arXiv subjects

M. Azam

Publications and source records attributed to M. Azam.

At least 19 recordsLinked to original sources

arXiv2026

Quasinormal Modes, Greybody Factors and Rigorous Bounds for Quantum Oppenheimer-Snyder Black Hole with Quintessential Dark Energy and a String Clouds

We obtained quasinormal modes and greybody factors of the quantum Oppenheimer-Snyder (QOS) black hole with quintessential dark energy and string clouds. We compute the effective potentials of the scalar and the vector perturbation fields and analyze their graphical behavior. For this, we compute quasinormal mode frequencies of the QOS black hole, that is surrounded by quintessence dark energy and a cloud of strings and this is done by 6th-order Wentzel-Kramers-Brillouin (WKB) approximation method. We observe the quasinormal frequencies by analyzing both the quintessence parameters and the string cloud parameters. We also examine the GFs by analyzing the role of string cloud ($\tilde{a}_{e}$), quantum deformation ($\tilde{\sigma}_{e}$), and quintessence ($\tilde{h}_{e}$) parameters. It is found that GFs are significantly influenced by the parameters of $\tilde{a}_{e}$, $\tilde{\sigma}_{e}$, and $\tilde{h}_{e}$. In the case of scalar perturbation, we also give strict limits of the GFs and check the influence of the parameters of $\tilde{a}_{e}$, $\tilde{\sigma}_{e}$, and $\tilde{h}_{e}$.

gr-qc↗

arXiv2025

Study of Kiselev Black Hole in Quantum Fluctuation Modified Gravity via Quasinormal modes and Greybody Factors

In this work, we formulate the wave function to compute the effective potential of scalar and vector fields for the Kiselve black hole in the background of quantum fluctuation modified gravity. Using the 6th-order Wentzel-Kramers-Brillouin approach, the quasinormal modes for the considered black hole are obtained through scalar and vector perturbation fields. We investigate the quasinormal frequency by considering several values of the metric and equation of state ($\mho$ and $\bar{\bar{\omega}}$) parameter, respectively. The real part values of the quasinormal modes drop as the $\mho$ values rise. Later, the greybody factors of the black hole are determined and found that the parameters $\mho$, $\bar{\bar{\omega}}$ and the multipole moment $l$ significantly affects the greybody factors. Additionally, for scalar perturbations, we graphically analyze the rigorous bound of the greybody factor under the effects of parameters $\mho$ and $l$.

gr-qc↗

arXiv2025

Anisotropic Compact Star with Vaidya-Tikekar Potential in $f(Q)$ Gravity

The goal of this work is to develop physical models for spherically symmetric systems in the realm of $f(Q)$ gravity. The field equations are set up for anisotropic fluid and formulate these equations using physical ansatz of Vaidya-Tikekar solution. The intrinsic constants of the model be ascertained by matching the interior solution to the external Schwarzschild solution. The use of accessibility conditions helps to understand the physical viability of the obtained model. LMC X-4 pulsar is used as a toy model to test the viability of the model and Mathematica software is used for deeper insights and visualization of the physical parameters against fixed values of constants.

gr-qc↗

arXiv2025

Rotating Einstein-Maxwell-Dilaton Black Hole as a Particle Accelerator

Similar to particle accelerators, black holes also have the ability to accelerate particles, generating significant amounts of energy through particle collisions. In this study, we examine the horizon and spacetime structures of a rotating black hole within the framework of Einstein-Maxwell-Dilaton gravity. Additionally, we extend the analysis to explore particle collisions and energy extraction near this black hole using the Banados-Silk-West mechanism. Our findings reveal that the mass and angular momentum of the colliding particles significantly influence the center of mass energy, more so than the parameters of the black hole itself. Furthermore, we apply the Banados-Silk-West mechanism to massless particles, particularly photons, while disregarding their intrinsic spin in plasma; an aspect that has not been previously explored. The Banados-Silk-West mechanism cannot be directly applied, as the refractive index condition only permits photon propagation, meaning that massive particles in vacuum cannot be included in this study. We derive the propagation conditions for photons and analyze photon collisions by treating them as massive particles in a dispersive medium. The impact of the plasma parameter on the extracted center of mass energy is also examined. Our results show that the plasma parameter has a relatively weak and unchanged effect on the center of mass energy across all cases, indicating that energy losses due to friction within the medium are a contributing factor.

