arXiv subjects

M. Ilyas

Publications and source records attributed to M. Ilyas.

At least 19 recordsLinked to original sources

arXiv2026

Parameter Space, Realistic Matter, and Universal Relations in Bose--Einstein Condensate Dark Stars

We study slowly rotating Bose--Einstein condensate (BEC) dark stars by solving the Tolman--Oppenheimer--Volkoff, Hartle dipole, and Postnikov--Hinderer equations together for a polytropic equation of state with a Lee--Huang--Yang correction of strength $\zeta$~\citep{Panotopoulos2026}. A continuous scan of $\zeta$ from 0 to 1.5 shows the mean-field-to-corrected transition is smooth, with no hidden structure at intermediate values. Scanning the underlying boson parameters $(m,a_s)$ more broadly, we find that a $2\,M_\odot$ maximum-mass bound and a GW170817-like tidal bound $\Lambda_{1.4}\lesssim800$ cannot be satisfied simultaneously anywhere in this equation-of-state class. The $I$-Love universal relation holds to $0.13\%$ across twelve $(m,a_s,\zeta)$ models, and the $\zeta=0$ and $\zeta=1$ sequences sit on opposite sides of the master curve by a consistent, non-random offset. Applied without modification to realistic nuclear matter (SLy, APR4), the same solver reproduces published maximum masses to within $1\%$; applied to self-bound MIT-bag quark matter it gives the expected mass--radius shape; and once extended to a two-fluid baryon-plus-dark-matter formalism, it shows that the maximum mass of a hybrid star is not a monotonic function of the central dark-matter fraction. Pooling $I$-Love sequences across nuclear, hybrid, and BEC dark-star models, we find they collapse onto a single curve to within about $5\%$, while self-bound quark stars sit far off it, departing by up to $90\%$.

gr-qc↗

arXiv2026

Regular Fuzzy Dark Matter Black Holes and Their Horizon Structure

We construct regular, horizon-admitting compact objects supported entirely by a self-gravitating dark-matter fluid, in the one-parameter curvature-gravity family $f(R)=R+\beta R^n$. Working with the Einasto density profile, we derive the anisotropic fluid field equations for a static, spherically symmetric metric and obtain the exact General Relativity limit under a de~Sitter-type equation of state, in which the central singularity is replaced by a regular de~Sitter core and the solution is either a horizonless droplet or a black hole with one or two Killing horizons, depending on a single rescaled-mass parameter. We compute the resulting Hawking temperature and geodesic effective potential, and -- exploiting the linearity of the $\beta=0$ field equation -- solve the curvature correction perturbatively in closed form for general $n$, showing that its sign and radial shape are genuinely model-dependent by direct comparison at fixed $\beta$ between $n=2$ (Starobinsky) and $n=3$ (cubic) gravity. We repeat the construction for a non-local equation of state and confirm the resulting droplets are curvature-regular via the Kretschmann scalar. Finally, replacing the Einasto profile with the cored Burkert profile preserves the qualitative regularity mechanism but, because the Burkert halo lacks a finite total mass, produces a horizon structure with inner and outer radii separated by nearly three orders of magnitude -- a genuine physical distinction between two comparably realistic dark-matter models.

physics.gen-ph↗

arXiv2025

Karmarkar-Tolman Embedded Charged Anisotropic Stars in f(R) Gravity

We investigate various anisotropic spherical distributions of charged celestial bodies within the context of f(R) gravity, where R represents the Ricci scalar. The properties of specific charged compact objects are analyzed by using the Karmarkar-Tolman spacetime and three distinct gravitational models. The behavior of the structural parameters is examined via graphical methods. Energy constraints are applied to assess how well the results align with the Karmarkar-Tolman spacetime model. The physical acceptability of the stellar models is evaluated by checking the energy conditions and the equation of state parameter. Additionally, we explore the influence of anisotropy on the stability and internal structure of the models. Our findings are compared with predictions from general relativity to highlight the effects of f(R) gravity on charged compact stars. The obtained results are useful to enhance our understanding of how modified gravity theories affect the properties of compact astrophysical objects.

gr-qc↗

arXiv2023

Traversable wormholes with static spherical symmetry and their stability in higher-curvature gravity

