2025

Charged Hayward black hole with a cosmological constant and surrounded by quintessence and a cloud of strings

A family of exact solutions extending the Hayward black hole by incorporating multiple sources is obtained. The most comprehensive scenario describes a charged Hayward black hole with a cosmological constant, immersed in quintessence and accompanied by a cloud of strings. The study examines how the Kretschmann scalar varies with the parameters linked to the various sources and concludes with an analysis of the geodesics and the corresponding effective potential.

gr-qc↗

arXiv2025

Charged Bardeen black hole with a cosmological constant and surrounded by quintessence and a cloud of strings

Exact solutions which generalize the Bardeen black hole solution, in the sense that several sources are taken into account, are derived. The most general case corresponds to a charged Bardeen black hole with a cosmological constant and surrounded by quintessence and a cloud of strings. A discussion is presented concerning the Kretschmann scalar and its dependence with the parameters associated to the different sources. Finally, the geodesics and effective potential are analyzed.

gr-qc↗

arXiv2025

Gravitational signatures of a nonlinear electrodynamics in $f(R,T)$ gravity

In this work, we investigate a nonlinear electrodynamics model within the framework of $f(R,T)$ gravity. We begin by outlining the general features of the theory and analyzing the event horizon under conditions ensuring its real and positive definiteness. We then examine light trajectories, focusing on critical orbits, shadow radii, and geodesics of massless particles. The parameters $α$ and $β$, associated with the nonlinear extension of the Reissner-Nordström spacetime, are constrained using observational data from the Event Horizon Telescope (EHT). Subsequently, we analyze the thermodynamic properties of the system, including Hawking temperature, entropy, and heat capacity. Quasinormal modes are computed for scalar, vector, tensor, and spinorial perturbations, with the corresponding time-domain profiles explored as well. Gravitational lensing is then studied in both weak and strong deflection limits, along with the stability of photon spheres. Finally, we examine additional topological aspects, including topological thermodynamics and the topological photon sphere.

gr-qc↗

arXiv2025

The sound of quintessence: analogue Kiselev acoustic black holes

In this work, we demonstrate that the geometry of a spherically symmetric black hole surrounded by a Kiselev anisotropic fluid can be effectively mimicked by an experimental setup as the ones used to investigate some physical phenomena associated with acoustic black holes. Thus, we construct the metric describing Kiselev acoustic black holes by using the Gross--Pitaevskii theory and present a general analytical solution that encompasses, as particular cases, several classes of geometries associated with black holes. This unified framework allows for the description of a wide variety of analogue spacetimes, including new analogue geometries that have not been previously explored in the literature. Then, we examine the behavior of scalar field perturbations in this background by solving the massless Klein--Gordon equation. Depending on the boundary conditions between the acoustic event horizon and infinity, we obtain the quasinormal and quasibound spectra. This study opens up avenues for experimental investigation within the context of analog gravity models, by offering new possibilities to simulate and study black hole phenomena in laboratory settings.

gr-qc↗

arXiv2025

Some remarks on Frolov-AdS black hole surrounded by a fluid of string

A class of new solutions that generalizes the Frolov regular black hole solution is obtained. The generalization is performed by adding the cosmological constant and surrounding the black hole with a fluid of strings. Among these solutions, some preserve the regularity of the original Frolov solution, depending on the values of the parameter $β$, which labels the different solutions. A discussion is presented on the features of the solutions with respect to the existence or not of singularities, by examining the Kretschmann scalar, as well as by analysing the behavior of the geodesics concerning their completeness. It is performed some investigations concerning different aspects of thermodynamics, concerning the role played by the parameter associated with the Frolov regular black hole solution, as well as the parameter that codifies the presence of the fluid of strings. These are realized by considering different values of the parameter $β$, in particular, for $β=- 1/2$, in which case the regularity of the Frolov black hole is preserved. All obtained results closely align with the ones obtained by taking the appropriate particularizations.

gr-qc↗

arXiv2025

Black holes as gravitational mirrors

Retrolensing is a gravitational lensing effect in which light emitted by a background source is deflected by a black hole and redirected toward the observer after undergoing nearly complete loops around the black hole. In this context, we explore the possibility of seeing objects of the solar system in past eras through telescope observations by using black holes as a gravitational mirror. We consider the motion of the light around Reissner-Nordström space-time and discuss the properties of the trajectories of boomerang photons. It was shown that, depending on the angle of emission and the position of the source, the photons could return to the emission point. Afterward, we explore the possibility of considering the returning photons in retrolensing geometry where the observer is between the source and the lens in which two classes of black holes are explored: The supermassive Sgr A* black hole at the galactic center and a nearby stellar black hole. For the first time in the literature, we propose the study of the returning photons of planets instead of stars in retrolensing geometry.

gr-qc↗

arXiv2024

Some remarks on Hayward-AdS black hole surrounded by a fluid of strings

We obtain a class of solutions corresponding to a generalization of the Hayward black hole by solving the Einstein equations coupled to a particular nonlinear electromagnetic field. The generalization is realized by considering, additionally, the presence of the cosmological constant and a source corresponding to an anisotropic fluid, namely, a fluid of strings, that surrounds the black hole. We show that the obtained class of solutions preserves or does not the regularity of the original Hayward black hole solution, depending on the values of the parameter $β$ which labels the different solutions. We discuss the characteristics of the solutions, from the point of view of the singularities of spacetime, by examining the behavior of the Kretschmann scalar as well as of the geodesics concerning their completeness. We analyze some aspects of thermodynamics, particularizing one of the solutions obtained, namely, for $β=-1/2$, in which case the regularity of the Hayward black hole is preserved. Some thermodynamic quantities are obtained and analyzed, for example, pressure, heat capacity, and the critical points, and we show how these quantities change for different values of the parameter $q$ associated with the original Hayward solution, as well as with the parameter $b$ associated with the presence of the fluid of strings. The phase transitions are also analyzed by using the equation of state and the Gibbs free energy.

gr-qc↗