arXiv subjects

R. D. B. Fontana

Publications and source records attributed to R. D. B. Fontana.

12 recordsLinked to original sources

arXiv2026

Quasinormal modes of a quantum inspired black hole in four dimensions with cosmological constant

We study the scalar and Dirac perturbations of quantum-corrected black holes with cosmological constant. Using two different methods (WKB and double-null characteristic integration) we compute the quasinormal modes (QNMs) of de Sitter and Anti-de Sitter solutions considering linear field perturbations in the background geometry. In the limit of general relativity black holes our methods demonstrate good convergence with the available results in literature. In the presence of an extra quantum parameter we verify that all perturbations are stable evolving in towers of quasinormal oscillations. We scrutinize the spectra of both dS and AdS solutions studying the influence of that extra parameter in the frequencies.

gr-qc↗

arXiv2024

Accelerated black holes in (2+1) dimensions: Quasinormal modes and Stability

We investigate the propagation of a scalar field in a $(2+1)$-dimensional accelerated black hole, recently revisited in \cite{Arenas_Henriquez_2022}. We briefly describe the minimally-coupled configuration as rendering a trivial scalar perturbation with a rescale of the field mass. On the contrary, the free scalar field propagation presents an intricate dynamic, whose equation may be reduced through the use of Israel junction conditions and a non-trivial ansatz. In this case, using two different methods we calculate the quasinormal modes of the solution also obtaining unstable field profiles delivered by the linear scalar perturbation to the background geometry. We scrutinize the parameter space of angular eigenvalue of the field and accelerations under which such instabilities happen.

gr-qc↗

arXiv2024

Aspects of regular and singular electromagnetic-generalized-quasitopological-gravities black holes in (2+1) dimensions

We investigate quasitopological black holes in $(2+1)$ dimensions in the context of electromagnetic-generalized-quasitopological-gravities (EM-GQT). For three different families of geometries of quasitopological nature, we study the causal structure and their response to a probe scalar field. To linear order, we verify that the scalar field evolves stably, decaying in different towers of quasinormal modes. The studied black holes are either charged geometries (regular and singular) or a regular Bañados-Teitelboim-Zanelli (BTZ)-like black hole, both coming from the EM-GQT theory characterized by nonminimal coupling parameters between gravity and a background scalar field. We calculate the quasinormal modes applying different numerical methods with convergent results between them. The oscillations demonstrate a very peculiar structure for charged black holes: in the intermediate and near extremal cases, a particular scaling arises, similar to that of the rotating BTZ geometry, with the modes being proportional to the distance between horizons. For the single horizon black hole solution, we identify the presence of different quasinormal families by analyzing the features of that spectrum. In all three considered geometries, no instabilities were found.

gr-qc↗

arXiv2022

Gauss-Bonnet black holes in (2+1) dimensions: Perturbative aspects and entropy features

We investigate some aspects of the $(2+1)$-dimensional Gauss-Bonnet black hole proposed in [1][2]. The perturbations of scalar and massless spinorial fields are studied suggesting the dynamical stability of the geometry. The field evolution is analyzed calculating the quasinormal modes for different parameters and exploring the influence of the coupling constant of the theory. The hydrodynamical modes are also obtained in the small coupling limit. Furthermore, the entropy bound and the dominant semiclassical correction to the black hole entropy are calculated.

gr-qc↗

arXiv2021

Superradiance and instabilities in black holes surrounded by anisotropic fluids

In this paper we analyze the propagation of a charged scalar field in a Reissner-Nordström black hole endowed with one anisotropic fluid that can play the role of a cosmological term for certain set of parameters. The evolution of a scalar wave scattering is examined giving rise to the same superradiant scattering condition as in the de Sitter case. In addition, an analysis of the modes coming from the application of quasinormal boundary conditions is presented. Some special cases displaying analytical solutions for the quasinormal frequencies are discussed. Moreover, the superradiant condition is adapted to the quasinormal problem triggering unstable modes, what is confirmed by our numerical analysis.

gr-qc↗

arXiv2021

Anomalous decay rate of quasinormal modes in Reissner-Nordström black holes

The anomalous decay rate of the quasinormal modes occurs when the longest-lived modes are the ones with higher angular number. Such behaviour has been recently studied in different static spacetimes, for scalar and fermionic perturbations, being observed in both cases. In this work, we extend the existent studies to the charged spacetimes, namely, the Reissner-Nordström, the Reissner-Nordström-de Sitter and the Reissner-Nordström-Anti-de Sitter black holes. We show that the anomalous decay rate behaviour of the scalar field perturbations is present for every charged geometry in the photon sphere modes, with the existence of a critical scalar field mass whenever $Λ\geq 0$. In general, this critical value of mass increases with the raise of the black hole charge, thus rendering a minimum in the Schwarzschild limit. We also study the dominant mode/family for the massless and massive scalar field in these geometries showing a non-trivial dominance of the spectra that depends on the black hole mass and charge.

