arXiv subjects

Adnan Malik

Publications and source records attributed to Adnan Malik.

18 recordsLinked to original sources

arXiv2026

Charged Anisotropic Compact Stars in $f(R,\phi,X)$ Gravity: A Class I Embedding Approach with Reissner-Nordstr\"{o}m Exterior

This work examines the physical characteristics of charged, anisotropic compact spheres within the framework of $f(R,\phi,X)$ modified gravity. Starting from a static, spherically symmetric spacetime, we employ an Adler-type ansatz for the temporal metric component $g_{tt}$. The corresponding radial metric component $g_{rr}$ is then systematically derived through application of the Karmarkar condition, which ensures a class-one embedding for the interior geometry. A crucial aspect of our approach involves matching the interior solution at the stellar boundary to the exterior Reissner--Nordstr$\ddot{0}$m spacetime---the established vacuum solution for charged, non-rotating masses. This matching procedure is essential for determining integration constants and verifying global physical consistency. Our comprehensive analysis of the resulting stellar model investigates multiple physical aspects, including energy density, radial and tangential pressures, anisotropy, equation-of-state parameters, energy conditions, mass function, compactness, and surface redshift. Stability assessment further incorporates examination of the adiabatic index and the Tolman--Oppenheimer--Volkoff equation. Collectively, our findings demonstrate that the charged compact star model presented here constitutes a physically viable configuration---free of singularities and maintaining stable equilibrium across the considered parameter space.

physics.gen-ph↗

arXiv2026

Topologically Charged Morris-Thorne-type Wormholes and the Energy Conditions

In this paper, we investigate topologically charged Morris-Thorne-type traversable wormholes by solving the Einstein field equations with an anisotropic fluid as the energy-momentum tensor and analysing the resulting solutions. In continuation to the earlier work (Eur. Phys. J C {\bf 84} (2024) 1037), we consider the shape functions such as: (i) $A(r)=r_0\,e^{r_0-r}$; (ii) $A(r)=r_0\,a^r/a^{r_0}$,\quad $0 < a<1$; (iii) $A(r)=r_0\,\left(\frac{\cosh r_0}{\cosh r}\right)^{\delta}$,\quad $\delta \geq 1$; (iv) $A(r)=\frac{1}{r}+\ln\!\frac{r}{r_0}$; (v) $A(r)=B\,r^n+(1-B)$; (vi) $A(r)=r_0\,\frac{\mbox{ln} (1+r)}{\mbox{ln} (1+r_0)}$, (vii) $A(r)=r_0+a\,r_0\,\left[\left(\frac{r}{r_0}\right)^\beta-1\right]$, where $\beta<1$ and $0 < a\,\beta <1$. We examine the energy conditions-namely, null, weak, strong, and dominant energy conditions and explore how topological charge influences or controls these conditions. Additionally, we calculate the anisotropy parameter to determine whether the wormhole geometry exhibits attractive or repulsive behavior. Our analysis demonstrates that the energy density of the anisotropic fluid is always positive. However, while some of the energy conditions are partially satisfied, others are violated.

gr-qc↗

arXiv2026

Odd-parity perturbations of trace-quadratic $f(R,T)$ black holes with anisotropic matter: admissible branches, axial ringdown, and a coupled-PINN benchmark

We study odd-parity gravitational perturbations of static black holes in trace-quadratic $f(R,T)=R+\alpha T^2$ gravity supported by an anisotropic effective fluid with constant closure parameters $(w_r,w_t)$. From the unreduced axial system and its principal symbol, we identify the sector of parameter space that supports a regular horizon, asymptotic flatness, and hyperbolic odd-sector evolution. Within this closure the admissible branch lies at negative $w_r$, while the commonly used positive-$w_r$ family fails the background regularity test and is kept only as a numerical comparison branch. On static admissible backgrounds the odd sector is exactly equivalent to Einstein gravity coupled to a frozen effective anisotropic fluid, so the physical axial spectrum is governed by a single gauge-invariant master equation. For the anchored branch $(w_r,w_t)=(-0.2,0.15)$ we compute the fundamental axial $\ell=2$ quasinormal mode with an exact Chebyshev solve. The mass-normalized spectrum differs from Schwarzschild by about $22\%$, whereas no statistically resolved direct $\alpha$-dependence appears within the conservative spectral envelope over $0\le \alpha/M^2\le 0.3$. We also construct a coupled physics-informed neural network for the unreduced two-field eigenproblem and use it to benchmark the inadmissible comparison branch. A closure-level audit of the anchored family shows positive diagnostic combinations associated with the null, weak, and dominant energy conditions, denominator safety in the modified balance law, and an effective exterior mass fraction of about $20\%$, while indicating that the constant-$(w_r,w_t)$ model should be read as an effective anisotropic stress rather than as a microphysical fluid. Within this closure, the main observable imprint in axial ringdown comes from the existence of the matter-supported branch itself, not from direct variation of the trace coupling.

