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Faizuddin Ahmed

Publications and source records attributed to Faizuddin Ahmed.

At least 73 records · Page 4Linked to original sources

Comment on "Black hole in Dehnen $(1,\,4,\,\frac{1}{2})$ dark matter halo: exact solution, lensing, light ring, and thermodynamics (EPJC 85 (2025) 1256)"

In a recent article, the author of Ref. [EPJC 85 (2025) 1256] constructed an exact solution describing a static, spherically symmetric black hole embedded in a Dehnen-($α, β, γ$) type dark matter halo with the parameter choice $α=1,\,β=4,\,γ=1/2$. The author first derived the density profile, which was subsequently integrated to obtain the mass profile, and this mass profile was then employed in constructing the exact metric solution. In this comment, we demonstrate that both the density profile and the mass profile obtained in Ref. [EPJC 85 (2025) 1256] contain fundamental mathematical errors that invalidate the subsequent analysis.

gr-qc↗

Kerr-Bertotti-Robinson Black Holes Surrounded by a Cloud of Strings

In a recent study [1], authors introduced a new class of exact space-times in Einstein's gravity, which are Kerr black holes immersed in an external uniform magnetic field that is oriented along the rotational axis. Motivated by this work, we investigate a Kerr-like black hole solution with a cloud of strings surrounded by a uniform magnetic field. For the zero rotation case, the space-time reduces to the Schwarzschild-Bertotti-Robinson black hole with a cloud of strings. Moreover, for zero magnetic field, the metrics simplify to a Kerr-like black hole surrounded by a cloud of strings, and its static counterpart reduces to the Schwarzschild black hole with a cloud of strings.

gr-qc↗

Spherically Symmetric Quantum-Corrected Black Holes with String Clouds: A Multi-Observable Analysis

We present an investigation of quantum-corrected black hole spacetimes coupled with clouds of strings, examining two distinct theoretical models that incorporate quantum gravitational effects through different implementations of correction terms. Our study explores the geodesic structure, focusing on photon sphere properties, black hole shadows, and innermost stable circular orbits of test particles around these exotic geometries. The analysis reveals fundamental modifications to particle trajectories that distinguish quantum-corrected solutions from their classical counterparts, with observable implications for high-energy astrophysics. We investigate quasi-periodic oscillations arising from test particle motion, deriving frequency relationships that could serve as observational probes of quantum gravity effects in accreting black hole systems. Through rigorous gravitational lensing analysis using the Gauss-Bonnet theorem, we calculate weak-field deflection angles and identify distinctive signatures that enable discrimination between the two quantum correction models. The gravitational lensing study reveals opposite dependencies on quantum parameters between the models, providing unambiguous observational discriminants. Additionally, we analyze the thermodynamic properties including temperature, entropy, and heat capacity modifications, exploring topological characteristics and phase transition behavior in these quantum-corrected systems. The investigation reveals that the two models exhibit contrasting behaviors across multiple observational channels, from gravitational lensing deflection angles to quasi-periodic oscillation frequencies, providing remarkable discriminants for testing quantum gravity theories.

astro-ph.HE↗

Perturbations and Greybody Factors of AdS Black Holes with a Cloud of Strings Surrounded by Quintessence-like Field in NLED Scenario

The discovery of gravitational waves and advances in black hole imaging have opened new opportunities to probe exotic physics in strong-field regimes. Building upon a recent black hole solution in Einstein gravity coupled with nonlinear electrodynamics and exotic matter sources-specifically a cloud of strings and a quintessence field--we study the perturbative dynamics, thermodynamic behavior, and quantum transmission characteristics in anti-de Sitter spacetime. The black hole, defined by its mass, nonlinear magnetic charge, string cloud, and quintessence parameters, exhibits modified spacetime geometry, horizon structure, Hawking temperature, and effective potentials governing field propagation. We derive Schrödinger-like equations for massless scalar, electromagnetic, and fermionic perturbations, exploring how these sources jointly shape the potential barriers. The Hawking temperature shows strong dependence on the horizon radius and nonlinear charge, differing markedly from asymptotically flat cases due to the cosmological constant. Greybody factors, describing Hawking radiation transmission probabilities, are computed for all field spins via turning point analysis. A notable result arises in the fermionic sector: positive and negative helicity modes attain maximal transmission at distinct quintessence normalization values, revealing helicity-dependent coupling absent in bosonic channels. This asymmetry suggests a potential observational signature of spin-exotic matter interactions, offering new insights into detecting quintessence through black hole radiation spectra. Our results extend previous perturbative analyses by incorporating nonlinear electrodynamics, cosmic strings, and quintessence effects--linking quantum radiation studies to gravitational wave astronomy and early-universe cosmology.

