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Ahmad Al-Badawi

Publications and source records attributed to Ahmad Al-Badawi.

At least 37 records · Page 2Linked to original sources
arXiv2026

Shadow, Sparsity of Radiation and Energy Emission Rate in Skyrmion Black Holes

We examine several observable optical properties of a Skyrmion black hole (BH), focusing on the photon sphere, BH shadow, and photon trajectories. The Skyrme term, along with other geometric parameters of the spacetime, determines the photon sphere location and shapes the resulting BH shadow. Parameter variations produce observable departures from standard BH geometries, offering potential signatures of nonlinear field effects. We also analyze the sparsity of Hawking radiation and the associated energy emission spectra, showing how these quantities respond to the Skyrme coupling and background parameters. Our findings illuminate the connection between nonlinear field contributions and BH optics, with implications for observational and theoretical studies of modified gravity scenarios.

gr-qc↗
arXiv2026

Plummer Dark Matter Black Hole with Topological Defects: Shadow, Greybody Factors, Quasinormal Modes, and Thermodynamics

We construct a static, spherically symmetric black hole (BH) solution embedded in a cored Plummer dark matter (DM) halo and a Letelier cloud of strings (CoS). Starting from the Plummer-Schwarzschild metric of Senjaya et al.~\cite{Senjaya2026}, we incorporate the string-cloud tension parameter $α$ into the lapse function, obtaining $A(r) = h_{\rm Plummer}(r) - α$. The resulting spacetime admits a single, non-degenerate event horizon (EH) for $α< 1$ and a naked singularity for $α\ge 1$. We determine the photon sphere (PS) and BH shadow radii, compute the weak deflection angle via the Gauss-Bonnet theorem (GBT), and analyze the innermost stable circular orbit (ISCO). Scalar perturbations are studied through the effective potential, greybody factor (GF) bounds obtained from the Boonserm-Visser method, the Hawking emission spectrum, and quasinormal mode (QNM) frequencies computed with the WKB approximation. The thermodynamic analysis covers the Hawking temperature, Bekenstein-Hawking entropy, heat capacity, and Gibbs free energy; the heat capacity is found to be strictly negative for all parameter values, confirming the absence of any Davies-type phase transition. A consistent hierarchy emerges across all six analyses: the CoS tension $α$ governs the leading-order modifications to every observable, while the Plummer halo density $ρ_0$ provides a subdominant, additive correction.

gr-qc↗
arXiv2026

Observational imprints and quasi-Periodic oscillations of magnetically charged anti-de Sitter black holes

In this work, we investigate observable signatures of a magnetically charged Anti-de Sitter black hole in string-inspired Euler-Heisenberg theory. We analyze photon trajectories, the photon sphere, and the resulting black hole shadow. We derive the photon sphere and shadow radii and show that both deviate from the Schwarzschild and Schwarzschild-AdS cases. In particular, the radii decrease monotonically as the magnetic charge parameter $Q_m$ increases, indicating that magnetic charge modifies light propagation near the black hole. We also study neutral and charged particle motion and compute the corresponding epicyclic frequencies. Using the effective potential method, we obtain the specific energy and angular momentum for stable circular orbits and determine the innermost stable circular orbit (ISCO). The presence of $Q_m$ shifts the ISCO radius and alters the orbital structure. The radial, vertical, and orbital frequencies show clear deviations from the Schwarzschild case. Finally, we confront the model with twin-peak quasi-periodic oscillation (QPO) data from stellar-mass, intermediate-mass, and supermassive black hole candidates. A two-dimensional Delta chi-square analysis in the ($r$, $Q_m$) space shows that the best fit corresponds to $Q_m=0$, although finite values remain allowed within confidence levels. At the 1 sigma level, we obtain an upper bound $Q_m/M$ less than about 0.2. These results indicate that while magnetic charge produces measurable theoretical deviations, current QPO data place only moderate constraints on its magnitude.

gr-qc↗
arXiv2026

Screened Simpson-Visser Black Holes with Asymptotically de-Sitter Core

In this work, we introduce a screened Simpson-Visser regular solution and perform a comprehensive study of its physical and observational properties. We begin by analyzing the thermodynamic behavior of the black hole, including detailed investigations of the Hawking temperature, Gibbs free energy, and specific heat, which provide insights into its stability and phase structure. Next, we examine the geodesic structure of the spacetime, considering both massless (photon) and massive (timelike) particles. In particular, we study the photon sphere, the corresponding black hole shadow, and the innermost stable circular orbits (ISCO), which are crucial for understanding the motion of matter and light around the black hole. Furthermore, we explore the black hole's energy-emission rate radiation, highlighting the effects of the modified geometry on observational signatures. Finally, we investigate the topological aspects of the black hole, analyzing both the thermodynamic topology and the photon sphere's topological properties. Our analysis demonstrates the intricate interplay between the spacetime geometry, geodesic motion, and black hole thermodynamics, offering a deeper understanding of this class of regular black holes and their potential observational consequences.