gr-qc↗

arXiv2026

Cosmological bouncing solutions and their stability in teleparallel gravity

The cosmological dynamics in the early universe are investigated to explore the possibility of the sign reversal of the Hubble parameter as a key feature of non-singular bouncing cosmological solutions in higher-order torsion gravity. The self-consistent multiple cosmological regimes are studied, such as the accelerated expansion, ultra-relativistic, radiation-dominated, sub-relativistic, dust, and stiff matter phases, for three distinct parametrizations of the scale factor: power-law, exponential, and hybrid forms. In particular, five characteristic bouncing scenarios are analyzed: symmetric bounce, super-bounce, oscillatory bounce, matter bounce, and Type IV singularity-free bounce, so that the gravitational Lagrangian can be reconstructed to satisfy bounce conditions at the bounce time. It is found that each scenario requires a violation of the null energy condition, implying the presence of exotic matter with an effective equation of state to drive both the bounce and late-time cosmic acceleration. As a result, it is explicitly demonstrated that higher-order torsion gravity naturally incorporates the bouncing solutions without introducing ad hoc matter fields, providing a possible geometric framework for non-singular early universe evolution. Furthermore, the consistency of the bouncing solutions with the observational constraints of the cosmic microwave background and gravitational wave spectrum is shown, while offering testable predictions for primordial perturbations.

gr-qc↗

arXiv2025

Chemical classification program synthesis using generative artificial intelligence

Accurately classifying chemical structures is essential for cheminformatics and bioinformatics, including tasks such as identifying bioactive compounds of interest, screening molecules for toxicity to humans, finding non-organic compounds with desirable material properties, or organizing large chemical libraries for drug discovery or environmental monitoring. However, manual classification is labor-intensive and difficult to scale to large chemical databases. Existing automated approaches either rely on manually constructed classification rules, or are deep learning methods that lack explainability. This work presents an approach that uses generative artificial intelligence to automatically write chemical classifier programs for classes in the Chemical Entities of Biological Interest (ChEBI) database. These programs can be used for efficient deterministic run-time classification of SMILES structures, with natural language explanations. The programs themselves constitute an explainable computable ontological model of chemical class nomenclature, which we call the ChEBI Chemical Class Program Ontology (C3PO). We validated our approach against the ChEBI database, and compared our results against deep learning models and a naive SMARTS pattern based classifier. C3PO outperforms the naive classifier, but does not reach the performance of state of the art deep learning methods. However, C3PO has a number of strengths that complement deep learning methods, including explainability and reduced data dependence. C3PO can be used alongside deep learning classifiers to provide an explanation of the classification, where both methods agree. The programs can be used as part of the ontology development process, and iteratively refined by expert human curators.

cs.AI↗

arXiv2024

Design, fabrication and testing of Al/p-Si Schottky and pn junctions for radiation studies

Strip and pixels sensors, fabricated on high resistivity silicon substrate, normally of p-type, are used in detectors for High Energy Physics (HEP) typically in a hybrid detector assembly. Furthermore, and owing to their inherent advantages over hybrid sensors, Monolithic Active Pixel Sensors (MAPS) fabricated in CMOS technology have been increasingly implemented in HEP experiments. In all cases, their use in higher radiation areas (HL-LHC and beyond) will require options to improve their radiation hardness and time resolution. These aspects demand a deep understanding of their radiation damage and reliable models to predict their behaviours at high fluences. As a first step, we fabricated several Schottky and n-on-p diodes, to allow a comparison of results and provide a backup solution for test devices, on 6 or 4-inch p-type silicon wafers with 50 μm epitaxial thickness and of doping concentration as they are normally used in HEP detectors and CMOS MAPS devices. In this paper, details of the design and fabrication process, along with test results of the fabricated devices before irradiation, will be provided. Additional test results on irradiated devices will be provided in subsequent publications.

physics.ins-det↗

arXiv2024

Impact of Tolman-Kuchowicz Potentials on Gauss-Bonnet Gravity and Isotropic Stellar Structures