hep-th↗

Letelier-AdS Black Hole Surrounded by a Perfect Fluid Dark Matter in the presence of Quintessence

This study investigates a Schwarzschild-anti de Sitter black hole coupled to a cloud of strings featuring only the electric-like component of the string bivector, embedded in a perfect fluid dark matter and a quintessence field. We examine the dynamics of photons and massive particles, focusing on trajectories, photon spheres, BH shadows, their topological characteristics, and innermost stable circular orbits (ISCOs), and emphasizing the influence of string cloud, perfect-fluid dark matter, and quintessence-like field parameters. Additionally, we explore the black hole's thermodynamics, deriving the Hawking temperature, Gibbs free energy, and specific heat, and discuss the modified first law of thermodynamics and thermodynamic topology under external matter fields. We demonstrate that the presence of a string cloud, perfect-fluid dark matter, and a quintessence-like field together modifies the geodesic structure and thermodynamic properties, thereby shifting the results relative to the standard Schwarzschild BH solution.

gr-qc↗

Single-Scale Magnetoelastic Landau Quantization: Thermodynamics, Quantum Oscillations, and Metrology

We develop a unified, single-scale description of thermodynamics and quantum oscillations in electronic systems with a uniform areal density of screw dislocations under a uniform magnetic field. A single tunable gap, $\hbar|ω_{eff}|$ with $ω_{eff}=ω_{c}+ω_{cl}$, organizes all equilibrium observables obtained from a compact harmonic-oscillator partition function: free energy, internal energy, entropy, heat capacity, magnetization, magnetic susceptibility, and magnetocaloric responses collapse onto universal hyperbolic kernels in $x=\hbar|ω_{eff}|/(2k_{B}T)$. We identify a compensated-field regime where the transverse gap closes and the heat capacity reaches an equipartition plateau, providing a sharp signature of magnetoelastic interference. In transport and torque, the same scale rigidly shifts the Hall fan and compresses the $1/B$ period of de Haas-van Alphen and Shubnikov-de Haas oscillations when expressed in $1/B_{eff}$, enabling a phase-unwarping protocol that metrologizes the dislocation density from a single field sweep. In mesoscopic samples, boundary corrections to the Landau degeneracy generate finite-size calorimetric oscillations that diagnose the effective magnetic length. Moderate disorder and weak interactions preserve the kernel structure while smoothing amplitudes. We outline an experimental roadmap combining on-chip calorimetry, torque magnetometry, and transport, and discuss device-level opportunities in caloritronics and strain engineering, magnetocaloric microcooling, magnetoelastic heat switching, and dilatometric transduction, where the single scale $\hbar|ω_{eff}|$ enables rational design and optimization.

cond-mat.mes-hall↗

Schwarzschild Black Hole Coupled with a Cloud of Strings Immersed in King Dark Matter Halo

In this paper, we examine the geodesic and thermodynamic properties of a Schwarzschild black hole with a cloud of strings (known as the Letelier black hole) immersed in a King dark matter (KDM) halo under an isotropic configuration. The dynamics of both photons and massive particles are analyzed in detail using the effective potential formalism, including particle trajectories, the photon sphere, black hole shadow, and the innermost stable circular orbits (ISCOs). Particular emphasis is placed on how the presence of the KDM halo modifies these geometric and dynamical features. Furthermore, we explore the topological characteristics of photon rings by constructing a normalized vector field, following Duan\textquotesingle{}s topological current $ϕ$-mapping theory, and demonstrate how this field is influenced by both the string cloud and the KDM halo. In the thermodynamic context, we analyze the impact of the KDM halo and the string cloud on the Hawking temperature, Gibbs free energy, thermal stability, and phase transitions of the black hole. Finally, we examine the thermodynamic topology of the system using a theoretical framework that incorporates a generalized Helmholtz free energy and topological current theory. In both the photon sphere and thermodynamic analyses, we show that the string cloud parameter shifts the location of the zero point of the vector field in the equatorial plane. Specifically, in the photon sphere case, the radius of the photon sphere increases with increasing values of the string cloud parameter, while in the thermodynamic topology, the horizon radius decreases as the string cloud parameter increases.

