arXiv subjects

A. El Balali

Publications and source records attributed to A. El Balali.

7 recordsLinked to original sources

arXiv2024

Cosmological Constant Effect on Charged and Rotating Black Hole Shadows

Motivated by recent astrophysical observations, we investigate the shadow behaviors of four dimensional charged rotating black holes with a cosmological constant. This study is made in terms of a reduced moduli space parameterized by the charge and the rotation parameters. For fixed observers, we analyse in some details the shadow behaviors and the corresponding naked singularities of Kerr-Newman and Kerr-Sen four-dimensional black holes in Anti de Sitter backgrounds. Then, a comparative discussion is provided by computing the geometrical observables and the energy emission rate.

gr-qc↗

arXiv2024

Deflection angle and shadow of slowly rotating black holes in galactic nuclei

In this paper, we construct the slowly rotating case of an asymptotically flat supermassive black hole embedded in dark matter using Newman-Janis procedure. Our analysis is carried with respect to the involved parameters including the halo total mass $M$ and the galaxy's lengthscale $a_0$. Concretly, we investigate the dark matter impact on the effective potential and the photon sphere. In particular, we find that the lengthscale $a_0$ controles such potential values. Indeed, for low $a_0$ values, we find that the halo total mass $M$ decreases the potential values significantly while for high $a_0$ values such impact is diluted. Regarding the shadow aspects, we show that the shadow size is much smaller for high values of $a_0$ while the opposite effect is observed when the halo total mass $M$ is increased. By comparing our case to the slowly rotating case, we notice that the former exhibits a shadow shifted from its center to the left side. Finally, we compute the deflection angle in the weak-limit approximation and inspect the dark matter parameters influence. By ploting such quantity, we observe that one should expect lower bending angle values for black holes in galactic nuclei.

gr-qc↗

arXiv2021

Black Hole Shadows in M-theory Scenarios

We study the shadows of four dimensional black holes in M-theory inspired models. We first inspect the influence of M2-branes on such optical aspects for non-rotating solutions. In particular, we show that the M2-brane number can control the circular shadow size. This geometrical behavior is distorted for rotating solutions exhibiting cardioid shapes in certain moduli space regions. Implementing a rotation parameter, we analyze the geometrical shadow deformations. Among others, we recover the circular behaviors for a large M2-brane number. Investigating the energy emission rate at high energies, we find, in a well-defined approximation, that the associated peak decreases with the M2-brane number. Moreover, we investigate a possible connection with observations (from Event Horizon Telescope or future devices) from a particular M-theory compactification by deriving certain constraints on the M2-brane number in the light of the $M87^\star$ observational parameters.

hep-th↗

arXiv2020

Deflection Angle and Shadow Behaviors of Quintessential Black Holes in arbitrary Dimensions

Motivated by M-theory/superstring inspired models, we investigate certain behaviors of the deflection angle and the shadow geometrical shapes of higher dimensional quintessential black holes associated with two values of the dark energy (DE) state parameter, being ω=-\frac{1}{3} and ω=-\frac{2}{3}. Concretely, we derive the geodesic equation of photons on such backgrounds. Thanks to the Gauss-Bonnet theorem corresponding to the optical metric, we compute the leading terms of the deflection angle in the so-called weak-limit approximation. After that, we inspect the effect of DE and the space-time dimension d on the calculated optical quantities. Introducing DE via the field intensity c and the state parameter ω, we find that the shadow size and the deflection angle increase by increasing values of the field intensity c. However, we observe that the high dimensions decrease such quantities for ω-models exhibiting similar behaviors. Then, we consider the effect of the black hole charge, on these optical quantities, by discussing the associated behaviors. The present investigation recovers certain known results appearing in ordinary four dimensional models.

gr-qc↗

arXiv2020

On Phase Transition Behaviors of Kerr-Sen Black Hole

We investigate phase transitions and critical behaviors of the Kerr-Sen black hole in four dimensions. Computing the involved thermodynamical quantities including the specific heat and using the Ehrenfest scheme, we show that such a black hole undergoes a second-order phase transition. Adopting a new metric form derived from the Gibss free energy scaled by a conformal factor associated with extremal solutions, we calculate the geothermodynamical scalar curvature recovering similar phase transitions. Then, we obtain the scaling laws and the critical exponents, matching perfectly with mean field theory.

hep-th↗

arXiv2020

Phase Transitions of Quintessential AdS Black Holes in M-theory/Superstring Inspired Models

We study $d$-dimensional $AdS$ black holes surrounded by Dark Energy (DE), embedded in $D$-dimensional M-theory/superstring inspired models having $AdS_d \times \mathbb{S}^{d+k}$ space-time with $D=2d+k$. We focus on the thermodynamic Hawking-Page phase transitions of quintessential DE black hole solutions, whose microscopical origin is linked to $N$ coincident $(d-2)$-branes supposed to live in such $(2d+k)$-dimensional models. Interpreting the cosmological constant as the number of colors $\propto N^{\frac{d-1}{2}}$, we calculate various thermodynamical quantities in terms of brane number, entropy and DE contributions. Computing the chemical potential conjugated to the number of colors in the absence of DE, we show that a generic black hole is more stable for a larger number of branes for lower dimensions $d$.In the presence of DE, we find that the DE state parameter $ω_q$ should take particular values, for $(D,d,k)$ models, providing a non trivial phase transition structure.

hep-th↗

arXiv2019

Dark Energy Effects on Charged and Rotating Black Holes

Using canonical typicality method, we reconsider the study of dark energy effects on four dimensional black holes. Concretely, we investigate the associated influences on the spectrum of various black hole backgrounds including the charged and the rotating ones. For such black hole solutions, we first elaborate analytically the corresponding radiation spectrum, the Hawking temperature and the dark information. Then, we discuss and analyze the corresponding findings. This work, recovering the results of the Schwarzschield black hole, confirms that dark energy can be considered as a cooling system surrounding the black holes providing a colder radiation and a slower Hawking radiation process.

hep-th↗