arXiv subjects

Faizuddin Ahmed

Publications and source records attributed to Faizuddin Ahmed.

At least 109 records · Page 6Linked to original sources

arXiv2025

Shadow properties and orbital dynamics around an effective quantum-modified black hole surrounded by quintessential dark energy

In this study, we investigate black holes (BHs) surrounded by a quintessence field (QF) within the framework of effective quantum gravity (EQG). We analyze the spacetime metric characterized by quantum correction parameter $ξ$ and quintessence parameters $(c,w)$, revealing a rich three-horizon structure whose properties depend on both quantum effects and dark energy. Our main focus is on understanding the observational signatures and dynamical behavior of these modified BHs. We derive analytical expressions for the photon sphere and shadow radius for various values of the state parameter, finding that quintessence fields increase the shadow radius while quantum corrections decrease it-a distinctive interplay that creates potentially observable effects. Using Event Horizon Telescope data from M87*, we establish constraints on the quantum correction parameter, showing that the allowable range for $ξ$ increases with the quintessence parameter $c$. We conduct a comprehensive analysis of null and timelike geodesics, demonstrating how quantum corrections enhance interactions between photons and the gravitational field while modifying the energy, angular momentum, and stability properties of massive particle orbits. Our investigation extends to periodic orbits characterized by zoom-whirl behavior, finding that quintessence allows such orbits to occur at lower energies compared to purely quantum-corrected BHs. We further analyze scalar perturbations and their effective potentials, which reveal how both quantum and quintessence effects shape the response characteristics of these BHs. Throughout our study, we find that quantum corrections and quintessence frequently produce counteracting effects on observables that could provide simultaneous tests of quantum gravity theories and dark energy models through future high-precision astronomical observations.

gr-qc↗

arXiv2025

Photon spheres, gravitational lensing/mirroring, and greybody radiation in deformed AdS-Schwarzschild black holes with phantom global monopole

In this study, we investigate the geodesic structure, gravitational lensing/mirroring phenomena, and scalar perturbations of deformed AdS-Schwarzschild black holes with global monopoles, incorporating both ordinary and phantom configurations. We introduce a modified black hole metric characterized by a deformation parameter $α$, a control parameter $β$, and a symmetry-breaking scale parameter $η$, which collectively influence the spacetime geometry. Through comprehensive geodesic analysis, we determine the photon sphere radius numerically for various parameter configurations, revealing significant differences between ordinary and phantom global monopoles. The stability of timelike circular orbits is assessed via the Lyapunov exponent, demonstrating how these parameters affect orbital dynamics. Our gravitational lensing analysis, employing the Gauss-Bonnet theorem, reveals a remarkable gravitational mirroring effect in phantom monopole spacetimes at high AdS curvature radii, where light rays experience negative deflection angles-being repelled rather than attracted by the gravitational field. Furthermore, we analyze massless scalar perturbations and derive the corresponding greybody factors, which characterize the transmission of Hawking radiation through the effective potential barrier surrounding the black hole. Our numerical results indicate that phantom global monopoles substantially modify both gravitational lensing/mirroring properties and the radiation spectrum compared to ordinary monopoles. The presence of the deformation parameter $α$ introduces additional complexity to the system, leading to distinct thermodynamic behavior that deviates significantly from the standard AdS-Schwarzschild solution.

gr-qc↗

arXiv2025

Cylindrical black hole solutions in $f(\mathcal{R})$ and $f(\mathcal{R},\mathcal{A},A^{μν}A_{μν})$ modified gravity