gr-qc↗

Nonrelativistic quantum dynamics in a twisted screw spacetime

We investigate the nonrelativistic quantum dynamics of a spinless particle in a screw-type spacetime endowed with two independent twist controls that interpolate between a pure screw dislocation and a homogeneous twist. From the induced spatial metric we build the covariant Schrödinger operator, separate variables to obtain a single radial eigenproblem, and include a uniform magnetic field and an Aharonov-Bohm (AB) flux by minimal coupling. Analytically, we identify a clean separation between a global, AB-like reindexing set by the screw parameter and a local, curvature-driven mixing generated by the distributed twist. We derive the continuity equation and closed expressions for the azimuthal and axial probability currents, establish practical parameter scalings, and recover limiting benchmarks (AB, Landau, and flat space). Numerically, a finite-difference Sturm-Liouville solver (with core excision near the axis and Langer transform) resolves spectra, wave functions, and currents. The results reveal AB periodicity and reindexing with the screw parameter, Landau-fan trends, twist-induced level tilts and avoided crossings, and a geometry-induced near-axis backflow of the axial current with negligible weight in cross-section integrals. The framework maps the geometry and fields directly onto measurable spectral shifts, interferometric phases, and persistent-current signals.

quant-ph↗

Black Hole Solution in Anti-de Sitter Space with a New Cloud of Strings Surrounded by Dark Matter Halo

This paper presents a comprehensive theoretical study of a Schwarzschild-like Anti-de Sitter (AdS) black hole (BH) influenced by a new cloud of strings (NCS) and a dark matter halo (DMH) characterized by a Dehnen-type density profile. We analyze the geodesic motion of both massless and massive test particles, highlighting how the NCS and DMH parameters affect the effective potentials, photon spheres, circular orbits, BH shadow, and the innermost stable circular orbit (ISCO) of test particles. Additionally, we investigate the thermodynamic behavior of the BH in an extended phase space by deriving key quantities, such as the Hawking temperature, the equation of state (EoS), Gibbs free energy, internal energy, and the specific heat capacity. Our results show that the presence of NCS and DMH induces significant modifications in both the dynamical and thermodynamical behavior of the BH, including shifts in the Hawking-Page transition and divergences in heat capacity, thereby reshaping the phase structure of the BH.

gr-qc↗

Static AdS Black Holes Surrounded by Strings and Quintessence-like Field within Rastall Gravity Framework

In this work, we tested the physical properties of Rastall black holes in the presence of string clouds and quintessence. The modified spacetime geometry arising from the Rastall framework is first established, providing the basis for analyzing the geodesic structure. We study null geodesics in detail, testing photon trajectories, the conditions for photon spheres, BH shadows, the associated effective radial force, and the topological features of photon rings. Also, the analysis is further tested to timelike geodesics, where we investigate the motion of massive particles and determine the innermost stable circular orbits. In this case, we discuss the thermodynamic behavior of the system, show the effects of Rastall gravity, strings, and quintessence on the BHs stability and thermal characteristics. In this context, our results improve and show of how modifications to general relativity and surrounding matter distributions influence both the dynamical and thermodynamical aspects of BHs.

gr-qc↗

AdS Black Hole Solution with a Dark Matter Halo Surrounded by a Cloud of Strings

We derive and analyze a Schwarzschild-like Anti-de Sitter (AdS) black hole (BH) obtained as a static, spherically symmetric solution of Einstein's equations sourced by a cloud of strings (CoS) and a dark matter (DM) halo modeled by a Dehnen-type density profile. We first study the geodesic motion of massless and massive test particles, emphasizing how the CoS parameter $α$ and the DM halo parameters $(ρ_s, r_s)$ influence photon spheres, circular orbits, the BH shadow, and the innermost stable circular orbit (ISCO). We then examine scalar perturbations via the effective potential and the associated quasinormal-mode (QNM) spectra, showing how $α$ and $(ρ_s, r_s)$ deform oscillation frequencies and damping rates, thereby affecting stability diagnostics. Furthermore, we investigate the thermodynamics in the extended phase space, deriving the Hawking temperature, equation of state, Gibbs free energy, and specific heat capacity, and establishing a consistent first law and Smarr relation with natural work terms for $α$ and $(ρ_s, r_s)$. We find that the interplay between the CoS and the DM halo produces quantitative and sometimes qualitative changes in both dynamical and thermodynamical properties, including shifts of the Hawking--Page transition and heat-capacity divergences, thus reshaping the phase structure of Schwarzschild--AdS BHs.

gr-qc↗

Dynamics of test particles, QPOs and thermodynamics of charged Euler-Heisenberg AdS black holes with a cloud of strings and dark matter

