arXiv subjects

Faizuddin Ahmed

Publications and source records attributed to Faizuddin Ahmed.

At least 91 records · Page 5Linked to original sources

arXiv2025

Particle Dynamics and Thermal Properties in Kalb-Ramond ModMax Black Holes: Theoretical Predictions for Observational Tests of Exotic Physics

We present a comprehensive theoretical study of geodesic motion and thermodynamic behavior in Kalb--Ramond (KR) black hole (BH) spacetimes sourced by ModMax electrodynamics. Both neutral and charged test particle dynamics are investigated, highlighting how the Lorentz symmetry breaking (LSB) parameter $\ell$, the ModMax nonlinearity parameter $γ$, and the discrete branch parameter $ζ$ significantly modify orbital structures compared to classical Schwarzschild and Reissner--Nordström (RN) solutions. Effective potential analysis reveals notable shifts in the innermost stable circular orbit (ISCO): ordinary branches allow stable orbits closer to the horizon, while phantom branches shift them outward by factors of 5--10. For charged particles, the combined influence of modified gravity and nonlinear electromagnetic fields may induce chaotic trajectories in certain regimes. On the thermodynamic side, we derive full expressions for Hawking temperature, entropy, and Helmholtz free energy. Ordinary branches exhibit divergent specific heat indicating second-order phase transitions, whereas phantom branches yield consistently negative specific heat, implying thermal instability. Phantom BHs are found to possess higher Hawking temperatures and show distinct thermodynamic phase structures, including Hawking--Page-type transitions. Observational features such as BH shadows and gravitational lensing are explored, revealing parameter-dependent changes in photon sphere radii and deflection angles. Notably, the deflection angle analysis via the Gauss--Bonnet theorem method (GBTm) shows opposite-sign electromagnetic corrections for phantom versus ordinary branches, suggesting potential observational discriminants.

gr-qc↗

arXiv2025

Noncommutative Geometry Inspired AdS Black Hole with a Cloud of Strings Surrounded by Quintessence-like fluid

We investigate the geometric and physical properties of an anti-de Sitter (AdS) black hole space-time coupled by a cloud of strings and surrounded by a quintessence-like fluid, all within the framework of non-commutative (NC) geometry. From the perspective of geometrical optics, we analyze the behavior of null geodesics, focusing on key optical features such as the effective potential, the structure and radius of the photon sphere, light deflection angles, photon trajectories, and the resulting black hole (BH) shadow. Our findings show that the combined effects of the string cloud and quintessence-like fluid significantly modify photon dynamics and optical observables, leading to notable deviations from standard BH scenarios in NC geometry background. We also examine time-like geodesics, with particular emphasis on the innermost stable circular orbits (ISCOs). The results demonstrate that the presence of geometric matter components alters the ISCO radius compared to conventional solutions. In addition, we explore the thermodynamic behavior of the BH, deriving expressions for the Hawking temperature, entropy, Gibbs free energy, and specific heat capacity. The influence of the string cloud and quintessence-like fluid introduces substantial modifications to the thermodynamic profile, including shifts in phase transition points and changes to stability conditions under NC geometric effects. Furthermore, we study the dynamics of massless scalar field perturbations in this modified background by formulating the Klein-Gordon equation and reducing it to a Schrödinger-like form via separation of variables. The resulting effective potential is analyzed in detail, highlighting the significant role of both the string cloud and the quintessence-like fluid in shaping the perturbative landscape within the NC geometry setting.

gr-qc↗

arXiv2025

Photon Deflection and Magnification in Kalb-Ramond Black Holes with Topological String Configurations

This theoretical investigation examines gravitational lensing phenomena in Schwarzschild-like black holes (BHs) within Kalb-Ramond (KR) gravity frameworks incorporating cosmic string (CS) and cloud of strings (CoS) topological configurations. We develop comprehensive analytical methodologies for investigating photon deflection angles and magnification characteristics in both Schwarzschild-like BHs in KR gravity pierced by CSs (SKRCS) and Schwarzschild-like BHs in KR gravity with CoS (SKRCoS) spacetime geometries through dual approaches: perturbative expansions yielding approximate solutions and exact elliptic integral formulations providing complete mathematical descriptions across parameter spaces. For CS configurations characterized by Lorentz violation (LV) and CS parameters, deflection angles exhibit systematic modifications through composite geometric factors, while CoS geometries demonstrate distinct deflection characteristics incorporating additional topological parameters that fundamentally alter light propagation dynamics. Magnification analysis reveals distinctive critical curve positioning modifications and amplitude scaling relationships enabling observational discrimination between exotic BH scenarios and conventional spacetime geometries. Strong field analysis utilizing established mathematical frameworks establishes logarithmic divergence coefficients characterizing fundamental scaling behavior in photon sphere proximity regimes. Observational constraints from Solar System precision tests restrict LV parameters within stringent bounds, while galactic-scale observations permit expanded parameter ranges for CS and CoS configurations.