We explore a cylindrical black hole (BH) space-time introduced by Lemos, in the context of modified gravity theories. Specifically, we focus on $f(\mathcal{R})$-gravity framework, where we choose two form functions, $f(\mathcal{R})=(\mathcal{R}+α_1\,\mathcal{R}^2+α_2\,\mathcal{R}^3+α_3\,\mathcal{R}^4+α_4\,\mathcal{R}^5)$ and $f(\mathcal{R})=\mathcal{R}+α_k\,\mathcal{R}^{k+1},\quad (k=1,2,...n)$. We solve the modified field equations incorporating zero energy-momentum tensor, $\mathcal{T}^{μν}=0$ and obtain the result. Moreover, we study another well-known modified gravity theory called Ricci-Inverse ($\mathcal{RI}$) gravity and investigate this Lemos black hole (LBH) space-time. To achieve this, we consider different classes of models defined as follows: (i) Class-\textbf{I} model: $f(\mathcal{R}, \mathcal{A})=(\mathcal{R}+β\,\mathcal{A})$, (ii) Class-\textbf{II} model: $f(\mathcal{R}, A^{μν}\,A_{μν})=(\mathcal{R}+γ\,A^{μν}\,A_{μν})$, and (iii) Class-\textbf{III} model: $f(\mathcal{R}, \mathcal{A}, A^{μν}\,A_{μν})=(\mathcal{R}+α_1\,\mathcal{R}^2+α_2\,\mathcal{R}^3+β_1\,\mathcal{A}+β_2\,\mathcal{A}^2+γ\,A^{μν}\,A_{μν})$, where $\mathcal{A}=g_{μν}\,A^{μν}$ is the anti-curvature scalar, $A^{μν}$ is the anti-curvature tensor, the reciprocal of the Ricci tensor $R_{μν}$. We solve the modified field equations under the same aforementioned scenario of energy-momentum tensor, and obtain the result. Subsequently, we study the geodesic motions of test particles around this LBH within the Ricci-Inverse and $f(\mathcal{R})$-gravity theories and analyze the outcomes. We demonstrate that different coupling constants chosen in these modified gravity theories influences the usual cosmological constant $Λ$, and thus, shifted the result in comparison to the general relativity case.

gr-qc↗

arXiv2025

Fermionic fields in a four-dimensional Bonnor-Melvin-Lambda space-time

In this paper, we investigate how the gravitational field generated by a four-dimensional electrovacuum cosmological space-time influences the dynamics of fermionic fields governed by the Dirac equation, while also considering the effects of topology. We derive the radial wave equation corresponding to the relativistic Dirac equation and subsequently obtain analytical solutions for the energy levels and wave functions of the fermionic field within our chosen framework. Our analysis reveals that various parameters, including geometric topology, the cosmological constant, and quantum numbers, play significant roles in determining the eigenvalue solution of the quantum particles. Specifically, we demonstrate that the presence of the topological parameter disrupts the degeneracy of the energy spectrum.

gr-qc↗

arXiv2025

A new black hole coupled with nonlinear electrodynamics surrounded by quintessence: Thermodynamics, Geodesics, and Regge-Wheeler Potential

We present a new exact solution to the gravitational field equations, where nonlinear electrodynamics (NLED) serves as the matter source in the presence of a quintessence field (QF). This solution describes a static, spherically symmetric black hole in the context of Anti-de Sitter (AdS) space, with the black hole (BH) surrounded by quintessence matter. The resulting black hole solution generalizes the AdS Schwarzschild-Kiselev black hole and reduces to the standard AdS-Schwarzschild black hole in the appropriate limits. Additionally, under certain conditions, this solution recovers the Bardeen-Kiselev regular black hole. We further explore the horizon structure and thermodynamic properties of this new black hole spacetime, accounting for the contributions from both NLED and the QF, including the state parameter of the QF. These contributions modify the spacetime geometry, thereby altering the thermodynamic behavior of the black hole. Moreover, we analyze the geodesic equations and show how NLED and the QF influence the effective potential for massless photon particles. Finally, we study the Regge-Wheeler (RW) potential for this regular black hole and demonstrate how variations in the parameters (NLED and QF) affect the RW potential for fields of different spins: spin-zero ($S=0$), spin-one ($S=1$), and spin-two ($S=2$). To illustrate the effects, we provide graphical representations of the RW potential for both multipole numbers $\ell=0$ and $\ell=1$.

gr-qc↗

arXiv2025

Dynamics of test particles and scalar perturbations around Ayón-Beato-García black hole coupled with cloud of strings

In this paper, we investigate the geodesic motion and scalar perturbations of the Ayón-Beato-García (ABG) black hole (BH) coupled with a cloud of strings (CS). By employing the effective potential approach, we analyze the trajectories of massless and massive test particles around this regular BH solution. The interplay between nonlinear electrodynamics (NLED) and CS significantly modifies the spacetime geometry, resulting in distinct dynamical properties for test particles. The behavior of null and timelike geodesics, including their stability and escape conditions, is thoroughly examined. In addition to the geodesic analysis, we study scalar perturbations by deriving the Klein-Gordon equation for massless scalar fields in this spacetime. The resulting Schrödinger-like wave equation reveals an effective potential that depends intricately on the NLED and CS parameters. Furthermore, we compute the greybody factors (GFs) to explore the energy transmission and absorption properties of theBH. Our results demonstrate that the NLED parameter $g$ and the CS parameter $α$ play pivotal roles in modulating the GFs, influencing the energy spectrum of scalar radiation. These results provide significant understanding of the observational characteristics of the ABG NLED-CS BH in astrophysical contexts.

