arXiv subjects

Omar Pedraza

Publications and source records attributed to Omar Pedraza.

18 recordsLinked to original sources

arXiv2026

Scattering and absorption sections by an improved Schwarzschild black hole

In this contribution, we investigate the scattering and absorption sections of the improved Schwarzschild black hole. The differential scattering section is analysed using three complementary approaches: the classical approximation, the semi-classical approximation, and the partial wave technique. We show that, while the classical scattering section exhibits only small deviations from the standard Schwarzschild case, the semi-classical and partial wave analyses reveal differences in the interference pattern and in the amplitude. Also, the absorption section is computed using the partial wave method and compared with the sinc approximation. We find that both approaches present deviations that appear in the low-frequency regime, where the partial wave result approaches the horizon area. Our results indicate that quantum corrections in the Schwarzschild can lead to modifications in scattering and absorption properties, providing further insight into the phenomenology of quantum corrected black holes.

gr-qc↗

arXiv2026

Scattering sections from regular black holes immersed in perfect fluid dark matter

In this contribution, we investigate the scattering cross sections of black holes immersed in perfect fluid dark matter (PFDM). We present both the classical and semi-classical scattering cross sections for different values of the parameter that characterizes the PFDM contribution. Our results show that the presence of dark matter increases the classical scattering cross section and modifies the width of the interference fringes in the semi-classical regime. In addition, the scattering cross section is also computed using the partial wave method for the black holes considered, exhibiting similar qualitative behavior. These findings suggest that the effects of dark matter surrounding black holes may play an important role in black holes phenomenology, particularly in certain regions near the black hole.

gr-qc↗

arXiv2025

Quasi-normal modes of the Ay\'on-Beato-Garc\'ia black hole surrounded by quintessence

We compute the quasi-normal modes of scalar, electromagnetic, and gravitational perturbations of an Ay\'on-Beato-Garc\'ia black hole surrounded by quintessence using the Asymptotic Iteration Method (30 iterations). The results are compared with the WKB approximation to evaluate the robustness and accuracy of AIM. The results show that the real part of the frequencies increases with the charge parameter, while the absolute value of the imaginary part decreases as the charge parameter increases. In contrast, both the real part and the absolute value of the imaginary part decrease as the quintessence parameter $c$ increases. These trends are observed for both values of the quintessence state parameter, $\omega_q=-2/3$ and $\omega_q=-4/9$; however, the effects become more pronounced as $\omega_q$ approaches $-1$ corresponding to cosmological constant. The quasi-normal frequencies tend to have finite values, which could facilitate their observational detection. Moreover, the presence of quintessence leads to a slower damping of the perturbations.

gr-qc↗

arXiv2025

Spectral analysis of Dirac materials in position-dependent magnetic and electric fields via Heun functions

This work focuses on the study of the spectral problem for Dirac materials immersed in position-dependent magnetic and electric fields. To achieve this, the system of differential equations satisfied by the eigenfunction components of the Hamiltonian has been decoupled, and the solutions for some specific cases have been analyzed using Heun functions, which provide us with a quantization relation and allow us to determine the solutions for the bound states.

math-ph↗

arXiv2025

Quasi-normal modes and absorption section from regular black holes immersed in perfect fluid dark matter

We study scalar, electromagnetic and gravitational perturbations of three families of regular black holes, Hayward, Bardeen, and Ayon-Beato-Garc\'ia immersed in a Perfect Fluid Dark Matter (PFDM) background. Using both the sixth-order WKB approximation and the Asymptotic Iteration Method (AIM), we determine the corresponding quasi-normal modes and absorption cross sections. By fixing the horizon radius, we analyze the dependence of the parameters of the black holes and the parameter of PFDM. The computed quasi-normal modes confirm the dynamical stability of the black holes under scalar, electromagnetic and gravitational perturbations. Furthermore, both the real and imaginary parts of the quasi-normal modes increase with the multipole number $l$, corresponding to higher oscillation frequencies and faster damping rates. On the other hand, absorption cross sections are compared under similar parametric conditions. The results demonstrate that PFDM influences the dynamical properties of regular black holes.

gr-qc↗

arXiv2024

Quasinormal modes of the Schwarzschild black hole with a deficit solid angle and quintessence-like matter: Improved asymptotic iteration method

We study the quasinormal modes (QNM) for scalar, and electromagnetic perturbations in the Schwarzschild black hole with a deficit solid angle and quintessence-like matter. Using the sixth--order WKB approximation and the improved asymptotic iteration method (AIM) we can determine the dependence of the quasinormal modes on the parameters of the black hole and the parameters on the test fields. The values of the real part and imaginary parts of the quasi--normal modes increase with the decrease of the values of the deficit solid angle and density of quintessence-like matter. The quasinormal modes gotten by these two methods are in good agreement. Using the finite difference method, we obtain the time evolution profile of such perturbations in this Black Hole.