gr-qc↗

arXiv2025

Thermal Behavior of Generalized Black-Bounce Black Hole Model

In this work, we tested the thermal behavior of a class of regular black hole solutions defined as generalized black-bounce spacetimes. We introduce several novel configurations governed by different mass functions and geometric deformations, illustrated by parameters controlling regularity and horizon structure. Using the Hamilton Jacobi tunneling method, we compute the Hawking temperature associated with each model and analyze its dependence on the underlying parameters. We find that all proposed geometries are free of curvature singularities and exhibit positive, well defined quasi-local masses in the Hernandez Misner Sharp formalism. Also, we demonstrate that these models may possess multiple horizons, including extremal and asymmetric cases, while typically violating classical energy conditions in the vicinity of the bounce. Our results show and illustrate the structure and thermodynamic stability of these regular solutions.

gr-qc↗

arXiv2025

Equatorial light bending around a Hairy Kiselev Black Hole

We investigate the deflection angle of light rays confined to the equatorial plane of a Hairy Kiselev black hole. The analysis includes a thorough study of the horizon structure and critical parameters, leading to an analytic expression for the deflection angle in terms of elliptic integrals. Our results confirm that the deflection angle decreases with increasing impact parameter, in agreement with classical predictions of gravitational lensing. The influence of the scalar field, characterized by the coupling constant, shows a nontrivial effect: while moderate values of the coupling constant initially enhance light bending, further increases lead to a suppression of the deflection in the strong-field regime due to modifications in spacetime geometry. Comparative analysis among the Schwarzschild, Kiselev, and Hairy Kiselev black holes indicates that the presence of a quintessential field tends to enhance the deflection, whereas the scalar hair component reduces it. These findings underscore the significant role of scalar fields and exotic matter distributions in shaping light propagation in a modified gravity scenario.

gr-qc↗

arXiv2025

Geodesics, Scalar Fields, and GUP-Corrected Thermodynamics of Charged BTZ-like Black Holes in Bopp-Podolsky Electrodynamics

In Ref. [1], the spacetime geometry generated by compact objects in $(2+1)$-dimensional Bopp-Podolsky electrodynamics is derived. Using a perturbative approach, the authors derived a charged BTZ-like black hole solution and computed corrections up to second order in a perturbative expansion valid far from the horizon. In this work, we investigate the same circularly symmetric three-dimensional charged BH solution pierced by disclinations. We begin by analyzing the motion of photons within this spacetime, focusing on how the geometric parameters influence the effective potential governing null geodesic motion. The corresponding equations of motion are derived, and the resulting orbital dynamics are explored through graphical methods to show the influence of key parameters including the BH mass $M$, electric charge $Q$, cosmological constant $Λ$, and BP coupling parameter $b^2$. Extending our analysis to wave dynamics, we examine the propagation of massless scalar fields in the BH solution by solving the Klein-Gordon equation. Through suitable coordinate transformations, we derive a Schrödinger-like equation with an effective potential that encodes the influence of the topological defect and electromagnetic corrections. Additionally, we investigate quantum gravitational effects by applying the Generalized Uncertainty Principle (GUP) to derive a GUP-corrected Hawking temperature, revealing systematic suppression of thermal radiation that could lead to stable BH remnants. Finally, we compute Keplerian frequencies for circular orbits, demonstrating how the interplay between charge, nonlinear electrodynamics, and disclination parameters creates distinctive observational signatures that could potentially test modified gravity theories in strong-field regimes.

gr-qc↗

arXiv2025

Geometry-induced Coulomb-like potential in helically twisted quantum systems

In this paper, we investigate the Schrödinger equation in a three-dimensional helically twisted space characterized by a non-trivial torsion parameter. By applying exact separation of variables, we derive the radial equation governing the dynamics of quantum particles in this geometric background. Remarkably, the intrinsic coupling between angular and longitudinal momenta induced by the torsion gives rise to an attractive Coulomb-like potential term that emerges purely from the underlying geometry, without introducing any external fields or interactions. We obtain exact analytical solutions for the bound states, including both the energy spectrum and the normalized wave functions. Numerical calculations are also performed, and excellent agreement with the exact results is found. The interplay between the torsion parameter and the effective Coulomb-like interaction is analyzed in detail, showing how geometric deformation generates novel quantum confinement mechanisms in twisted spaces.