gr-qc↗

arXiv2024

Scalar, Vector Perturbations and Effective Hawking Radiation of Cylindrical Black Holes in $f(\mathcal{R})$ and Ricci-Inverse Gravity

This paper investigates scalar perturbations and quasinormal modes (QNMs) associated with cylindrical black holes constructed within the frameworks of $f(\mathcal{R})$-gravity and Ricci-Inverse ($\mathcal{RI}$) gravity. Moreover, we study the modified Hawking radiation in these black hole solutions and analyze the effects of coupling constants. These modified theories, which extend general relativity by introducing higher-order curvature corrections and additional geometric terms, provide a rich platform for exploring deviations from standard gravitational physics. The study begins by revisiting the cylindrical black holes in these modified gravity theories, where the effective cosmological constants respectively, are represented by $Λ_m^{f(\mathcal{R})}$ and $Λ_m^{\mathcal{RI}}$ related to the coupling constants unique to each framework. Afterwards, the QNMs, intrinsic damped oscillations of the black hole space-time, are analyzed to probe the stability of the system, with the effective potential $V$ revealing the impact of the modified gravity parameters. Additionally, the thermodynamic properties of the black holes are examined through the lens of the Generalized Uncertainty Principle (GUP), which introduces quantum corrections to Hawking radiation. The GUP-modified Hawking temperature and entropy are derived, demonstrating significant deviations from classical results and highlighting the quantum gravitational effects in these modified frameworks. By linking QNMs, thermodynamics, and quantum corrections, this work not only deepens the understanding of modified gravity theories but also offers potential observational pathways to test their validity.

gr-qc↗

arXiv2024

Spin-dependent Regge-Wheeler Potential and QNMs in Quantum Corrected AdS Black Hole with Phantom Global Monopoles

In this paper, we investigate the geodesic motion of test particles in the spacetime surrounding a static, spherically symmetric black hole, which is described by an AdS-Schwarzschild-like metric and incorporates a quantum correction. This black hole also features phantom global monopoles, which modify the structure of the black hole space-time. We begin by deriving the effective potential governing the motion of test particles in this system and carefully analyze the impact of quantum correction in the presence of both phantom and ordinary global monopoles. Furthermore, we extend our study to include the spin-dependent Regge-Wheeler (RW) potential, which characterizes the dynamics of perturbations in this quantum-corrected black hole background. By examining this RW potential for various spin fields, we show how quantum corrections affect its form in the presence of both phantom and ordinary global monopoles. Our analysis demonstrate that quantum correction significantly alter the nature of the RW-potential, influencing the stability, and behavior of test particles and perturbations around the black hole.

gr-qc↗

arXiv2024

Stationary BTZ space-time in Ricci-Inverse and $f(\mathcal{R})$ gravity theories

In this paper, we explore a stationary BTZ space-time within the framework of modified gravity theory, specifically focusing on Ricci-inverse gravity. It is important to clarify that ``Ricci-inverse" refers to the inverse of the Ricci tensor, not the Ricci scalar. We consider a general class of this gravity theory, where the function $f$ is defined by $f(\mathcal{R}, \mathcal{A}, A^{μν}\,A_{μν})$, with $\mathcal{R}$ and $\mathcal{A}$ representing the Ricci and anti-curvature scalars, respectively and $A^{μν}$ is the anti-curvature tensor. We demonstrate that stationary BTZ space-time is a valid solution in this gravity theory, wherein the cosmological constant undergoes modifications due to the coupling constants. Moreover, we study another modified gravity theory known as $f(\mathcal{R})$-gravity and analyze the stationary BTZ space-time. Subsequently, we fully integrate the geodesic equations for BTZ space-time constructed within the Ricci-Inverse gravity, expressing the solutions in terms of elementary functions and compared with the GR result. We classify different types of geodesics, including null and time-like geodesics, under three conditions: (i) nonzero mass and angular momentum, $M \neq 0, J\neq 0$, (ii) massless BTZ space-time, $M=0$ and $J=0$, and (iii) $M=-1, J=0$, that is $AdS_3$-type, and analyze the results in modified gravity theories and compare with the general relativity case.

gr-qc↗

arXiv2024

Quasinormal Modes and GUP-Corrected Hawking Radiation of BTZ Black Holes within Modified Gravity Frameworks