We investigate the geodesic motion of test particles around a charged Euler-Heisenberg Anti-de Sitter black hole (CEH-AdS-BH) with a cloud of strings (CoS) and surrounded by perfect fluid dark matter (PFDM). Our analysis examines how the interplay between Euler-Heisenberg nonlinear electrodynamic corrections, string cloud, and PFDM distributions modifies fundamental BH properties. We study dynamics of both massless photons and massive neutral test particles, deriving the effective potentials and trajectory equations that govern particle motion in this exotic spacetime. The photon sphere analysis shows systematic increases in shadow radii with string cloud parameter variations, while innermost stable circular orbit (ISCO) calculations demonstrate competing effects between string-induced gravitational weakening and electromagnetic charge contributions. We examine scalar and electromagnetic field perturbations using the Klein-Gordon and Maxwell equations, establishing the perturbative potentials that characterize wave propagation in the modified background. The scalar perturbative potential exhibits characteristic barrier structures influenced by all exotic matter components, while electromagnetic perturbations show fundamental differences due to their vector nature. Our thermodynamic investigation extends the conventional framework by incorporating additional intensive variables corresponding to cosmic string and perfect fluid dark matter contributions. The specific heat capacity analysis reveals divergence points that demarcate thermodynamically stable and unstable regions, while the Gibbs free energy exhibits modified profiles that extend Anti-de Sitter black hole thermodynamics into new parameter regimes.

gr-qc↗

Analytic and Numerical Constraints on QPOs in EHT and XRB Sources Using Quantum-Corrected Black Holes

This investigation examines QPOs in two quantum-corrected BH spacetimes that preserve general covariance while incorporating quantum gravitational effects through a dimensionless parameter ζ. We combine analytical derivations of epicyclic frequencies with comprehensive numerical simulations of BHL accretion to explore how quantum corrections manifest in observable astrophysical phenomena. Using a fiducial BH mass of M=10M_\odot representative of stellar-mass X-ray binaries, we demonstrate that the two models exhibit fundamentally different behaviors: Model-I modifies both temporal and radial metric components, leading to innermost stable circular orbit migration proportional to ζ^4 and dramatic stagnation point evolution from 27M to 5M as quantum corrections strengthen. Model-II preserves the classical temporal component while altering only spatial geometry, maintaining constant stagnation points and stable cavity structures throughout the parameter range. Our numerical simulations reveal distinct QPO generation mechanisms, with Model-I showing systematic frequency evolution and cavity shrinkage that suppresses oscillations for ζ\geq 3M, while Model-II maintains stable low-frequency modes up to ζ\geq 5M. Power spectral density analyzes demonstrate characteristic frequency ratios (3:2, 2:1, 5:3) consistent with observations from X-ray binaries, providing specific targets for discriminating between quantum correction scenarios. The hydrodynamically derived constraints (ζ\lesssim 4M) show remarkable agreement with independent EHT limits for M87* and Sgr A*, validating our theoretical framework through multiple observational channels. These results establish QPO frequency analysis as a probe for detecting quantum gravitational effects in astrophysical BHs and demonstrate the complementary nature of timing and imaging observations in constraining fundamental physics.

astro-ph.HE↗

Gravitational Lensing and Topological Photon Sphere of Holonomy Corrected Schwarzschild Black Hole with a Cloud of Strings

In this paper, we theoretically investigate the deflection of light, lensing equations, topological properties of photon rings, and accretion disk characteristics in the spacetime of a holonomy-corrected Schwarzschild black hole surrounded by a cloud of strings. The analysis is carried out in the weak-field limit, where we analytically derive expressions for the deflection angle and extract the corresponding lensing observables. These results reveal the dependence of light deflection on the string cloud parameter and the holonomy correction parameter, offering potential observational signatures of underlying quantum gravity effects. We model possible gravitational scenarios to explore the distinguishing features of this modified BH geometry and assess its deviation from classical solutions through gravitational lensing behavior. Furthermore, we analyze the topological structure of the photon sphere by constructing a normalized vector field and demonstrate how it is affected by the presence of string clouds and holonomy corrections. Finally, we examine the properties of a thin accretion disk in this BH background, showing that both the string cloud and holonomy parameters significantly influence the disk's radiation profile, temperature distribution, and spectral characteristics. Our results suggest that these modifications leave measurable imprints, providing viable avenues for observational constraints in the strong-gravity regime.

gr-qc↗

A Black Hole Solution in Kalb-Ramond Gravity with Quintessence Field: From Geodesic Dynamics to Thermal Criticality