The solutions of traversable wormholes and their geometries are investigated in higher-curvature gravity with boundary terms for each case under the presence of anisotropic, isotropic and barotropic fluids in detail. For each case, the effective energy-momentum tensor violates the null energy condition throughout the wormhole throat. The null and weak energy conditions are also analyzed for ordinary matters. The regions that physically viable wormhole solutions can exist are explicitly shown. Furthermore, it is found that the range of the viable regions exhibits an alternating pattern of expansion and contraction. The present analyses can reveal the regions in which traversable wormholes can be constructed for anisotropic, isotropic and barotropic fluids cases with incorporating realistic matter contents, leading to fundamental physics insights into the feasible construction of wormholes in higher-curvature gravity with boundary term. The main achievements of this work, in contrast to previous studies, are its thorough investigation of traversable wormholes within the framework of higher-curvature gravity with boundary terms, its extensive consideration of various fluid types, and the explicit identification of regions where stable wormhole solutions can exist.

gr-qc↗

arXiv2023

Effects of $f (R, G)$ gravity on anisotropic charged compact objects

The present study provides an in-depth analysis of the anisotropic matter distribution and various physical aspects of compact stars in the context of a $f(R,G)$-gravity framework. In order to gain an exhaustive understanding of these aspects, our study focuses on three particular compact stars: VELA X-1 (CS1), SAXJ1808.4-3658 (CS2), and 4U1820-30 (CS3). We conducted calculations on the relevant characteristics of these compact stars by employing three different models of $f(R,G)$-gravity. As a convenient approach, the $f(R,G)$-gravity is organized into two distinct components, which include $f_1(R)$ and $f_2(G)$. The $R$ dependent component is modeled similarly to the Hu-Sawicki approach, while for modeling the $G$ dependent component, we chose logarithmic and power law-like approaches and suggested three viable gravity models. Graphical methods are used to analyze the physical properties of the compact stars in the domain of suggested models of gravity.

gr-qc↗

arXiv2023

Holographic Schwinger effect with a rotating probe D3-brane

This paper, among other things, talks about possible research on the holographic Schwinger effect with a rotating probe D3-brane. We discover that for the zero temperature case in the Schwinger effect, the faster the angular velocity and the farther the distance of the test particle pair at D3-brane, the potential barrier of total potential energy also grows higher and wider. This paper shows that at a finite temperature, when $S^5$ without rotation is close to the horizon, the Schwinger effect fails because the particles remain in an annihilate state, which is an absolute vacuum state. However, the angular velocity in $S^5$ will avoid the existence of an absolute vacuum near the horizon. For both zero and finite temperature states, the achieved results completely agree with the results of the Dirac-Born-Infeld (DBI) action. So the theories in this paper are consistent. All of these show that these theories will play important roles in future pair production research.

hep-th↗

arXiv2023

Charged Compact Stars in Extended $f(\mathcal{R},\mathcal{G},\mathcal{T})$ Gravity

The purpose of this paper is to study charged compact stars using extended gravitational theory, also known as $f(\mathcal{R}, \mathcal{G}, \mathcal{T})$ gravity. Alternatively, this theory is also called $f(\mathcal{R}, \mathcal{T}, \mathcal{G})$ gravity. The symbols $\mathcal{R}, \mathcal{G}$, and $\mathcal{T}$ denote the Ricci Scalar, the Gauss-Bonnet invariant, and the trace of the energy-momentum tensor, respectively. We suggested several plausible models in the framework of this new gravity theory, and then used these models to explore several physical properties of compact objects of relativistic nature. This research also takes into account three famous compact stars: Vela X-1 (CS1); SAXJ1808.4-3658 (CS2); and 4U1820-30 (CS3). Moreover, using the suggested models, the physical nature of anisotropic stress, energy density, various energy conditions (ECs), the state of equilibrium, interior stability, mass variations, compactness, anisotropy, electric charge, and electric field intensity are analysed for considered compact stars. Different plots of the above-mentioned quantities are presented for this analysis. Conclusively, the ECs are satisfied, and the compact stars have a significant dense core.

