arXiv subjects

A. Belhaj

Publications and source records attributed to A. Belhaj.

At least 19 recordsLinked to original sources

arXiv2026

Reconstructing slow-roll Scalar-Tensor Gauss-Bonnet single field inflation from running spectral data

We examine cosmological inflation in a broad family of scalar-tensor models characterized by scalar-dependent non minimal kinetic couplings and Gauss-Bonnet terms. Using a slow roll-approximation, we compute in detail theoretical expectations of observables as spectral indexes, scalar-to-tensor ratio, their running and their running of the running in terms of the parameters which characterize the scalar-tensor model. Hierarchies of consistency equations relating scalar and tensor pertubations and higher order running parameters are presented and examined at the slow roll approximation for the kind of models of interest in this work. From We find detailed expressions for constraints among these parameters. For a specific model, we analyse such quantities and make contact with latest Planck observational data .

hep-th↗

arXiv2026

On Computational CUDA Studies of Black Hole Shadows

Combining high-performance CUDA numerical codes with the Hamilton--Jacobi formalism, we investigate the shadows properties of rotating charged Euler--Heisenberg black holes in the presence of global monopoles. Then, we discuss the associated energy emission rate by varying the involved black hole parameters. As a result, we show that both the shadow structure and the energy emission rate depend on the global monopole parameter, the electric charge, and the rotation parameter. However, we observe that the Euler--Heisenberg nonlinear parameter does not significantly affect either the shadow or the energy emission rate. In order to reconcile the present theoretical predictions with the shadow observations reported by the Event Horizon Telescope collaboration, we employ a CUDA-based computational approach to establish strict bounds on the GM parameter, the electric charge, and the rotation parameter.

physics.gen-ph↗

arXiv2025

Black Holes and Black Strings in M-theory on Calabi-Yau threefolds with four Kähler parameters

Combining toric geometry techniques and $\mathcal{N}=2$ supergravity formalisms, we study 5D black branes in the M-theory compactification on a four parameter Calabi-Yau threefold. First, we investigate 5D BPS and non-BPS black holes that are derived by wrapping M2-branes on non-holomorphic 2-cycles in such a toric Calabi-Yau manifold. Concretely, we provide the allowed electric charge regions of BPS and non-BPS black hole states that are obtained by surrounding M2-branes over appropriate 2-cycles. Then, we approach the black hole thermodynamic behavior by computing the entropy and the temperature. By evaluating the recombination factor, we examine the stability of such non-BPS black holes. Precisely, we find stable and unstable solutions depending on the allowed electric charge regions. After that, we study 5D black strings by wrapping M5-branes on non-holomorphic dual 4-cycles in the proposed toric Calabi-Yau manifold by focusing on the stability behaviors. In the allowed regions of the moduli space of the non-BPS stringy solutions, we find stable and unstable states depending on the magnetic charge values.

hep-th↗

arXiv2024

On M87$^$ and SgrA$^$ Observational Constraints of Dunkl Black Holes

In this work, we investigate the optical properties of a new black hole recently obtained from the Dunkl operator formalism involving a relevant parameter denoted by $ξ$. Concretely, we first investigate the shadows, the Lyapunov exponents of unstable nearly bound orbits and the spherically infalling accretion behaviors in terms of such a parameter. Then, we examine the effect of this parameter on the Dunkl black hole deflection angle in vacuum and medium backgrounds by manipulating the Gauss-Bonnet theorem. Exploiting the M87$^*$ and SgrA$^*$ optical bonds, we provide strong constraints on $ξ$ via the falsification mechanism.

gr-qc↗

arXiv2024

On Gravity Implication in the Wavefunction Collapse

Inspired by an ontic view of the wavefunction in quantum mechanics and motivated by the universal interaction of gravity, we discuss a possible gravity implication in the state collapse mechanism. Concretely, we investigate the stability of the spatial superposition of a massive quantum state under the gravity effect. In this context, we argue that the stability of the spatially superposed state depends on its gravitational self-energy originating from the effective mass density distribution through the spatially localized eigenstates. We reveal that the gravitational self-interaction between the different spacetime curvatures created by the eigenstate effective masses leads to the reduction of the superposed state to one of the possible localized states. Among others, we discuss such a gravity-driven state reduction. Then, we approach the corresponding collapse time and the induced effective electric current in the case of a charged state, as well as the possible detection aspects.