gr-qc↗

arXiv2022

Effects of quintessence on scattering and absorption sections of black holes

Basing on the ideas used by Kiselev, we study three black holes surrounded by quintessence and the effects of quintessence on the classical and semiclassical scattering cross-sections. In contrast, the absorption section is studied with the sinc approximation in the eikonal limit. For Schwarzschild, Reissner-Nordström and Bardeen black holes surrounded by quintessence, the values critical of charges and the normalization factor are obtained. We also described the horizons and the extremal condition of the black holes surrounded by quintessence. By setting for the quintessence state parameter in two the particular cases w=-2/3 and w=-1/2.

gr-qc↗

arXiv2021

Quasinormal modes of the Hayward black hole surrounded by quintessence: scalar, electromagnetic and gravitational perturbations

We study the quasi-normal modes for scalar, electromagnetic, and gravitational axial perturbations in the Hayward regular black hole surrounded by quintessence (HBH-$ω_q$). Using the third--order WKB approximation we can determine the dependence of the quasi--normal modes on the parameters of the regular black hole and the parameters on the test fields. We also determine the greybody factor, giving transmission and reflection coefficients of the scattered wave through the effective potentials in the WKB approximation using numerical analysis.

gr-qc↗

arXiv2021

Scattering and absorption sections of Schwarzschild-anti de Sitter with quintessence

In this paper, we study the scattering and absorption sections of the Schwarzschild--anti de Sitter black hole surrounded by quintessence. The critical values of the cosmological constant and the normalization factor are obtained. We describe the event horizons and the extremal condition of the black hole surrounded by quintessence. The effects of quintessence on the classical and semi--classical scattering cross--sections have been estimated. Also, the absorption section is studied with the sinc approximation in the eikonal limit. We consider the quintessence state parameter in the particular cases $ω=-2/3$ and $ω=-1/2$.

gr-qc↗

arXiv2020

Geodesics of Hayward black hole surrounded by quintessence

Basing on the ideas used by Kiselev, we study the Hayward black hole surrounded by quintessence. By setting for the quintessence state parameter at the special case of $ω=-\frac{2}{3}$, using the metric of the black hole surrounded by quintessence and the definition of the effective potential, we analyzed in detail the null geodesics for different energies. We also analyzed the horizons of the Hayward black hole surrounded by quintessence as well as the shadow of the black hole.

gr-qc↗

arXiv2017

Corotating two-body system of identical Kerr sources

A binary system of identical corotating Kerr sources is studied after deriving the corresponding 3-parametric asymptotically flat exact solution. Both sources are apart from each other by means of a massless strut (conical singularity). In the context of black holes, the analytical functional form of each horizon σ is expressed in terms of arbitrary Komar physical parameters: mass M, angular momentum J (with parallel spin), and the coordinate distance R between the center of each horizon. Later on, all the thermodynamical properties related to the horizon are depicted by concise formulae. Finally, the extreme limit case is obtained as a 2-parametric subclass of Kinnersley-Chitre metric.

gr-qc↗

arXiv2013

Gravitational potential of a point mass in a brane world

In brane world models, combining the extra dimensional field modes with the standard four dimensional ones yields interesting physical consequences that have been proved from high energy physics to cosmology. Even some low energy phenomena have been considered along these lines to set bounds on the brane model parameters. In this work we extend to the gravitational realm a previous result which gave finite electromagnetic and scalar potentials and self energies for a source looking pointlike to an observer sitting in a 4D Minkowski subspace of the single brane of a Randall-Sundrum spacetime including compact dimensions. We calculate here the gravitational field for the same type of source by solving the linearized Einstein equations. Remarkably, it turns out to be also non singular. Moreover, we use gravitational experimental results of the Cavendish type and the Parameterized Post Newtonian (PPN) coefficients, to look for admissible values of the brane model parameters. The anti de Sitter radius hereby obtained is concordant with previous results based on Lamb shift in hydrogen. However, the resulting PPN parameters lie outside the acceptable value domain.

hep-ph↗

arXiv2011

Brane world regularization of point particle classical self-energy

Physical effects in brane worlds models emerge by the incorporation of field modes coming from extra dimensions with the usual four dimensional ones. Such effects can be tested with well established experiments to set bounds on the parameters of the brane models. In this work we extend a previous result which gave finite electromagnetic potentials and self energies for a source looking pointlike to an observer sitting in a 4D Minkowski subspace of a single brane of a Randall-Sundrum spacetime including compact dimensions, and along which the source stretches uniformly. We show that a scalar particle produces a nonsingular static potential, possess a finite self-energy and that technically its analysis is very similar to the electrostatic case. As for the latter, we use the deviations from the Coulomb potential to set bounds on the anti de Sitter radius of the brane model on the basis of two experiments, namely, one of the Cavendish type and other being the scattering of electrons by Helium atoms. We found these are less stringent than others previously obtained using the Lamb shift in Hydrogen.