gr-qc↗
arXiv2026

Thermodynamics and Optical Properties of Charged Black Holes in Bumblebee gravity Sourced by a Cloud of Strings

In theories where the Lorentz symmetry of gravity is spontaneously broken, a non-minimally coupled bumblebee vector field acquires a nonzero vacuum expectation value, leading to modifications of standard General Relativity (GR). In this work, we investigate exact solutions describing static and spherically symmetric charged black holes surrounded by a cloud of strings within the framework of bumblebee gravity. We begin by analyzing the thermodynamic properties of these black hole solutions, including their mass, temperature, and entropy, highlighting how Lorentz-violating effects alter standard results. Next, we examine the optical properties of the spacetime, focusing on the photon sphere, the resulting black hole shadow, and the deflection of light, thereby providing potential observational signatures of Lorentz violation. Finally, we explore the impact of Lorentz-violating parameters on classical gravitational tests within the Solar System, such as advance of perihelion precession, in order to set observational constraints. Our analysis provides a comprehensive investigation of the interplay between Lorentz violation, black hole physics, and cloud of strings, offering a framework to probe new physics beyond GR.

gr-qc↗
arXiv2026

Accelerating Bertotti-Robinson Black Holes in a Uniform Magnetic Field

We study the Hawking temperature, geodesic motion, and observable signatures of the accelerating Bertotti-Robinson (BR) spacetime, a vacuum black-hole solution deformed by a uniform magnetic field $B$ and an acceleration parameter $α$. In the timelike sector, we derive the effective potential for massive particles, determine the specific energy and angular momentum for equatorial circular orbits, and determine how $(B,α)$ shifts the ISCO; we also illustrate representative trajectories of massive particles. We then compute the radial and latitudinal epicyclic frequencies for small perturbations about circular orbits, quantifying how the magnetic field and acceleration modify local radial and vertical stability. In the null sector, we derive the photon effective potential and obtain analytical expressions for the photon-sphere radius, critical impact parameter, and shadow radius, complemented by photon trajectories, the effective radial force, and the Lyapunov exponent controlling the instability of circular null orbits; we also provide parameter-space maps for the photon sphere and shadow. Finally, we obtain the energy emission rate emitted from the black hole, showing how the acceleration parameter and the magnetic field affect this.

gr-qc↗
arXiv2026

$P$--$V$ criticality, Joule--Thomson expansion, and holographic heat engine of charged Hayward-AdS black holes with a cloud of strings and perfect fluid dark matter

We construct the charged Hayward-anti-de Sitter (AdS) black hole (BH) with a cloud of strings (CS) and perfect fluid dark matter (PFDM), and analyze its extended thermodynamic phase structure. The Hayward parameter $g$ replaces the central singularity with a de Sitter (dS) core, while the CS parameter $a$ and the PFDM parameter $β$ encode astrophysically motivated matter content. Treating the cosmological constant as pressure, we derive the thermodynamic quantities, verify the Smarr relation, and establish $P$--$V$ criticality with a van der Waals (vdW)-like small-large BH phase transition and mean-field critical exponents. The Gibbs free energy (GFE) exhibits the characteristic swallowtail below the critical pressure. The Joule-Thomson (JT) expansion yields $T_i^{\rm min}/T_c \approx 0.247$, roughly half the Reissner--Nordström-AdS value. The parameters $g$ and $Q$ contract the cooling region, $β$ expands it, and $a$ reshapes it non-monotonically. A holographic heat engine with a rectangular cycle gives efficiencies $η= 0.362$--$0.396$ and Carnot benchmarking ratios $η/η_C = 0.625$--$0.791$ across six configurations. The CS parameter improves the engine efficiency by reducing the enthalpy at fixed thermodynamic volume, while the PFDM parameter degrades it by adding gravitational enthalpy without contributing to the mechanical work.

gr-qc↗
arXiv2026

Some phenomenological aspects of a quantum-corrected Reissner-Nordström black hole: quasi-periodic oscillations, scalar perturbations and thermal fluctuations