In this manuscript, we study the behavior of charged isotropic compact stellar objects within the framework of the modified Gauss-Bonnety theory of gravity by considering the Tolman Kuchowicz spacetime. We use some matching conditions of spherically symmetric space-time with Bardeen model as an exterior geometry and examine the physical behavior of stellar structures. In the current analysis, we discuss the energy conditions to check the viability of our model. Many physical aspects have been examined, such as energy density, pressure evolution, equation of state parameter, and causality condition. Furthermore, an equilibrium condition can be visualized through the modified Tolman-Oppenheimer-Volkov equation. Further, we study mass-radius function, compactness and redshift function, which are some essential features of the charged compact star model. It is worthwhile to mention here for the current study that our stellar structure in the background of Bardeen's model is more viable and stable.

gr-qc↗

arXiv2024

Anisotropic Quark Stars in Modified $f(R,T)$ Gravity utilizing Tolman V potential

Alternative gravity theory is currently an incredibly significant technique for addressing some enduring experimental difficulties, such as the universe's dark region. They may also be employed in celestial cosmology, producing results that are a stage beyond those found using Einstein's General Relativity. In this study, we examine the characteristics of anisotropic spherically symmetric stellar structures in the context of modified $f(R,T)$ gravity. In order to explain the distinctive characteristics of compact objects, we investigate how the fluid distribution in the star model is affected by the MIT bag model equation of state. By using Tolman V metric potentials, we establish the field equations, and by employing the experimental data of the three observed stars, we identify the values of unknown parameters. By using a realistic $f(R,T)$ model, we investigate the effect of the energy density, anisotropic factor, transversal and radial pressure within the cores of the aforementioned stars for a particular amount of the Bag constant. Further, we examine the stability of the cosmic structure and the physical validity of our suggested model via equilibrium conditions, energy, and causality parameters. To conclude, the physical conditions are fulfilled by our model, and the magnitude of the Bag constant agrees with the experimental data, demonstrating the model's feasibility.

gr-qc↗

arXiv2024

Impact of Ricci Inverse Gravity on Hybrid Star Model

The objective of our current study is to explore novel aspects of a stationary anisotropic relativistic hybrid compact star that consists of quark matter (QM) in its core and ordinary baryonic matter (OBM) in its crust. This study has been done by adopting separate equations of states (EoSs) for quark matter and baryonic matter. The MIT bag model equation of state $p_{q}=\frac{1}{3}(ρ_{q}-4B)$ has been used to demonstrate a correlation between the density and pressure of weird quark matter in the interior of the star. In addition, we present a simple linear equation of state $p_{r}=β_{1}ρ-β$ that links radial pressure and matter density for OBM. The stellar model was formulated within the context of $f(\mathcal{R},\mathcal{A})$ gravity, utilizing a linear correlation between Ricci tensor $\mathcal{R}$ and anticurvature scaler $\mathcal{A}$.To solve the field equations of this novel alternative gravity, we employ the Krori and Barua approach to the metric potentials. The validity of our suggested model is assessed using the graphical approach, while ensuring that the conditions are physically feasible. Our focus is specifically on the tiny celestial object known as LMC X-4 [$\text{M} = (1.04^{+0.09}_{-0.09})M_{\odot};\text{R}=8.301^{+0.2}_{-0.2}\text{km}$], which we consider a viable candidate for a strange quark star. We want to clarify the model's physical validity by examining a variety of physical assessments, including dynamical equilibrium, energy conditions, compactness factor, mass function, and surface redshift. The resulting outcome confirms the authenticity of the hybrid star model under analysis.

gr-qc↗

arXiv2024

A Study of Levia-Civita and Cosmic String Solutions in Modified $f(R)$ Gravity

In this research manuscript, we explore cylindrically symmetric solutions within the framework of modified $f(R)$ theories of gravity, where $R$ representing the Ricci scalar. The study focuses on analyzing the cylindrical solutions within realistic space-time regions and investigates three distinct cases of exact solutions derived from the field equations of $f(R)$ theory of gravity. Moreover, we examine well-known Levi-Civita and cosmic string solutions for the said modify gravity. Furthermore, the manuscript delves into the implications of the obtained results by exploring energy conditions for each case. Notably, a violation of null energy conditions is observed, suggesting the potential existence of cylindrical wormholes. The findings contribute to the understanding of modified $f(R)$ theories of gravity, providing valuable insights into the nature of cylindrically symmetric solutions and their implications in theoretical physics.

gr-qc↗

arXiv2024

Investigation of Traversable Wormhole Solutions in Modified $f(R)$ Gravity with Scalar Potential