quant-ph↗

arXiv2025

Helically twisted spacetime: study of geometric and wave optics, and physical analysis

We analyse a stationary, cylindrically symmetric spacetime endowed with an intrinsic helical twist, $ds^{2} = -dt^{2} + dr^{2} + r^{2} dϕ^{2} + (dz + ω\, r\,dϕ)^{2}$. Solving the Einstein equations exactly yields an anisotropic energy-momentum tensor whose density is negative and decays as $r^{-2}$, thus violating the weak energy condition near the axis. Three notable features emerge: (i) axis-centred negative energy; (ii) unequal transverse stresses; (iii) a torsional momentum flux $T_{ϕz}ω^{3}/r$. We identify stable photon orbits and deflection angle, fully helical geodesics, and torsion-controlled wave optics modes, suggesting laboratory analogues in twisted liquid-crystal and photonic systems. The coupling between the torsion parameter $ω$ and other physical parameters leads to significant effects, altering the motion along the positive or negative $z$-axis. These results make the twisted helical metric a useful test bed for studying the interplay of curvature, torsion, and matter in both gravitational and condensed-matter contexts.

gr-qc↗

arXiv2025

Observable signatures of Black Holes with Hernquist Dark Matter Halo having a cloud of strings: From Geodesics to Shadow

We present a comprehensive theoretical investigation of a novel black hole (BH) spacetime: a Schwarzschild BH embedded in a Hernquist-type dark matter halo (HDMH) and surrounded by a cloud of cosmic strings (CSs) -- collectively termed the Schwarzschild-HDMH with CS (SHDMHCS) configuration. By analyzing the spacetime geometry, we explore how key parameters -- the core radius and halo density of the dark matter, along with the string tension -- affect the geodesic motion of both massless and massive particles. Our results reveal that the combined influence of HDMH and CSs modifies the effective potentials for null and timelike geodesics, leading to distinct dynamical behavior compared to standard Schwarzschild geometry. We perform a perturbative analysis for scalar (spin-0), electromagnetic (spin-1), and Dirac (spin-1/2) fields, deriving the associated effective potentials and showing how both the dark halo and CSs alter field propagation and potential barriers. The shadow of the BH is studied in detail: we derive analytical expressions for photon sphere and shadow radii, finding that CSs tend to enlarge the shadow, while HDMH properties tend to shrink it. The combined effects of these parameters significantly influence the shadow's shape and size, producing potentially observable signatures. Our results establish that the SHDMHCS configuration yields distinct observational imprints detectable by present and forthcoming astrophysical instruments. This framework provides new tools for probing exotic matter distributions via gravitational wave observations, orbital dynamics, and high-resolution black hole imaging, offering a pathway to distinguish such configurations from simpler BH models in realistic environments.

gr-qc↗

arXiv2025

AdS Black String in a Cosmic Web: Geodesics, Shadows, and Thermodynamics

In a recent article (Ref. \cite{AOP}), the authors obtained a static, cylindrically symmetric Anti-de Sitter (AdS) black string (BS) solutions, which are cylindrical generalizations of black holes (BHs), surrounded by a cloud of strings (CS) and the quintessence field (QF), and discussed its properties. In the present study, we present a comprehensive analysis of cylindrically symmetric AdS BSs surrounded by CS and QF. Our analysis yields several significant results. We demonstrate that the presence of CS (parameter $α$) and QF (parameters $c$ and $w$) reduces the radius of circular photon orbits (CPO) and BH shadow size, with measurements constrained by Event Horizon Telescope (EHT) observations of Sagittarius A*. We find that time-like particle orbits show increased energy with higher $α$ and $c$ values. We calculate that C-energy, representing gravitational energy within cylindrical radius, decreases with radial distance but exhibits distinct responses to CS and QF parameters. We observe that scalar perturbation potential increases $r$ for specific $α$ and $c$ values, indicating stronger field-spacetime interactions away from the BS. We determine that Hawking temperature increases linearly with Schwarzschild radius, with parameter-dependent behavior varying based on QF state parameter $w$. These results demonstrate how CS and QF significantly modify the geodesic, perturbative, and thermodynamic properties of AdS BS, with potential observational implications for gravitational lensing, accretion disk dynamics, and BH evaporation signatures in future astronomical observations.