In this work, we investigate several phenomenological aspects of a covariant quantum-corrected Reissner-Nordström black hole characterized by the mass $M$, electric charge $Q$, and the quantum correction parameter $ζ$. We first study the motion of neutral test particles and derive the fundamental orbital and epicyclic frequencies, which are then employed to analyze different quasi-periodic oscillation (QPO) models. Using observational QPO data from stellar-mass, intermediate-mass, and supermassive black hole candidates, we perform a Bayesian parameter estimation through a Markov Chain Monte Carlo (MCMC) analysis and obtain constraints on the black hole parameters. The results show that the presence of the quantum correction significantly affects the location of the QPO radii and the separation between the QPO orbit and the ISCO. We then examine the scalar perturbations by deriving the Schrödinger-like radial equation and the corresponding effective potential. The influence of the parameters $Q$ and $ζ$ on the perturbation potential and stability of the spacetime is discussed. Furthermore, we compute the greybody factor and the energy emission rate in the high-frequency (geometric-optics) regime, showing how the quantum correction modifies the absorption probability and radiation spectrum. Finally, we study the effect of thermal fluctuations on the black hole entropy and obtain the logarithmic corrections to the Bekenstein-Hawking area law. We show that these corrections become important for small black holes, while for large horizon radius the standard thermodynamic behavior is recovered. Our analysis demonstrates that the quantum correction parameter leaves observable imprints on both dynamical and thermodynamical properties of the spacetime and can be constrained through QPO observations.

gr-qc↗
arXiv2026

ModMax-AdS Black Hole with Global Monopole as Source in Kalb-Ramond Gravity

In this work, we investigate in detail the thermodynamic properties of a spherically symmetric ModMax-AdS black hole sourced by a global monopole within the Kalb-Ramond gravity. We derive the key thermodynamic quantities, including the Hawking temperature, Gibbs free energy, and specific heat capacity, and analyze how the geometric parameters influence these physical quantities. The first law of thermodynamics and the corresponding Smarr formula are explicitly verified. Furthermore, we study the thermodynamic criticality of the system by deriving the critical points and examining the effects of the space-time geometric parameters. We also obtain the inversion temperature and demonstrate that the minimum inversion temperature is modified by the space-time parameters. In addition, the sparsity of Hawking radiation and thermal fluctuations of the system are investigated, highlighting the effects of the parameters on the entropy corrections. Finally, we analyze the optical properties of the black hole, in particular the photon sphere and shadow radius, showing how these parameters influence these features.

gr-qc↗
arXiv2026

Thermal Analysis, Joule-Thomson Expansion and Hawking Sparsity of Mod(A)Max-AdS Black Hole Immersed in a Cloud of Strings

We investigate the thermodynamic behavior of a spherically symmetric Anti-de Sitter black hole in Mod(A)Max electrodynamics surrounded by a cloud of strings. Within the extended phase-space framework, we treat the cosmological constant as a pressure and interpret the black-hole mass as enthalpy, which enables a unified discussion of local stability, global phase structure, and Joule--Thomson expansion. We analyze the Hawking temperature, Gibbs free energy, and heat capacity, and show how the string-cloud parameter, the Mod(A)Max deformation, and the electric charge reshape the physical domain, the stability windows, and the small/large black-hole transition pattern. We further characterize the critical behavior and demonstrate that a van der Waals--like phase structure arises only in the physical sector, while the alternate branch does not admit a genuine critical point. For the Joule-Thomson process, we determine the inversion curve and the corresponding isenthalpic trajectories, highlighting how the model parameters control the cooling/heating regimes and can generate terminating isenthalpic behavior at sufficiently large charge. Finally, we examine the sparsity of Hawking radiation and discuss how the underlying parameters influence the temporal discreteness of the emitted flux, particularly near extremality and in the large-radius AdS regime.

physics.gen-ph↗
arXiv2026

Geodesic Structure, Thermodynamics and Scalar Perturbations of Mod(A)Max black hole Surrounded by Perfect Fluid Dark Matter

