arXiv subjects

M. Benali

Publications and source records attributed to M. Benali.

At least 19 recordsLinked to original sources

arXiv2024

Rotating reduced Kiselev black holes: Shadows, Energy emission and Deflection of light

In this paper, we generate a rotating solution of the reduced Kiselev black hole through the Newman-Janis formalism. Based on such solution, we remark different shadow behaviors by varying the involved parameters $r_k, a, \alpha$. Concretely, we observe that the allowed values of the spin parameter $a$ are much less than the usual rotating black holes. By deeply analysing the shadow shapes, we show that comparable shadow shapes emerge for the same ratio $a/r_k$. On the other hand, we recognize that the parameters $a$ and $\alpha$ governs the shadow geometry while the parameter $r_k$ rules the size of such a quantity. Besides, we notice that an elliptic shadow geometry appears for certain range of relevant parameters. By making contact with the observational side, we provide a constraint on the rotating reduced Kiselev (RRK) black hole parameters. In particular, we find a good compatibility between the theoretical and experimental results. Regarding Hawking radiation, we note that the Kiselev radius $r_ k$ shows a similar behavior to the quintessence filed intensity $\mathbf{c}$. Concerning the light motion in the vicinity of a RRK black hole, we investigate deeply the deflection by varying the relevant parameters. In particular, we remark that such a quantity decreases by increasing the parameters $a$ and $\alpha$ while the opposite effect is observed when increasing $r_k$.

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↗

arXiv2023

Deflection angle and Shadows by Black Holes in Starobinsky-Bel-Robinson Gravity from M-theory

Motivated by M-theory compactifications, we investigate optical properties of black holes in the Starobinsky-Bel-Robinsion gravity. Precisely, we study the shadows and the deflection angle of light rays by non-rotating and rotating black holes in such a novel gravity. We start by discussing the shadows of the Schwarzschild-type solutions. As expected, we obtain perfect circular shadows where the size decreases with a stringy gravity parameter denoted by $\beta$. We show that this parameter is constrained by the shadow existence. Combining the Newman-Janis algorithm and the Hamilton-Jacobi mechanism, we examine the shadow behaviors of the rotating solutions in terms of one-dimensional real curves. Essentially, we find various sizes and shapes depending on the rotating parameter and the stringy gravity parameter $a$ and $\beta$, respectively. To inspect the shadow geometric deformations, we investigate the astronomical observables and the energy emission rate. As envisaged, we reveal that $a$ and $\beta$ have an impact on such shadow behaviors. For specific values of $a$, we remark that the obtained shadow shapes share certain similarities with the ones of the Kerr black holes in plasma backgrounds. Using the Event Horizon Telescope observational data, we provide predictions for the stringy gravity parameter $\beta$ which could play a relevant role in M-theory compactifications. We finish this work by a discussion on the behaviors of the light rays near to such four dimensional black holes by computing the deflection angle in terms of a required moduli space.

hep-th↗

arXiv2023

On Inflationary Models in f(R,T) Gravity with a Kinetic Coupling Term

We investigate inflationary models in f(R,T) modified gravity with a kinetic coupling term \omega^2 G^{\mu\nu}\partial_{\mu}\phi\partial_{\nu}\phi having a positive factor needed to remove the ghosts. Taking f(R,T)=R+2\beta T, we calculate and analyse the relevant observable quantities including the spectral index $n_s$ and the tensor-to-scalar ratio r using the slow-roll approximations. Concretely, we consider two scenarios described by the decoupling and the coupling behaviors between the scalar potential and the f(R,T) gravity via the moduli space by dealing with two potentials being the quartic one V(\phi) =\lambda \phi^4 and the small field inflation V(\phi) =V_0(1- (\frac{\phi}{\mu})^\alpha). For the quartic inflation model, we consider a decoupling behavior. For the small field inflation, however, we present the parameter decoupling and coupling scenarios. For both scenarios, we compute and inspect n_s and r showing interesting results. For three different values of the number of e-folds N=60,65 and 70, we find that the coupling between f(R,T)1 and the scalar potential via the moduli space provides an excellent agreement with the observational findings. In the last part of this work, we provide a possible discussion on the amplitude of scalar power spectrum needed to provide a viability of the proposed theory. Considering the second potential form in the parameter coupling scenario, we find acceptable values in certain points of the moduli space.