gr-qc↗

arXiv2020

Analytical correspondence between shadow radius and black hole quasinormal frequencies

We consider the equivalence of quasinormal modes and geodesic quantities recently brought back due to the black hole shadow observation by Event Horizon Telescope. Using WKB method we found an analytical relation between the real part of quasinormal frequencies at the eikonal limit and black hole shadow radius. We verify this correspondence with two black hole families in $4$ and $D$ dimensions, respectively.

gr-qc↗

arXiv2020

Late-time tails, entropy aspects, and stability of black holes with anisotropic fluids

In this work we consider black holes surrounded by anisotropic fluids in four dimensions. We first study the causal structure of these solutions showing some similarities and differences with Reissner-Nordström-de Sitter black holes. In addition, we consider scalar perturbations on this background geometry and compute the corresponding quasinormal modes. Moreover, we discuss the late-time behavior of the perturbations finding an interesting new feature, i.e., the presence of a subdominant power-law tail term. Likewise, we compute the Bekenstein entropy bound and the first semiclassical correction to the black hole entropy using the brick wall method, showing their universality. Finally, we also discuss the thermodynamical stability of the model.

gr-qc↗

arXiv2019

Dynamical evolution of non-minimally coupled scalar field in spherically symmetric de Sitter spacetimes

We investigate the dynamical behavior of a scalar field non-minimally coupled to Einstein's tensor and Ricci scalar in geometries of asymptotically de Sitter spacetimes. We show that the quasinormal modes remain unaffected if the scalar field is massless and the black hole is electrically chargeless. In the massive case, the coupling of both parameters produces a region of instability in the spacetime determined by the geometry and field parameters. In the Schwarzschild case, every solution for the equations of motion with $\ell>0$ has a range of values of the coupling constant that produces unstable modes. The case $\ell=0$ is the most unstable one, with a threshold value for stability in the coupling. For the charged black hole, the existence of a range of instability in $η$ is strongly related to geometry parameters presenting a region of stability independent of the chosen parameter.

gr-qc↗

arXiv2019

Instability of Reissner-Nordström-AdS black hole under perturbations of a scalar field coupled to Einstein tensor

We study the instability of a Reissner-Nordström-AdS (RNAdS) black hole under perturbations of a massive scalar field coupled to Einstein tensor. Calculating the potential of the scalar perturbations we find that as the strength of the coupling of the scalar to Einstein tensor is increasing, the potential develops a negative well outside the black hole horizon, indicating an instability of the background RNAdS. We then investigate the effect of this coupling on the quasinormal modes. We find that there exists a critical value of the coupling which triggers the instability of the RNAdS. We also find that as the charge of the RNAdS is increased towards its extremal value, the critical value of the derivative coupling is decreased.

gr-qc↗

arXiv2018

Three-dimensional black holes with quintessence

We study a quintessential black hole solution in three dimensions, with mass and quintessence charge. By exploring the Carter-Penrose diagram, we show the presence of spacelike and lightlike singularities in the metric, given different values for the quintessence parameter, as well as an AdS-like spatial infinity and event horizon encapsulating the singularity. We also study the propagation of scalar and Dirac (Weyl) fields around the black hole solutions with different quintessence charges obtaining the quasinormal spectra for both fields using two different numerical methods with good agreement between the data. In both cases, the presence of quintessence increases the imaginary part of the quasinormal mode, since this is related to the event horizon of the solution, preserving the interpretation of this quantity as relaxation time in the corresponding CFT. We also investigate the behavior of high-temperature scalar field modes, demonstrating the presence of the so-called hydrodynamical limit, differently from the BTZ black hole, for which no such modes exist.

gr-qc↗

arXiv2007

Quasinormal modes of black holes immersed in a strong magnetic field

We found quasinormal modes, both in time and frequency domains, of the Ernst black holes, that is neutral black holes immersed in an external magnetic field. The Ernst solution reduces to the Schwarzschild solution, when the magnetic field vanishes. It is found that the quasinormal spectrum for massless scalar field in the vicinity of the magnetized black holes acquires an effective "mass" $μ= 2 B m$, where m is the azimuthal number and B is parameter describing the magnetic field. We shall show that in the presence of a magnetic field quasinormal modes are longer lived and have larger oscillation frequencies. The perturbations of higher dimensional magnetized black holes by Ortaggio and of magnetized dilaton black holes by Radu are considered.

hep-th↗