In this work, we investigate the optical properties of a spherically symmetric Mod(A)Max black hole surrounded by perfect fluid dark matter, focusing on key features such as the photon sphere radius, shadow, photon trajectories, and the effective radial force experienced by photons. We also study the dynamics of massive particles around the black hole, deriving the effective potential and, from it, the specific energy and angular momentum of particles moving in circular orbits of fixed radii is discussed. The conditions for marginally stable circular orbits are analyzed, highlighting how the geometric parameters that modify the spacetime curvature influence both the optical and dynamical features. Furthermore, we explore the thermodynamic behavior of the black hole by examining its temperature, Gibbs free energy, and heat capacity, as well as its thermodynamic topology. Finally, scalar field perturbations are considered through the massless Klein-Gordon equation, and the quasinormal modes (QNMs) in the eikonal regime are computed, illustrating how the geometric parameters affect the potential and the QNM spectra.

gr-qc↗
arXiv2026

Thermodynamics and shadow of Simpson-Visser black hole with phantom global monopoles

We investigate the thermodynamics and shadow of a non-rotating Simpson Visser black hole with a phantom global monopole. The model is governed by three parameters: the coupling constant $ξ$, the energy scale of symmetry breaking $η$, and the bounce parameter $a$, which jointly influence horizon structure and observational signatures. Using specific heat and free-energy analysis, we show that small-horizon configurations are locally thermodynamically stable but never globally favored. Analytical solutions of null geodesics reveal that the photon sphere radius depends on the bounce parameter $a$ and the energy scale of symmetry breaking $η$, while the critical impact parameter is still unaffected by $a$. Moreover, the photon sphere radius and critical impact parameter, showing that increasing $η$ enlarges both quantities for an ordinary global monopole, while reducing them in the phantom case. Our results highlight how the bounce parameter and phantom global monopole significantly alter the black hole's physical and geometric properties.

gr-qc↗
arXiv2026

Observable Optical Signatures, Particle Dynamics and Epicyclic Frequencies of Mod(A)Max Black Holes

In this work, we investigate the observable optical signatures of the Mod(A)Max black hole spacetime. We analyze key optical features, including the photon sphere, black hole shadow, and photon trajectories, and examine how these observables depend on the underlying geometric parameters, such as the electric charge and the Mod(A)Max coupling parameter. We further study the dynamics of neutral test particles in the vicinity of the black hole by deriving the effective potential within the Hamiltonian formalism. Using this potential, we obtain the specific energy and specific angular momentum for test particles on circular orbits of fixed radius, as well as the innermost stable circular orbit (ISCO), and explore how the geometric parameters influence these quantities and the ISCO radius. Finally, we derive the epicyclic (azimuthal, radial, and vertical) frequencies to analyze quasi-periodic oscillations (QPOs) exploring how the geometric parameters influences these and discuss their physical implications.

gr-qc↗
arXiv2026

Probing the Charged Hayward Black Hole in Dark Matter and String Cloud Environments through Shadow, Geodesics, and Quasinormal Spectrum

We construct a charged Bardeen black hole (BH) surrounded by perfect fluid dark matter (PFDM) and coupled to a cloud of strings (CS). The metric function combines the magnetic monopole charge from nonlinear electrodynamics, the PFDM logarithmic correction, and the CS parameter that renders the spacetime asymptotically non-flat. We analyze the horizon structure, identifying parameter ranges yielding non-extremal BHs, extremal configurations, and naked singularities. The null geodesics, photon sphere radius, and shadow are computed, revealing that both CS and PFDM enlarge the shadow. For neutral particle dynamics, we derive the specific energy, angular momentum, and innermost stable circular orbit location. Quasiperiodic oscillations (QPOs) are examined through the azimuthal, radial, and vertical epicyclic frequencies, where notably the azimuthal frequency is independent of the CS parameter. Scalar field perturbations governed by the Klein-Gordon equation yield an effective potential whose peak decreases with both parameters, yet the transmission and reflection probabilities respond oppositely to CS and PFDM variations. The greybody factor bounds are obtained using semi-analytical methods. Our results demonstrate that the distinct effects of $α$ and $β$ on various observables could allow independent constraints on these parameters through shadow measurements, QPO timing, and gravitational wave ringdown observations.

gr-qc↗
arXiv2026

Observational signatures of charged Bardeen black holes in perfect fluid dark matter with a cloud of strings