hep-ph↗

arXiv2010

Casimir force in brane worlds: coinciding results from Green's and Zeta function approaches

Casimir force encodes the structure of the field modes as vacuum fluctuations and so it is sensitive to the extra dimensions of brane worlds. Now, in flat spacetimes of arbitrary dimension the two standard approaches to the Casimir force, Green's function and zeta function, yield the same result, but for brane world models this was only assumed. In this work we show both approaches yield the same Casimir force in the case of Universal Extra Dimensions and Randall-Sundrum scenarios with one and two branes added by p compact dimensions. Essentially, the details of the mode eigenfunctions that enter the Casimir force in the Green's function approach get removed due to their orthogonality relations with a measure involving the right hyper-volume of the plates and this leaves just the contribution coming from the Zeta function approach. The present analysis corrects previous results showing a difference between the two approaches for the single brane Randall-Sundrum; this was due to an erroneous hyper-volume of the plates introduced by the authors when using the Green's function. For all the models we discuss here, the resulting Casimir force can be neatly expressed in terms of two four dimensional Casimir force contributions: one for the massless mode and the other for a tower of massive modes associated with the extra dimensions.

hep-th↗

arXiv2008

Brane world corrections to scalar vacuum force in RSII-p

Vacuum force is an interesting low energy test for brane worlds due to its dependence on field's modes and its role in submillimeter gravity experiments. In this work we generalize a previous model example: the scalar field vacuum force between two parallel plates lying in the brane of a Randall-Sundrum scenario extended by $p$ compact dimensions (RSII-$p$). Upon use of Green's function technique, for the massless scalar field, the 4D force is obtained from a zero mode while corrections turn out attractive and depend on the separation between plates as $l^{-(6+p)}$. For the massive scalar field a quasilocalized mode yields the 4D force with attractive corrections behaving like $l^{-(10+p)}$. Corrections are negligible w.r.t. 4D force for $AdS_{(5+p)}$ radius less than $\sim 10^{-6}$m. Although the $p=0$ case is not physically viable due to the different behavior in regard to localization for the massless scalar and electromagnetic fields it yields an useful comparison between the dimensional regularization and Green's function techniques as we describe in the discussion.

hep-ph↗

arXiv2007

Casimir force for a scalar field in warped brane worlds

In looking for imprints of extra dimensions in brane world models one usually builts these so that they are compatible with known low energy physics and thus focuses on high energy effects. Nevertheless, just as submillimeter Newton's law tests probe the mode structure of gravity other low energy tests might apply to matter. As a model example, in this work we determine the 4D Casimir force corresponding to a scalar field subject to Dirichlet boundary conditions on two parallel planes lying within the single brane of a Randall-Sundrum scenario extended by one compact extra dimension. Using the Green's function method such a force picks the contribution of each field mode as if it acted individually but with a weight given by the square of the mode wave functions on the brane. In the low energy regime one regains the standard 4D Casimir force that is associated to a zero mode in the massless case or to a quasilocalized or resonant mode in the massive one whilst the effect of the extra dimensions gets encoded as an additional term.

hep-ph↗

arXiv2006

Low-energy effects in brane worlds: Liennard-Wiechert potentials and Hydrogen Lamb shift

Testing extra dimensions at low-energies may lead to interesting effects. In this work a test point charge is taken to move uniformly in the 3-dimensional subspace of a (3+$n$)-brane embedded in a (3+$n$+1)-space with $n$ compact and one warped infinite spatial extra dimensions. We found that the electromagnetic potentials of the point charge match standard Liennard-Wiechert's at large distances but differ from them close to it. These are finite at the position of the charge and produce finite self-energies. We also studied a localized Hydrogen atom and take the deviation from the standard Coulomb potential as a perturbation. This produces a Lamb shift that is compared with known experimental data to set bounds for the parameter of the model. This work provides details and extends results reported in a previous Letter.

physics.atom-ph↗

arXiv2006

Casimir effect in a six-dimensional vortex scenario

Recently Randjbar-Daemi and Shaposhnikov put forward a 4-dimensional effective QED coming from a Nielsen-Olesen vortex solution of the abelian Higgs model with fermions coupled to gravity in D=6. However, exploring possible physical consequences of such an effective QED was left open. In this letter we study the corresponding effective Casimir effect. We find that the extra dimensions yield fifth and third inverse powers in the separation between plates for the modified Casimir force which are in conflict with known experiments, thus reducing the phenomenological viability of the model.

hep-ph↗