gr-qc↗

arXiv2023

Relativistic Polytropic Models of Charged Anisotropic Compact Object

In this paper, we have introduced new viable solutions of Einstein-Maxwell field equations by incorporating the features of anisotropic matter distribution in the realm of General theory of Relativity ($GR$). For this procurement, we have employed a Finch-Skea spacetime along with a generalized polytropic equation of state ($EoS$). We have constructed various models of generalized polytropes by assuming the different choices of the polytropic index i.e.,$\eta=\frac{1}{2}, \frac{2}{3}, 1$ and $2$. The numerous physical characteristics of these considered models have been studied via graphical analysis, which obey all the essential conditions of the astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models can be regained to the various cases such as linear, quadratic and polytropic $EoS$.

gr-qc↗

arXiv2016

Cracking of Charged Polytropes with Generalized Polytropic Equation of State

We discuss the occurrence of cracking in charged anisotropic polytropes with generalized polytropic equation of state through two different assumptions; (i) by carrying out local density perturbations under conformally flat condition (ii) by perturbing anisotropy, polytropic index and charge parameters. For this purpose, we consider two different definitions of polytropes exist in literature. We conclude that under local density perturbations scheme cracking does not appears in both types of polytropes and stable configuration are observed, while with second kind of perturbation cracking appears in both types of polytropes under certain conditions.

physics.gen-ph↗

arXiv2016

On Cracking of Charged Anisotropic Polytropes

Recently in \cite{34}, the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways $(i)$ by perturbing polytropic constant, anisotropy and charge parameter $(ii)$ by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to \cite{33} in the absence of charge.

physics.gen-ph↗

arXiv2016

Charged Cylindrical Polytropes with Generalized Polytropic Equation of State

We study the general formalism of polytropes in relativistic regime with generalized polytropic equations of state in the vicinity of cylindrical symmetry. We take charged anisotropic fluid distribution of matter with conformally flat condition for the development of general framework of polytropes. We discussed the stability of the model by Whittaker formula and concluded that one of the developed model is physically viable.

physics.gen-ph↗

arXiv2016

Born-Infeld Thin-shell Wormholes Supported by Generalized Cosmic Chaplygin Gas

This paper investigates thin-shell wormholes in Born-Infeld theory supported by generalized Cosmic Chaplygin gas (GCCG). We study their stability via radial perturbations for distinct values of charge and Born-Infeld parameter. The comparison of wormhole solutions corresponding to generalized Chaplygin gas, modified Chaplygin gas with GCCG quation of state is established. It is found that similar type of wormhole solutions exists for small value of charge and Born-Infeld parameter for all type of equation of state, while some extra stable as well as unstable solution are found corresponding to large value of charge and Born-Infeld parameter. Thus, it is concluded that GCCG and large value of charge may responsible for such extra solutions.

physics.gen-ph↗

arXiv2016

Study of polytropes with Generalized polytropic Equation of State

The aim of this paper is to discuss the theory of Newtonian and relativistic polytropes with generalized polytropic equation of state. For this purpose, we formulated the general framework to discuss the physical properties of polytrops with anisotropic inner fluid distribution under conformally flat condition in the presence of charge. We investigate the stability of these polytrops in the vicinity of generalized polytropic equation through Tolman-mass. It is concluded that one of the derived models is physically acceptable.

physics.gen-ph↗

arXiv2015

Fate of Electromagnetic Field on the Cracking of PSR J1614-2230 in Quadratic Regime

In this paper, we study the cracking of compact object PSR J1614-2230 in quadratic regime with electromagnetic field. For this purpose, we develop a general formalism to determine the cracking of charged compact objects. We apply the local density perturbations to the hydrostatic equilibrium equation as well as all the physical variables involve in the model. We plot the force distribution function against radius of the star with different values of model parameters both with and without charge. It is found that PSR J1614-2230 remains stable (no cracking) corresponding to different values of parameters when charge is zero, while it exhibit cracking (unstable) when charge is introduced. We conclude that stability region increases as amount of charge increases.