hep-th↗

arXiv2023

Light Behaviors around Black Holes in M-theory

We study the deflection angle and the trajectory of the light rays around black holes in M-theory scenarios. Using the Gauss-Bonnet theorem, we first compute and examine the deflection angle of the light rays near four and seven-dimensional AdS black holes obtained from the M-theory compactifications on the real spheres on $S^7$ and $S^4$, respectively. We discuss the effect of the M-theory brane number and the rotating parameter on such an optical quantity. We then investigate the trajectories of the light rays using the equation of motion associated with $M2$ and $M5$ branes.

hep-th↗

arXiv2022

Light Trajectories and Thermal Shadows casted by Black Holes in a Cavity

We explore the shadows and the photon rings casted by black holes in cavity. Placing the observer inside such an isothermal background, we examine the influence of the cavity temperature T_{cav} and the charge Q on the involved optical aspect. After studying the effect of the horizon radius by varying Q, we investigate the thermal behaviors of the black hole shadows in a cavity. For fixed charge values, we find that the shadow radius r_s increases by decreasing T_{cav}. Varying such a temperture, we discuss the associated energy emission rate. After that, we show that the curves in the r_s-T_{cav} plane share similarities with the G-T curves of the Anti de Sitter (AdS) black holes. Then, we study the trajectory of the light rays casted by black holes in a cavity. We further observe that the light trajectory behaviors are different than the ones of the non rotating black holes due to the cavity effect. Finally, we provide evidence for the existence of an universal ratio defined in terms of the photon sphere radius and the impact parameter. Concretely, we obtain a optical ratio \frac{b_{sp}}{r_{sp}} \sim \sqrt 3.

gr-qc↗

arXiv2022

Light Deflection by Rotating Regular Black Holes with a Cosmological Constant

Using the Gauss-Bonnet theorem, we compute and examine the deflection angle of light rays by rotating regular black holes with a cosmological constant. By the help of optical geometries, we first deal with the Hayward black holes with cosmological contributions. Then, we reconsider the study of the Bardeen solutions. We inspect the cosmological constant effect on the deflection angle of light rays. Concretely, we find extra cosmological correction terms generalizing certain obtained findings. Using graphical analysis, we provide a comparative discussion with respect to the Kerr solutions. The results confirm that the non-linear electrodynamic charges affect the space-time geometry by decreasing the deflection angle of light rays by such cosmological black holes.

gr-qc↗

arXiv2022

Light Deflection Angle by Superentropic Black Holes

Motivated by recent works on light deflection and shadow behaviors on AdS geometries, we investigate the deflection angle of light rays by superentropic black holes. Taking appropriate approximations, we first obtain the involved expression. For large values of the impact parameter, we get a specific value being zero for ordinary black holes without AdS backgrounds. Then, we examine and analyze such an optical quantity by providing graphical discussions in terms of a bounded region of the moduli space required by superentropic black hole conditions. Concretely, we study the deflection angle aspects by varying the black hole mass being fixed in the previous findings.

gr-qc↗

arXiv2022

Superentropic Black Hole Shadows in Arbitrary Dimensions

We investigate the shadow behaviors of the superentropic black holes in arbitrary dimensions. Using the Hamilton-Jacobi mechanism, we first obtain the associated null geodesic equations of motion. By help of a spheric stereographic projection, we discuss the shadows in terms of one-dimensional real curves. Fixing the mass parameter m, we obtain certain shapes being remarkably different than four dimensional geometric configurations. We then study theirs behaviors by varying the black hole mass parameter. We show that the shadows undergo certain geometric transitions depending on the spacetime dimension. In terms of a critical value mc, we find that the four dimensional shadows exhibit three configurations being the D-shape, the cardioid and the naked singularity associated with m > mc, m = mc and m < mc, respectively. We reveal that the D-shape passes to the naked singularity via a critical curve called cardioid. In higher dimensions, however, we show that such transitional behaviors are removed.

hep-th↗

arXiv2022

Thermodynamic and Optical Behaviors of Quintessential Hayward-AdS Black Holes

Motivated by Dark Energy (DE) activities, we study certain physical behaviors of the quintessential Hayward-AdS black holes in four dimensions. We generalize some physical properties of the ordinary Hayward AdS black holes without the dark sector. We elaborate a study in terms of the new quantities $c$ and $\omega_q$ parametrizing the dark sector moduli space. We investigate the effect of such parameters on certain thermodynamic and optical aspects. To show the quintessential thermodynamic behaviors, we first reconsider the critical properties of ordinary solutions. We find that the equation of state predicts a universal ratio given by $\chi_0=\frac{P_cv_c}{T_c}=\frac{27-3\sqrt{6}}{50}$, which is different than the universal one appearing for Van der Waals fluids. Considering the quintessential solutions and taking certain values of the DE state parameter $\omega_q$, we observe that the new ratio depends on the DE scalar field intensity $c$. In certain regions of the moduli space, we show that this ratio can be factorized using two terms describing the absence and the presence of the dark sector. Then, we analyze also the DE effect on the heat engines. For the optical aspect, we study the influence of DE on the shadows using one-dimensional real curves. Finally, we discuss the associated energy emission rate, using the dark sector.