This paper aims to explore the quasinormal modes (QNMs) and effective potential profiles of massless and rotating BTZ black holes within the frameworks of $f(\mathcal{R})$ and Ricci-Inverse ($\mathcal{RI}$) modified gravity theories, which, while producing similar space-time structures, exhibit variations due to distinct cosmological constants, $Λ_m$. We derive wave equations for these black hole perturbations and analyze the behavior of the effective potential $V_{\text{eff}}(r)$ under different values of mass $m$, cosmological constant $Λ_m$, and modified gravity parameters $α_1$, $α_2$, $β_1$, $β_2$, and $γ$. The findings indicate that increasing mass and parameter values results in a raised potential barrier, implying stronger confinement of perturbations and impacting black hole stability. Incorporating the generalized uncertainty principle, we also study its effect on the thermodynamics of rotating BTZ black holes, demonstrating how GUP modifies black hole radiation, potentially observable in QNM decay rates. Additionally, we investigate the motion of particles through null and timelike geodesics in static BTZ space-time, observing asymptotic behaviors for null geodesics and parameter-dependent shifts in potential for timelike paths. The study concludes that modified gravity parameters significantly influence QNM frequencies and effective potential profiles, offering insights into black hole stability and suggesting that these theoretical predictions may be tested through gravitational wave observations.

gr-qc↗

arXiv2024

A five-dimensional vacuum-defect wormhole space-time

In this study, we present a novel extension to the Klinkhamer vacuum-defect model by incorporating a fifth spatial dimension. This modification results in the formulation of a comprehensive five-dimensional wormhole space-time. Crucially, this extension preserves its classification as a vacuum solution to the field equations, thereby automatically satisfying all energy conditions. We demonstrate that this five-dimensional vacuum-defect space-time can be expressed in a pure canonical form, and thus, locally reduces to five-dimensional Minkowski space. Finally, we explore the geodesic equations in the vicinity of this five-dimensional vacuum-defect wormhole, offering insights into its intriguing properties.

gr-qc↗

arXiv2024

Effects of gravity rainbow on scalar bosonic and oscillator fields in Bonnor-Melvin space-time with a cosmological constant

In this paper, we explore the relativistic quantum motion of spin-zero scalar charge-free particles influenced by rainbow gravity's (RG's) in Bonnor-Melvin magnetic space-time, a four-dimensional solution featuring a positive cosmological constant. We solve the Klein-Gordon equation in this scenario by using two sets of rainbow function: (i) $f(χ)=\frac{1}{(1-β\,χ)}$,\,\, $h(χ)=1$ and (ii) $f(χ)=\frac{1}{(1-β\,χ)}=h(χ)$, where $0 < χ\left(=\frac{|E|}{E_p}\right) \leq 1$ with $E_p$ being the Planck's energy, $E$ is the particle's energy, and $β$ is the rainbow parameter. Furthermore, we study the relativistic quantum oscillator through the Klein-Gordon oscillator equation in the same Bonnor-Melvin magnetic space-time under RG effects. Employing the first pair of rainbow function, we obtain an approximate eigenvalue solution of the quantum oscillator fields. Notably, we demonstrate that the relativistic energy profile of scalar and oscillator particles are influenced by the topology of the geometry and the cosmological constant which is related with the magnetic field strength lies along the symmetry axis. Additionally, we see the impact of rainbow parameter on these approximate relativistic energy profiles in both quantum systems.

gr-qc↗

arXiv2024

Morris-Thorne-type wormhole with global monopole charge and the energy conditions

In this paper, we investigate Morris-Thorne-type wormholes with global monopole charge using various shape function forms known in the literature. We solve the Einstein field equations incorporating an anisotropic energy-momentum tensor and obtain different physical quantities associated with the matter-content. A crucial aspect of this study is the non-exotic matter distribution, examined through the evaluation of energy conditions, and exploring how different shape functions impact these conditions. Additionally, the anisotropy parameter is calculated to quantify the extent of attractive or repulsive behavior. Our study demonstrates that for different types of shape function forms, the energy conditions are influenced by the global monopole parameter. Our findings provide valuable insights for further theoretical explorations of these fascinating hypothetical structures in the realm of general relativity and beyond.

gr-qc↗

arXiv2024

Gravitational lensing in holonomy corrected spherically symmetric black holes with phantom global monopoles