The objective of this manuscript is to investigate the traversable wormhole solutions in the background of the $f(R, ϕ)$ theory of gravity, where $R$ is the Ricci scalar and $ϕ$ is the scalar potential respectively. For this reason, we use the Karmarkar criterion for traversable static wormhole geometry to create a wormhole shape function. The suggested shape function creates wormhole geometry that links two asymptotically flat spacetime regions and meets the necessary requirements. The embedding diagram in three-dimensional Euclidean space is also discussed in order to demonstrate the wormhole configurations. For our current analysis, we choose the suitable values of free parameters for $f(R, ϕ)$ gravity models to discuss the wormhole geometry. It can be observed that our proposed shape function provides the wormhole solutions with less amount of exotic matter. It can be noticed that energy conditions especially null energy conditions are violated for all considered models. The violation of energy conditions indicates the existence of exotic matter and wormhole geometry. It is concluded that the shape function acquired through the Karmarkar technique yields validated wormhole configurations with even less exotic matter correlating to the chosen $f(R, ϕ)$ gravity models.

gr-qc↗

arXiv2024

Anisotropic Spheres Via Embedding Approach in $f(R,ϕ, X)$ Gravity

In this manuscript, we investigate the behavior of stellar structure through embedding approach in $f(R, ϕ, X)$ modified theory of gravity, where $R$ denotes the Ricci scalar, $ϕ$ represents the scalar potential and $X$ indicates the kinetic potential. For this purpose, we consider the spherically symmetric space-time with anisotropic fluid. We further choose three different stars i.e. LMC X-4, Cen X-3, and EXO 1785-248 to demonstrate the behavior of stellar structures. We further compare the Schwarzschild space-time as exterior geometry with spherically symmetric space-time to calculate the values of unknown parameters. In this regard, we investigate the graphical features of stellar spheres such es energy density, pressure components, anisotropic component, equation of state parameters, stability analysis and energy conditions. Furthermore, we investigate some extra conditions such as mass function, compactness factor and surface redshift respectively. Conclusively, all the compact stars under observations are realistic, stable, and are free from any physical or geometrical singularities. We find that the embedding class one solution for anisotropic compact stars is viable and stable.

gr-qc↗

arXiv2024

$f(R, T)$ Gravity Bouncing Universe with Cosmological Parameters

The basic aim of this manuscript is to investigate the cosmological solutions in the context of the modified $f(R, T)$ theory of gravity, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. For our current work, we consider the Friedmann-Robertson-Walker space-time for finding the solutions of field equations. We investigate the nature of universe by considering acceleration expansion of universe, ultra relativistic universe, sub-relativistic universe, dust universe, radiation universe, stiff universe. Moreover, we apply the power law technique by taking two different $f(R, T)$ gravity models to observe the expanding nature of the universe. The bouncing scenario is also discussed by choosing some particular values of the model parameters and observed the energy conditions, which are satisfied for a successful bouncing model. It is also concluded that some solutions in $f(R, T)$ theory of gravity supports the concept of exotic matter and accelerated expansion of the universe due to a large amount of negative pressure.

gr-qc↗

arXiv2023

Observational constraints on a logarithmic scalar field dark energy model and black hole mass evolution in the Universe

We propose a logarithmic parametrization form of energy density for the scalar field dark energy in the framework of the standard theory of gravity, which supports the necessary transition from the decelerated to the accelerated behavior of the Universe. The model under consideration is constrained by available observational data, including cosmic chronometers data-sets (CC), Baryonic Acoustic Oscillation (BAO) data-sets, and Supernovae (SN) data-sets, consisting of only two parameters $α$ and $β$. The combined $CC$+$BAO$+$SN$ data-sets yields a transition redshift of $z_{tr}=0.79^{+0.02}_{-0.02}$, where the model exhibits signature-flipping and is consistent with recent observations. For the combined data-sets, the present value of the deceleration parameter is calculated to be $q_{0}=-0.43^{+0.06}_{-0.06}$. Furthermore, the analysis yields constraints on both the parameter density value for matter and the present value of the Hubble parameter, with values of $Ω_{m0}=0.25849^{+0.00026}_{-0.00025}$ and $H_{0}=67.79_{-0.59}^{+0.59}$ $km/s/Mpc$, respectively, consistent with the results obtained from Planck 2018. Finally, the study investigates how the mass of a black hole evolves over time in a Universe with both matter and dark energy. It reveals that the black hole mass increases initially but stops increasing as dark energy dominates.

gr-qc↗

arXiv2023

Physical Characteristics and Maximum Allowable Mass of Hybrid Star in the Context of $f(Q)$ Gravity