gr-qc↗

arXiv2022

Energy Conditions in Extended $f(R,G,T)$ Gravity

In this paper, we consider the flat Friedmann Lematre Robertson-Walke metric in the presence of perfect fluid models and extended $f(R,G,T)$ gravity (where $R$ is the Ricci scalar, $G$ is the Gauss Bonnet invariant and $T$ stands for trace of energy momentum tensor). In this context, we assume some specific realistic $f(R,G,T)$ models configuration that could be used to explore the finite-time future singularities that arise in late-time cosmic accelerating phases. In this scenario, we choose the most recent estimated values for the Hubble, deceleration, snap and jerk parameters to develop the viability and bounds on the models parameters induced by different energy conditions.

gr-qc↗

arXiv2022

Some Specific Wormhole Solutions in Extended $f(R,G,T)$ Gravity

This research work provides an exhaustive investigation of the viability of different coupled wormhole (WH) geometries with the relativistic matter configurations in the $f(R,G,T)$ extended gravity framework. We consider a specific model in the context of $f(R,G,T)$-gravity for this purpose. Also, we assume a static spherically symmetric space-time geometry and a unique distribution of matter with a set of shape functions ($\beta(r)$) for analyzing different energy conditions (ECs). In addition to this, we examined WH-models in the equilibrium scenario by employing anisotropic fluid. The corresponding results are obtained using numerical methods and then presented using different plots. In this case, $f(R,G,T)$ gravity generates additional curvature quantities, which can be thought of as gravitational objects that maintain irregular WH-situations. Based on our findings, we conclude that in the absence of exotic matter, WH can exist in some specific regions of the parametric space using modified gravity model as, $f(R,G,T) = R +\alpha R^2+\beta G^n+\gamma G\ln(G)+\lambda T$.

gr-qc↗

arXiv2022

Compact relativistic geometries in $f(R,G)$ gravity

One of the possible potential candidates for describing the universe's rapid expansion is modified gravity. In the framework of the modified theory of gravity $f(R,G)$, the present work features the materialization of anisotropic matter, such as compact stars. Specifically, to learn more about the physical behavior of compact stars, the radial, and tangential pressures as well as the energy density of six stars namely $Her X-1$, $SAXJ1808.4-3658$, $4U1820-30$, $PSR J 1614 2230$, $VELA X-1$, and $Cen X-3$ are calculated. Herein, the modified theory of gravity $f(R,G)$ is disintegrated into two parts i.e. the $\tanh$ hyperbolic $f(R)$ model and the three different $f(G)$ model. The study focuses on graphical analysis of compact stars wherein the stability aspects, energy conditions, and anisotropic measurements are mainly addressed. Our calculation revealed that, for the positive value of parameter n of the model $f(G)$, all the six stars behave normally.

gr-qc↗

arXiv2021

Compact Stars in $f(\mathcal{R,G,T})$ Gravity

The present work is to introduce a new kind of modified gravitational theory, named as $f(\mathcal{R,G,T})$ (also $f(\mathcal{R,T,G})$) gravity, where $\mathcal{R}$ is the Ricci scalar, $\mathcal{G}$ is Gauss-Bonnet invariant and $\mathcal{T}$ is the trace of the energy-momentum tensor. With the help of different models in this gravity, we investigate some physical features of different relativistic compact stars. For this purpose, we develop the effectively modified field equations, conservation equation, and the equation of motion for test particle. Then, we check the impact of additional force (massive test particle followed by a non-geodesic line of geometry) on compact objects. Furthermore, we took three notable stars named as $Her X-1$, $SAXJ1808.4-3658$ and $4U1820-30$. The physical behavior of the energy density, anisotropic pressures, different energy conditions, stability, anisotropy, and the equilibrium scenario of these strange compact stars are analyzed through various plots. Finally, we conclude that the energy conditions hold, and the core of these stars is so dense.

gr-qc↗

arXiv2021

Bounce cosmology in $f(\mathcal{R})$ gravity

In this paper, we analyze the modified $f(\mathcal{R})$ gravity models in Friedmann--Lema\^ıtre--Robertson--Walker (FLRW) background. The actions of bouncing cosmology are studied under consideration of different viable models in $f(\mathcal{R})$ gravity theory that can resolve the difficulty of singularity in standard Big-Bang cosmology. Under different viable models in $f(\mathcal{R})$ gravity theory, the cosmological constraints are plotted in provisions of cosmic-time, then investigated the bounce circumstance. In addition, the red-shift parameter is used to reconstruct the modified gravity, and compile the cosmological parameters that infer accelerated universe expansion. Finally, the situation stability is evaluated with a sound speed feature, which illustrates late-time stability.