hep-th↗

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

On Exchange-Correlation Energy in DFT Scenarios

Motivated by the considerable importance of material properties in modern condensed matter physics research, and using techniques of the $N_{e}$ -electron systems in terms of the electron density $n_{σe}\left( r\right) $ needed to obtain the ground-state energy $E_{e}$ in Density Functional Theory scenarios, we approach the Exchange-Correlation energy $ E_{xc}\left[ n_{σe}(r)\right] $ by considering the interelectronic position corrections $Δr_{x}^{\uparrow \uparrow ,\uparrow \downarrow }=λ_{x}\left\vert δr^{\uparrow \uparrow }-δr^{\uparrow \downarrow }\right\vert $ and $Δr_{c}^{e_{i}e_{j\neq i}}=λ_{c}\left\vert r-r^{\prime }\right\vert ^{-\left( N_{e}-1\right) ^{-1}}$ corresponding to the spin and the Coulomb correlation effects, respectively, through the electron-electron potential energy. Exploiting such corrections, we get approximate expressions for the exchange $E_{x}\left[ n_{σe} \right] $ and the correlation $E_{c}\left[ n_{σe}\right] $ functional energies which could be interpreted in terms of magnetic and electric dipole potential energies associated with the charge density $n_{σe}\left( r\right) $ described by inverse-square potential behaviors. Based on these arguments, we expect that such obtained Exchange-Correlation functional energy could be considered in the Local Density Approximation functional as an extension to frame such interelectronic effects.

cond-mat.mtrl-sci↗

arXiv2024

On 5D Black Brane Stabilities from M-theory on Three Parameter Calabi-Yau Threefolds

In this work, we reconsider the study of 5D black branes in M-theory compactifications by means of $\mathcal{N}=2$ supergravity formalism. Precisely, we provide a model relaying on a three parameter Calabi-Yau manifold in the $\mathbb{P}^{1}\times\mathbb{P}^{1}\times\mathbb{P}^{2}$ projective space factorization, referred to as economical model. First, we investigate the stability of 5D BPS and non-BPS black holes obtained from wrapped M2-branes on non-holomorphic two-cycles in such a Calabi-Yau manifold. Then, we approach the stability of 5D black strings derived from wrapped M5-branes on non-holomorphic four-cycles. Among others, we find various stable and unstable black brane solutions depending on the charge regions of the involved moduli space.

hep-th↗

arXiv2024

On Inflation and Axionic Dark Matter in a Scaled Gravity

Motivated by the modified gravity theories $F(R)\neq R$ and inflationary physics, we first propose and investigate an inflation model in a scaled gravity $F(R)=R\,+βR$, where $β$ is a dimensionless scaling parameter. The latter is also implemented in a particular potential $V(ϕ)=M^{4}\left[ 1-\cos \left( \frac{ϕ}μ\right)^{β}\right] $ being considered to drive the inflation via a parameter coupling scenario. Using the slow-roll approximations, the gravity scale parameter $β$ is approached with respect to the range of the associated computed cosmological observables $n_{s}$ and $r$ according to the recent Planck and BICEP/Keck data. Then, we discuss the axionic dark matter in the suggested gravity model by considering the case where the inflaton is taken to be identified with an axion-like field $ϕ=f_{a}θ$ with the decay constant $f_{a}=μ$. Referring to the known data, the underlying inflation scale $M$ is constrained to be much lower than the corresponding axion scale $M\ll f_{a}$.

hep-th↗

arXiv2024

Probing Quantum Entanglement from Quantum Correction to Newtonian Potential Energy

Inspired by string theory ideas, we probe quantum entanglement from the gravitational potential energy. Concretely, we reconsider the study of quantum corrections to the Newtonian potential energy by treating a massive two-particle system $m_{1}$ and $m_{2}$ with size dimensions $r_{1}$ ad $% r_{2}$ where the two particles separated by a distance $d$ are under only their mutual classical gravitational interaction $V_{r}\left( r_{1}\text{, }% r_{2}\right) $. Exploring such a size-dependent gravitational behavior and taking the limit $r_{1}$, $r_{2}\ll d$, we investigate the associated quantum biparticle state and express its evolution after an interaction time $τ$. Among others, we show that the two masses cannot be separable due to the induced gravitational entanglement in terms of the accumulated quantum phase $δϕ=δV_{g}τ/\hbar $. By analogy with the classical gravity, we derive the expression of the resulting extremely weak entanglement force from the corresponding gravitational entanglement energy. Then, we provide certain entanglement diagnostics.

quant-ph↗

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 $β$. 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 $β$, respectively. To inspect the shadow geometric deformations, we investigate the astronomical observables and the energy emission rate. As envisaged, we reveal that $a$ and $β$ 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 $β$ 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 ω^2 G^{μν}\partial_μϕ\partial_νϕhaving a positive factor needed to remove the ghosts. Taking f(R,T)=R+2βT, 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(ϕ) =λϕ^4 and the small field inflation V(ϕ) =V_0(1- (\fracϕμ)^α). 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

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

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

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 $ω_q$ 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 $χ_0=\frac{P_cv_c}{T_c}=\frac{27-3\sqrt{6}}{50}$, 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 $ω_q$, 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↗