In this study, we explore several new characteristics of a static anisotropic hybrid star with strange quark matter (SQM) and ordinary baryonic matter (OBM) distribution. Here, we use the MIT bag model equation of state to connect the density and pressure of SQM inside stars, whereas the linear equation of state $p_r =αρ-β$ connects the radial pressure and matter density caused by baryonic matter. The stellar model was developed under a background of $f(Q)$ gravity using the quadratic form of $f(Q)$. We utilized the Tolman-Kuchowicz ansatz to find the solutions to the field equations under modified gravity. We have matched the interior solution to the external Schwarzschild spacetime in order to acquire the numerical values of the model parameters. We have selected the star Her X-1 to develop various profiles of the model parameters. Several significant physical characteristics have been examined analytically and graphically, including matter densities, tangential and radial pressures, energy conditions, anisotropy factor, redshirt, compactness, etc. The main finding is that there is no core singularity present in the formations of the star under investigation. The nature of mass and the bag constant $B_g$ have been studied in details through equi-mass and equi-$B_g$ contour. The maximum allowable mass and the corresponding radius have been obtained via $M-R$ plots.

gr-qc↗

arXiv2023

Study of Embedded Class-I Fluid Spheres in $f(R,T)$ Gravity with Karmarkar Condition

In this article, we explore some emerging properties of the stellar objects in the frame of the $f(R,T)$ gravity by employing the well-known Karmarkar condition, where $R$ and $T$ represent Ricci scalar and trace of energy momentum tensor respectively. It is worthy to highlight here that we assume the exponential type model of $f(R,T)$ theory of gravity $f(R,T)=R+α(e^{-βR}-1)+γT$ along with the matter Lagrangian $\mathcal{L}_{m}=-\frac{1}{3}(p_{r}+2 p_{t})$ to classify the complete set of modified field equations. We demonstrate the embedded class-I technique by using the static spherically symmetric line element along with anisotropic fluid matter distribution. Further, to achieve our goal, we consider a specific expression of metric potential $g_{rr}$, already presented in literature, and proceed by using the Karmarkar condition to obtain the second metric potential. In particular, we use four different compact stars, namely $LMC~X-4,$ $EXO~1785-248,$ $Cen~X-3$ and $4U~1820-30$ and compute the corresponding values of the unknown parameters appearing in metric potentials. Moreover, we conduct various physical evolutions such as graphical nature of energy density and pressure progression, energy constraints, mass function, adiabatic index, stability and equilibrium conditions to ensure the viability and consistency of our proposed model. Our analysis indicates that the obtained anisotropic outcomes are physically acceptable with the finest degree of accuracy.

gr-qc↗

arXiv2023

Relativistic Krori-Barua Compact Stars in $f(R,T)$ Gravity

This work aims to investigate the behaviour of compact stars in the background of $f(R, T)$ theory of gravity. For current work, we consider the Krori-Barua metric potential i.e., $ν(r)= Br^2+C$ and $λ(r)= Ar^2,$ where, $A, B$ and $C$ are constants. We use matching conditions of spherically symmetric space-time with Schwarzschild solution as an exterior geometry and examine the physical behaviour of stellar structure by assuming the exponential type $f(R, T)$ gravity model. In the present analysis, we discuss the graphical behaviour of energy density, radial pressure, tangential pressure, equation of state parameters, anisotropy and stability analysis respectively. Furthermore, an equilibrium condition can be visualized through the modified Tolman-Oppenheimer-Volkov equation. Some extra features of compact stars i.e. mass-radius function, compactness factor and surface redshift have also been investigated. Conclusively, all the results in current study validate the existence of compact stars under exponential $f(R, T)$ gravity model.

gr-qc↗

arXiv2020

Knowledge Diffusion Process & Common Islamic Banking Governance Principles: Integrative Perspective (s) of Managers and Shariah Scholars

Islamic banks being commercial entities strive to earn profit within shariah ambit. Therefore, they seem to be basing themselves upon two knowledge streams namely i) Islamic jurisprudence principles, and ii) banking principles. Islamic jurisprudence principles primarily aim at bringing shariah compliance while banking principles focus profitability. These principles, making two schools of thought in the discipline, however, have their unique philosophies, principles, and practices, which are now gradually diffusing into an emergent set of governance principles basing the contemporary Islamic banking theory and practice. Governance systems of Islamic banks have elements of both conventional as well as Shariah, and need to have principles having components of banking and shariah sufficiently diffused for their successful operations in a longer term. Aim of this research is to review the literature about the knowledge diffusion process of islamic banking principles which guides the governance of Islamic banks. This study review the literature using a method in which focus remain on bridging different areas which in this case are knowledge diffusion and islamic banking governance principles.

q-fin.GN↗