gr-qc↗

arXiv2025

Fingerprints of Loop Quantum Gravity Black Holes with Quintessence Field

In this study, we investigate a static, spherically symmetric black hole (BH) within the framework of Loop Quantum Gravity (LQG) surrounded by quintessence field. Our comprehensive analysis shows that the interplay between quantum corrections and exotic matter produces unique spacetime features, most notably a triple-horizon structure for specific parameter combinations. We derive the metric function incorporating both LQG parameters ($α$, $B$) and quintessence parameters ($c$, $w$), analyzing its implications for horizon structure through embedding diagrams. We examine null and timelike geodesics, calculating photon spheres, effective potentials, and orbital dynamics. Our study demonstrates how quantum and quintessence parameters affect BH shadow size and shape, offering potential observational signatures. Through scalar perturbation analysis, we compute quasinormal modes (QNMs) frequencies, confirming the stability of these hybrid BHs while identifying distinctive spectral characteristics. Finally, using the Gauss-Bonnet (GB) theorem modified approach, we derive an analytical expression for gravitational deflection angles, showing a hierarchical structure of contributions from classical, quintessence, and quantum effects at different distance scales.

gr-qc↗

arXiv2025

Geodesics and scalar perturbations of deformed AdS-Schwarzschild black hole with a global monopole surrounded by a quintessence field

We conduct a comprehensive investigation of a deformed AdS-Schwarzschild black hole with a global monopole surrounded by a quintessence field. Our analysis focuses on the geodesic motion of both null and timelike particles, enabling precise determination of the photon sphere and quantification of forces acting on photon particles. We systematically examine how the deformation parameter, control parameter, global monopole parameter, and quintessence field parameter influence the energy, angular momentum, and angular velocities of test particles in circular orbits within the equatorial plane. Additionally, we derive and analyze the perturbative potentials for scalar and electromagnetic fields, demonstrating how these parameters modify their structural profiles. Through time-domain integration, we explore the evolution of scalar and electromagnetic perturbations, revealing distinct phases of transient behavior and quasinormal ringing. Finally, we investigate the emission rates of this black hole, establishing connections between its shadow radius and thermal characteristics. Our findings reveal that the global monopole parameter, deformation parameter and quintessence field enhance black hole stability by reducing emission rates, while the control parameter, which helps avoid central singularities, accelerates evaporation by increasing emission.

gr-qc↗

arXiv2025

Magnetized Letelier black hole in AdS spacetime

In this study, we investigate the motion of charged, neutral, and light-like particles in a magnetized black hole solution surrounded by a cloud of strings in an anti-de Sitter (AdS) background. This spacetime admits several well-known solutions as special cases, including the Letelier-AdS black hole, the Melvin spacetime, and the Schwarzschild-AdS black hole. We demonstrate that key parameters characterizing the geometry-such as the cloud of strings parameter, the magnetic field strength, and the AdS radius-significantly affect the trajectories of these particles. Our analysis shows that increasing the cloud of strings parameter weakens the gravitational influence, while the magnetic field introduces additional attractive components that can destabilize particle orbits. We examine the photon sphere and calculate the black hole shadow, showing that the shadow radius decreases with increasing magnetic field parameter but increases with the cloud of strings parameter. These findings provide potential observables for distinguishing between different black hole models in realistic astrophysical environments.

gr-qc↗

arXiv2025

Geometric and Thermodynamic Properties of Frolov Black Holes with Topological Defects

We investigated a modified Frolov black hole (BH) model that incorporates both a global monopole (GM) and a cosmic string (CS) to explore the interplay between non-singular BH regularization and topological defect effects. In our study, we derived a spacetime metric characterized by a regulated core through a length scale parameter $α$ and introduced additional modifications via the GM parameter $η$ and the CS parameter $a$, which collectively alter the horizon structure and causal geometry of the BH. We analyzed the thermodynamic properties by deriving expressions for the mass function, Hawking temperature, and entropy, and found that the inclusion of GM and CS significantly deviates the BH entropy from the conventional Bekenstein-Hawking area law, while numerical investigations showed that the shadow radius exhibits contrasting behaviors: the Frolov parameters tend to reduce the shadow size whereas the topological defects enhance it. Furthermore, we examined the dynamics of scalar and electromagnetic perturbations by solving the massless Klein-Gordon equation in the BH background and computed the quasinormal modes (QNMs) using the WKB approximation, which confirmed the BH's stability and revealed that the oscillation frequencies and damping rates are strongly dependent on the parameters $α$, $q$, $η$, and $a$. Our results suggest that the distinct observational signatures arising from this composite BH model may provide a promising avenue for testing modified gravity theories in the strong-field regime.

gr-qc↗

arXiv2025

Gravitational Lensing Phenomena of Ellis-Bronnikov-Morris-Thorne Wormhole with Global Monopole and Cosmic String