We construct a charged Bardeen black hole (BH) surrounded by perfect fluid dark matter (PFDM) and coupled to a cloud of strings (CS). The metric function combines the magnetic monopole charge from nonlinear electrodynamics, the PFDM logarithmic correction, and the CS parameter that renders the spacetime asymptotically non-flat. We analyze the horizon structure, identifying parameter ranges yielding non-extremal BHs, extremal configurations, and naked singularities. The null geodesics, photon sphere radius, and shadow are computed, revealing that both CS and PFDM enlarge the shadow. For neutral particle dynamics, we derive the specific energy, angular momentum, and innermost stable circular orbit location. Quasiperiodic oscillations (QPOs) are examined through the azimuthal, radial, and vertical epicyclic frequencies, where notably the azimuthal frequency is independent of the CS parameter. Scalar field perturbations governed by the Klein-Gordon equation yield an effective potential whose peak decreases with both parameters, yet the transmission and reflection probabilities respond oppositely to CS and PFDM variations. The greybody factor bounds are obtained using semi-analytical methods. Our results demonstrate that the distinct effects of $α$ and $β$ on various observables could allow independent constraints on these parameters through shadow measurements, QPO timing, and gravitational wave ringdown observations.

gr-qc↗
arXiv2026

Effects of spontaneous Lorentz Symmetry breaking on Letelier-AdS charged black holes within Kalb-Ramond gravity

In this study, we investigate the geodesic motion of massless particles -- specifically photons -- in the spacetime of a charged anti-de Sitter (AdS) black hole (BH) surrounded by a cloud of strings (CoS) within the framework of Kalb-Ramond (KR) gravity. We analyze the effective potential that governs photon trajectories, explore the properties and location of the photon sphere (PS), and examine the effective radial force acting on photons. The resulting BH shadow is also studied, highlighting the roles of both the CoS parameter $α$ and the KR field parameter $\ell$ in shaping its geometry. We constrain these parameters using observational data from M87* and Sgr A* obtained by the Event Horizon Telescope (EHT). Furthermore, we extend our investigation to the motion of neutral test particles in the same gravitational background. By examining the impact of the CoS and KR field, we show how these additional fields modify the dynamics relative to standard charged BH scenarios. Finally, we study the fundamental frequencies associated with quasiperiodic oscillations (QPOs) of test particles, demonstrating how these frequencies are affected by the presence of the CoS and KR field. Our results reveal the rich structure of AdS-BH spacetimes influenced by string clouds and antisymmetric tensor fields, with potential observational consequences in gravitational wave and BH imaging astronomy.

gr-qc↗
arXiv2026

Charged Simpson-Visser AdS Black Holes: Geodesic Structure and Thermodynamic Properties

In this article, we apply the Simpson-Visser (SV) regularization scheme to Anti-de Sitter (AdS) charged black holes and investigate the resulting spacetime geometry in detail, with emphasis on both geodesic structure and thermodynamic behavior. In particular, we analyze the motion of massless particle, focusing on key features such as the photon sphere, black hole shadow, photon trajectory and the dynamics of charged particles, including the characteristics of the circular and type of orbits. Furthermore, we compare the theoretical predictions of the charged SV-AdS black hole with recent observations reported by the Event Horizon telescope (EHT) for M87* and Sgr~A*. Beyond the geodesic analysis, we explore the thermodynamics of the regularized charged SV-AdS black hole by deriving essential quantities such as the Hawking temperature, Gibbs free energy, and specific heat capacity. Through a systematic examination of these thermodynamic variables, we demonstrate how the regularization parameter inherent in the SV regularization influences particle dynamics, stability conditions, and the overall thermal properties of the modified black hole solution. This comprehensive study highlights the interplay between regularization effects and the physical observables associated with charged AdS black holes.

gr-qc↗
arXiv2025

Optical appearance, Hawking radiation, and Barrow thermodynamics of Letelier black hole in electromagnetic universe

We present an investigation of a static, spherically symmetric Letelier black hole (BH) immersed in an electromagnetic universe (EMU), characterized by the cloud of strings (CoS) parameter $α$ and the EMU parameter $a$. The photon sphere and shadow radius are derived analytically, revealing how both parameters modify the apparent BH silhouette compared to the Schwarzschild case. We extend the shadow analysis to homogeneous and inhomogeneous plasma environments, demonstrating systematic reductions in the observed shadow size, and compute the weak gravitational lensing deflection angle in plasma using the Gauss-Bonnet theorem. The perturbative dynamics are investigated for scalar, electromagnetic, and Dirac fields, with quasinormal mode frequencies obtained via the sixth-order WKB approximation and greybody factors calculated using the rigorous bounds method. The resulting Hawking radiation spectra reveal distinct signatures for bosonic and fermionic emission channels. We further analyze quasi-periodic oscillations by deriving the fundamental orbital frequencies and applying both parametric resonance and relativistic precession models, obtaining constraints from observations.

gr-qc↗