We present a theoretical investigation of black hole solutions in Kalb-Ramond gravity embedded with quintessence fields. Our study examines how combined effects of Lorentz violation through the Kalb-Ramond field parameter $η$ and exotic matter contributions via quintessence parameters $(\mathrm{C}, w)$ systematically modify spacetime geometry, particle dynamics, and observational signatures compared to standard Schwarzschild black holes. The analysis encompasses geodesic motion for both photons and massive particles, revealing substantial modifications to effective potentials, photon sphere characteristics, and innermost stable circular orbit properties. We derive analytical expressions for black hole shadow radii across different quintessence states, demonstrating systematic parameter dependencies enabling observational discrimination between theoretical frameworks. Our perturbation analysis of scalar and electromagnetic fields shows how Lorentz violation and quintessence effects alter wave propagation and stability properties. Using Gauss-Bonnet theorem methodology, we calculate gravitational lensing deflection angles incorporating both modified gravity and exotic matter contributions. The thermodynamic investigation reveals complex phase structures with modified Hawking temperature evolution, Gibbs free energy characteristics, and specific heat capacity behavior significantly deviating from general relativity predictions. Lorentz violation amplifies gravitational effects, whereas quintessence exerts counteractive forces, generating complex parameter spaces allowing precise manipulation of observable quantiti

gr-qc↗

Thermodynamics and Joule-Thomson Expansion for Schwarzschild-AdS Black Holes with Cloud of Strings and Quintessential-like Fluid

In this study, we explore the thermodynamic properties of a Schwarzschild black hole (BH) embedded in an anti-de Sitter (AdS) background, which is further coupled with a cloud of strings and surrounded by a quintessence-like fluid. Beginning with the formulation of BH mass in terms of the event horizon radius, we incorporate the concept of pressure as related to the AdS curvature radius within the framework of extended phase space thermodynamics. Using this setup, we derive key thermodynamic quantities, including the Gibbs free energy and internal energy, to characterize the energetic behavior of the black hole system. To assess the stability of the black hole, we compute the specific heat capacity and analyze how it is influenced by external parameters, such as the string cloud and the quintessence-like fluid. These geometric and matter fields are shown to significantly modify the thermal response of the BH. Furthermore, we examine the inversion temperature associated with the black hole and highlight its distinction from the standard Hawking temperature, providing deeper insight into the phase structure. Additionally, we investigate the Joule-Thomson expansion process and demonstrate how the aforementioned parameters affect this thermodynamic phenomenon, showing important aspects of BH cooling and heating behavior in an extended thermodynamic context.

gr-qc↗

Quantum-Corrected Deformation of RN-AdS Black Holes with a Cloud of Strings Immersed in Quintessential-like Fluid

Inspired by Loop Quantum Gravity (LQG), we investigate the Reissner-Nordström (RN) black hole (BH) solution coupled with a cloud of strings in an anti-de Sitter (AdS) background, surrounded by a quintessence-like fluid. We begin by analyzing the optical properties of the BH through null geodesic motion, deriving an effective potential that governs photon dynamics. This effective potential is central to understanding key phenomena such as photon trajectories, circular null orbits, photon sphere, and the resulting BH shadow. Subsequently, we study the dynamics of neutral test particles by deriving effective potential that describes their motion. Using the potential, we compute the specific energy and specific angular momentum of neutral particles in circular orbits around the BH and analyze the outcomes. We also investigate the innermost stable circular orbits (ISCO) and demonstrate how various geometrical and physical properties influence the radius of ISCO. Furthermore, we explore the thermodynamic properties of the BH solution by deriving key quantities such as the Hawking temperature, entropy, Gibbs free energy, internal energy, and specific heat capacity. Throughout the study, we demonstrate that the geodesic structure, scalar field behavior, and thermodynamic properties are significantly influenced by parameters such as the string cloud, quantum correction, electric charge, the surrounding quintessence-like fluid, and the AdS curvature radius.

gr-qc↗

Schwarzschild-AdS Black Holes with Cloud of Strings and Quintessence: Geodesics, Thermodynamic Topology, and Quasinormal Modes

In this study, we explore a Schwarzschild-anti de-Sitter black hole (BH) coupled with a cloud of strings (CoS) possessing both electric- and magnetic-like components of the string bivector, embedded in a Kiselev-type quintessence fluid (QF). We analyze the dynamics of photons and test particles, focusing on trajectories, photon spheres, BH shadows, and innermost stable circular orbits (ISCO), highlighting how CoS and QF parameters affect these features. We then examine the thermodynamic topology of the system by analyzing vector field zeros, showing that varying CoS leads to distinct topological configurations with total charges of either $0$ or $+1$, corresponding to known classes like RN and AdS-RN. Additionally, we study scalar field dynamics via the massless Klein-Gordon equation, reformulated into a Schr$\ddot{o}$dinger-like form to derive the effective potential. We compute the quasinormal modes (QNMs) of scalar perturbations, showing how CoS and QF influence oscillation frequencies and damping rates, with implications for gravitational confinement and thermalization in the AdS/CFT context.

gr-qc↗