In this paper, we theoretically investigate gravitational lensing within the space-time framework of traversable wormholes, focusing on the combined effects of a global monopole and a cosmic string. Specifically, we examine the Ellis-Bronnikov-Morris-Thorne wormhole metric and analyze how these topological defects influence photon trajectories. By considering the weak-field limit, we derive analytical expressions for the photon deflection angle, highlighting how factors such as the wormhole throat radius, the global monopole charge, and the cosmic string influence the gravitational lensing phenomenon. We also examine the weak-field limit of lensing phenomena for a zero wormhole throat radius and derive an analytical expression for the deflection angle of photon light in this scenario.

gr-qc↗

arXiv2025

Ayón-Beato-García black hole in AdS space-time surrounded by quintessence: geodesic, shadow and thermodynamics

In this study, we present a novel exact solution to the gravitational field equations, known as the Ayón-Beato-García black hole solution, set against the backdrop of anti-de Sitter space and surrounded by a quintessence field. This solution serves as an interpolation between three distinct anti-de Sitter black hole configurations, namely, the Ayón-Beato-García, Schwarzschild-Kiselev, and the standard Schwarzschild black hole solutions. The first aspect of our investigation focuses on the geodesic motion of particles, where we explore how the black hole's space-time geometry-incorporating the effects of nonlinear electrodynamics, the quintessence field, and the curvature radius-influences the dynamics of both massless and massive particles near the black hole. To further enrich our analysis, we extend the study to include the perturbative dynamics of a massless scalar field within the black hole solution, placing special emphasis on the scalar perturbative potential. Subsequently, we focus into the phenomenon of black hole shadows, examining how various parameters, such as the nonlinear electrodynamics, the curvature of space-time and the presence of the quintessence field, impact the size and shape of the shadow cast by the black hole. In the final segment of our study, we shift our attention to the thermodynamics of the black hole solution. We compute several essential thermodynamic quantities, including the Hawking temperature, specific heat capacity, and Gibbs free energy, analyzing how these properties evolve in response to changes in the various parameters that define the space-time geometry, which in turn affect the gravitational field when compared to the traditional black hole

gr-qc↗

arXiv2025

Motions of Test Particles in Gravitational Field, Perturbations and Greybody Factor of Bardeen-like AdS Black Hole with Phantom Global Monopoles

We investigate the dynamics of test particles, perturbations, and greybody factors within the framework of a Bardeen-like AdS black hole (BH) with a phantom global monopole. This study explores the interactions between nonlinear electrodynamics, the energy scale of symmetry breaking, and space-time topology. We analyze the geodesic motion of null and time-like particles, deriving effective potentials that describe their trajectories. Utilizing the Regge-Wheeler potential, we calculate the quasinormal modes (QNMs) for scalar, vector, and tensor perturbations, applying the sixth-order WKB approximation. Our findings highlight how the Bardeen-like parameter ($\mathrm{b}$) and the energy scale of symmetry breaking, characterized by the parameter ($η$), influence the QNM spectra, with potential implications for gravitational wave observations. We also examine greybody factors, focusing on the transmission and reflection coefficients for scalar and axial fields, and employ semi-analytic techniques to derive precise bounds. Furthermore, we assess the thermodynamic stability of the BH, emphasizing the role of these parameters in phase transitions and stability criteria.

hep-th↗

arXiv2025

Rainbow gravity effects on quantum dynamics of scalar and oscillator fields in a topological defect cosmological space-time

In this paper, we investigate the quantum dynamics of scalar and oscillator fields in a topological defect space-time background under the influence of rainbow gravity's. The rainbow gravity's are introduced into the considered cosmological space-time geometry by replacing the temporal part $dt \to \frac{dt}{\mathcal{F}(χ)}$ and the spatial part $dx^i \to \frac{dx^i}{\mathcal{H} (χ)}$, where $\mathcal{F}, \mathcal{H}$ are the rainbow functions and $χ=E/E_p$. We derived the radial equation of the Klein-Gordon equation and its oscillator equation under rainbow gravity's in topological space-time. To obtain eigenvalue of the quantum systems under investigations, we set the rainbow functions $\mathcal{F}(χ)=1$ and $\mathcal{H}(χ)=\sqrt{1-β\,χ^p}$, where $p=1,2$. We solve the radial equations through special functions using these rainbow functions and analyze the results. In fact, it is shown that the presence of cosmological constant, the topological defect parameter $α$, and the rainbow parameter $β$ modified the energy spectrum of scalar and oscillator fields in comparison to the results obtained in flat space.

gr-qc↗