gr-qc↗

arXiv2019

Energy Conditions in Non-local Gravity

We investigate the different energy conditions in nonlocal gravity, which is obtained by adding an arbitrary function of d'Alembertian operator, $f(\Box^{-1})$, to the Hilbert- Einstein action. We analyze the validity of four different energy conditions and illustrate the different constraints over parameters of the power law solution as well as de Sitter solution.

gr-qc↗

arXiv2019

Bounds on Higher Derivative $f(R,\square R,T)$ Models from Energy Conditions

This paper studies the viable regions of some cosmic models in a higher derivative $f(R,\square R, T)$ theory with the help of energy conditions (where $R$ and $T$ are the Ricci scalar, and trace of energy momentum tensor, respectively). For this purpose, we assume a flat Friedmann-Lemaître-Robertson-Walker metric which is assumed to be filled with perfect fluid configurations. We take two distinct realistic models, that might be helpful to explore stable regimes of cosmological solutions. After taking some numerical values of cosmic parameters, like crackle, snap, jerk (etc) as well as viable constraints from energy conditions, the viable zones for the under observed $f(R,\square R, T)$ models are examined.

gr-qc↗

arXiv2018

Energy Conditions in Higher Derivative $f(R,\Box R,T)$ Gravity

In this paper, we examined the viability bounds of a higher derivative $f(R,\Box R, T)$ theory through analyzing energy conditions (where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor, respectively). We take flat Friedmann-Lemaître-Robertson-Walker spacetime coupled with ideal configurations of matter content. We consider three different realistic models of this gravity, that could be utilized to understand the stability of cosmological solutions. After constructing certain bounds mediated by energy conditions, more specifically weak energy condition, we discuss viable zones of the under considered modified models in an environment of recent estimated numerical choices of the cosmic parameters.

gr-qc↗

arXiv2018

Existence of Compact Structures in $f(R,T)$ Gravity

The present paper is devoted to investigate the possible emergence of relativistic compact stellar objects through modified $f(R,T)$ gravity. For anisotropic matter distribution, we used Krori and Barura solutions and two notable and viable $f(R,T)$ gravity formulations. By choosing particular observational data, we determine the values of constant in solutions for three relativistic compact star candidates. We have presented some physical behavior of these relativistic compact stellar objects and some aspects like energy density, radial as well as transverse pressure, their evolution, stability, measure of anisotropy and energy conditions.

physics.gen-ph↗

arXiv2017

Influence of $f(R)$ Models on the Existence of Anisotropic Self-Gravitating Systems

This paper aims to explore some realistic configurations of anisotropic spherical structures in the background of metric $f(R)$ gravity, where $R$ is the Ricci scalar. The solutions obtained by Krori and Barua are used to examine the nature of particular compact stars with three different modified gravity models. The behavior of material variables is analyzed through plots and the physical viability of compact stars is investigated through energy conditions. We also discuss the behavior of different forces, equation of state parameter, measure of anisotropy and Tolman-Oppenheimer-Volkoff equation in the modeling of stellar structures. The comparison from our graphical representations may provide evidences for the realistic and viable $f(R)$ gravity models at both theoretical and astrophysical scale.

gr-qc↗

arXiv2017

Evolution of Compact Stars and Dark Dynamical Variables

This work is aimed to explore the dark dynamical effects of $f(R,T)$ modified gravity theory on the dynamics of compact celestial star. We have taken the interior geometry as spherical star which is filled with imperfect fluid distribution. The modified field equations are explored by taking a particular form of $f(R,T)$ model, i.e., $f(R,T)=f_1(R)+f_2(R)f_3(T)$. These equations are then utilized to formulate the well-known structure scalars under the dark dynamical effects of this higher order gravity theory. Also, the evolution equations for expansion and shear are formulated with the help of these scalar variables. Further, all this analysis have been made under the condition of constant $R$ and $T$. We found a crucial significance of dark source terms and dynamical variables on the evolution and density inhomogeneity of compact objects.

gr-qc↗