gr-qc↗

arXiv2013

The Stability of a Shearing Viscous Star with Electromagnetic Field

We analyze the role of electromagnetic field for the stability of shearing viscous star with spherical symmetry. Matching conditions are given for the interior and exterior metrics. We use perturbation scheme to construct the collapse equation. The range of instability is explored in Newtonian and post Newtonian (pN) limits. We conclude that the electromagnetic field diminishes the effects of shearing viscosity in the instability range and makes the system more unstable at both Newtonian and post Newtonian approximations.

gr-qc↗

arXiv2013

Spherical Thin-Shell Wormholes and Modified Chaplygin Gas

The purpose of this paper is to construct spherical thin-shell wormhole solutions through cut and paste technique and investigate the stability of these solutions in the vicinity of modified Chaplygin gas. The Darmois-Israel formalism is used to formulate the stresses of the surface concentrating the exotic matter. We explore the stability of the wormhole solutions by using the standard potential method. We conclude that there exist more stable as well as unstable solutions than the previous study with generalized Chaplygin gas \cite{15}.

gr-qc↗

arXiv2013

Mechanical Stability of Cylindrical Thin-Shell Wormholes

In this paper, we apply the cut and paste procedure to charged black string for the construction of thin-shell wormhole. We consider the Darmois-Israel formalism to determine the surface stresses of the shell. We take Chaplygin gas to deal with the matter distribution on shell. The radial perturbation approach (preserving the symmetry) is used to investigate the stability of static solutions. We conclude that stable static solutions exist both for uncharged and charged black string thin-shell wormholes for particular values of the parameters.

gr-qc↗

arXiv2013

Stability of Thin-Shell Wormholes in Nonlinear Electrodynamics

In this paper, we construct thin-shell wormholes by applying the cut and paste procedure to a regular charged black hole in nonlinear electrodynamics field. We discuss different physical aspects of wormholes such as, the possible equation of state to matter shell, attractive or repulsive nature of wormhole and total amount of exotic matter required. The thin-shell equation of motion with and without cosmological constant is also investigated under linearized perturbation. Finally, we explore the stability regions interpreted by the parameter $\beta$ (speed of sound) and conclude that there are realistic stability regions for some fixed values of parameters.

gr-qc↗

arXiv2013

Effects of Electromagnetic Field on the Dynamical Instability of Expansionfree Gravitational Collapse

In this paper, we discuss the effects of electromagnetic field on the dynamical instability of a spherically symmetric expansionfree gravitational collapse. Darmois junction conditions are formulated by matching interior spherically symmetric spacetime to exterior Reissner-Nordstr$\ddot{o}$m spacetime. We investigate the role of different terms in the dynamical equation at Newtonian and post Newtonian regimes by using perturbation scheme. It is concluded that instability range depends upon pressure anisotropy, radial profile of energy density and electromagnetic field, but not on the adiabatic index $\Gamma$. In particular, the electromagnetic field reduces the unstable region.

gr-qc↗

arXiv2013

Stability of Anisotropic Cylinder with Zero Expansion

We study the dynamical instability of anisotropic collapsing cylinder with the expansion-free condition, which generates vacuum cavity within fluid distribution. The perturbation scheme is applied to distinguish Newtonian, post-Newtonian and post-post Newtonian terms, which are used for constructing dynamical equation at Newtonian and post-Newtonian regimes. We analyze the role of pressure anisotropy and energy density inhomogeneity on the stability of collapsing cylinder. It turns out that stability of the cylinder depends upon these physical properties of the fluid, not on the stiffness of the fluid.

gr-qc↗

arXiv2013

Stability Analysis of Thin-Shell Wormholes from Charged Black String

In this paper, we construct thin-shell wormholes from charged black string through cut and paste procedure and investigate its stability. We assume modified generalized Chaplygin gas as a dark energy fluid (exotic matter) present in the thin layer of matter-shell. The stability of these constructed thin-shell wormholes is investigated in the scenario of linear perturbations. We conclude that static stable as well as unstable configurations are possible for cylindrical thin-shell wormholes.

gr-qc↗