hep-th↗

arXiv2021

Deflection Light Behaviors by AdS Black Holes

We investigate the behavior of the deflection of light rays by charged and rotating AdS black holes using the Gauss-Bonnet formalism. Taking weak field approximations and certain appropriate limits associated with AdS geometries, we compute and analyze such an optical quantity by varying the involved moduli space parameters. First, we study the charge and the AdS radius effects on the deflection angle of RN-AdS black holes. For small values of the impact parameter $b$, we find that the charge effect is relevant. Precisely, it decreases the deflection angle, while the AdS background one is not. For large values of $b$, however, these optical behaviors have been inverted and the deflection angle becomes an increasing function of the charge. In this way, the cosmological constant effect is remarked to be relevant showing linear variations of the deflection angle. Varying the charge, we find a critical impact parameter value $b_{c}$ where the charge effect is inverted. For rotating solutions, we show that the spinning parameter still decreases the deflection angle without any changing behavior observed in the charge effect. Evincing of the cosmological constant, we recover known results corresponding to charged and rotating ordinary black hole solutions. Examining the plasma effect, we reveal that the deflection angle keeps the same behavior being a decreasing function in terms of the frequency ratio.

hep-th↗

arXiv2021

Superentropic AdS Black Hole Shadows

We study shadow aspects of superentropic black holes in four dimensions. Using Hamilton-Jacobi formalism, we first get the null geodesic equations. In the celestial coordinate framework relying on fixed positions of observers, we investigate the shadow behaviors in terms of the mass and the cosmological scale variation parameters. Among others, we obtain ellipse shaped geometries contrary to usual black hole solutions. Modifying the ordinary relations describing geometrical observables, we discuss the size and the shape deformation parameters of these non-trivial geometric forms. Due to horizonless limits associated with certain mass values, we explore the shadow of the naked singularity of such black holes.

hep-th↗

arXiv2021

Deeply virtual Compton scattering off the neutron

The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly-energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark's transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasi-free neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton's internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle.

hep-ph↗

arXiv2021

On M-theory on Real Toric Fibrations

Borrowing ideas from elliptic complex geometry, we approach M-theory compactifications on real toric fibrations. Precisely, we explore real toric equations rather than complex ones exploited in F-theory and related dual models. These geometries have been built by moving real circles over real bases. Using topological changing behaviors, we unveil certain data associated with gauge sectors relying on affine Lie symmetries.

hep-th↗

arXiv2021

Measurement of the Generalized Polarizabilities of the Proton at Intermediate $Q^2$

Background: Generalized polarizabilities (GPs) are important observables to describe the nucleon structure, and measurements of these observables are still scarce. Purpose: This paper presents details of a virtual Compton scattering (VCS) experiment, performed at the A1 setup at the Mainz Microtron by studying the $e p \to e p γ$ reaction. The article focuses on selected aspects of the analysis. Method: The experiment extracted the $P_{LL} -P_{TT} / ε$ and $P_{LT}$ structure functions, as well as the electric and magnetic GPs of the proton, at three new values of the four-momentum transfer squared $Q^2$: 0.10, 0.20 and 0.45 GeV$^2$. Results: We emphasize the importance of the calibration of experimental parameters. The behavior of the measured $e p \to e p γ$ cross section is presented and compared to the theory. A detailed investigation of the polarizability fits reveals part of their complexity, in connection with the higher-order terms of the low-energy expansion. Conclusions: The presented aspects are elements which contribute to minimize the systematic uncertainties and improve the precision of the physics results.

nucl-ex↗

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

Shadows of 5D Black Holes from String Theory

We study the shadow behaviors of five dimensional (5D) black holes embedded in type IIB superstring/supergravity inspired spacetimes by considering solutions with and without rotations. Geometrical properties as shapes and sizes are analyzed in terms of the D3-brane number and the rotation parameter. Concretely, we find that the shapes are indeed significantly distorted by such physical parameters and the size of the shadows decreases with the brane or "color" number and the rotation. Then, we investigate geometrical observables and energy emission rate aspects.

hep-th↗