In this paper, we address a theoretical investigation of the gravitational lensing phenomenon within the space-time framework of a holonomy-corrected spherically symmetric black hole (BH), incorporating both ordinary and phantom global monopoles. Our focus lies on the analysis of null geodesics within this black hole background, examining the influence of ordinary and phantom global monopoles on the effective potential of null geodesics of the system. Afterwards, we derive analytical expressions for the deflection angle of photon light, considering weak field limit. The obtain expressions are presented up to the second order of the Loop Quantum Gravity parameter, enabling a thorough examination of the impact of ordinary and phantom global monopoles on the deflection angle.

gr-qc↗

arXiv2024

Higher-dimensional topologically charged traversable defect wormhole with non-exotic matter

In this study, we explore a topologically charged higher-dimensional traversable defect wormhole, with a specific emphasis on five dimensions. Particularly noteworthy is the fact that the matter-energy distribution attributed to this charged wormhole configuration adheres to the weak energy condition, thus presenting an instance of a five-dimensional wormhole supported by non-exotic matter. Furthermore, our analysis shows that scalar quantities related to space-time curvature and parameters associated with the matter-energy distribution remain finite at the wormhole throat. Moreover, they diminish as distance extends toward infinity, indicating the asymptotic flatness inherent in our model.

gr-qc↗

arXiv2024

Harmonic oscillator system in topologically charged Eddington-inspired Born-Infeld gravity space-time and Wu-Yang magnetic monopole

We investigate the quantum dynamics of a harmonic oscillator (HO) system within the framework of topologically charged Eddington-inspired Born-Infeld (EiBI) gravity space-time. Additionally, we incorporate the Wu-Yang magnetic monopole (WYMM) into the quantum system and analyze the influences of modified gravity, the topological charge, and WYMM on this HO quantum mechanical system. Using analytical methods, we derive the energy eigenvalues and the corresponding eigenfunctions of the HO. Moreover, we consider a scenario where the EiBI-gravity parameter is absent and introduce an inverse square potential, including the WYMM, into the HO system. Our findings show significant deviations in the behavior of the HO system compared to the traditional quantum mechanical HO model, including alterations in the bound-state spectra and eigenfunctions. These results provide valuable insights into the interplay between quantum mechanical problems and alternative gravitational theories.

gr-qc↗

arXiv2024

PDM relativistic quantum oscillator in Einstein-Maxwell-Lambda space-time

In this analysis, we study the dynamics of quantum oscillator fields within the context of a position-dependent mass (PDM) system situated in an Einstein-Maxwell space-time, incorporating a non-zero cosmological constant. The magnetic field is aligned along the symmetry axis direction. To analyze PDM quantum oscillator fields, we introduce a modification to the Klein-Gordon equation by substituting the four-momentum vector $p_μ \to \Big(p_μ+i\,η\,X_μ+i\,\mathcal{F}_μ\Big)$ into the Klein-Gordon equation, where the four-vector is defibed by $X_μ=(0, r, 0, 0)$, $\mathcal{F}_μ=(0, \mathcal{F}_r, 0, 0)$ with $\mathcal{F}_r=\frac{f'(r)}{4\,f(r)}$, and $η$ is the mass oscillator frequency. The radial wave equation for the relativistic modified Klein-Gordon equation is derived and subsequently solved for two distinct cases: (i) $f(r)=e^{\frac{1}{2}\,α\,r^2}$, and (ii) $f(r)=r^β$, where $α\geq 0, β\geq 0$. The resultant energy levels and wave functions for quantum oscillator fields are demonstrated to be influenced by both the cosmological constant and the geometrical topology parameter which breaks the degeneracy of the energy spectrum. Furthermore, we observed noteworthy modifications in the energy levels and wave functions when compared to the results derived in the flat space background.

gr-qc↗

arXiv2024

Effects of external field and potential on non-relativistic quantum particles in disclinations background

In this work, we investigate the behavior of non-relativistic quantum particles immersed in a cosmic string space-time background. Our study involves the examination of these particles as they interact with a range of influences, including potential, magnetic, and quantum flux fields. We employ analytical methods to solve the associated wave equation, leading to the derivation of eigenvalue solutions for this quantum system. Subsequently, we leverage these eigenvalue solutions to scrutinize several potential models. For each model, we present and engage in a thorough discussion of the corresponding eigenvalue solutions. In an extension of our investigation, we explore the thermodynamic and magnetic properties of the quantum system when it is exposed to non-zero temperature conditions, denoted by $T \neq 0$. Our analysis encompasses the calculation of essential parameters such as the partition function for the system and other pertinent functions. Following these calculations, we meticulously examine and interpret the outcomes, shedding light on the system's behavior and characteristics in the presence of temperature variations. Furthermore, we calculate entropic information to investigate the location of particles in the system.

quant-ph↗