arXiv subjects

Madiha Ajmal

Publications and source records attributed to Madiha Ajmal.

8 recordsLinked to original sources

arXiv2026

Exploring Hybrid Star Models with Quark and Hadronic Matter in $f(Q)$ Gravity

In this paper, we develop a model for a static anisotropic hybrid star that includes strange quark matter and hadronic matter. We solve the field equations in the $f(Q)$ gravity framework (where $Q$ is the non-metricity) using the Finch-Skea metric. The relationship between density and pressure for strange quark matter is described using the MIT bag model equation, while for hadronic matter, the radial pressure and density are related by a linear equation of state. We select the compact star EXO 1785-248 and analyze five different values of the coupling constant. To evaluate the physical feasibility of the model, we perform a graphical analysis of key properties, including the metric components, energy density, radial and tangential pressures, anisotropy, gradients, quark matter density and pressure, the equation of state parameter, energy conditions and the mass function. We further examine the stability and equilibrium of the star through parameters such as compactness, redshift, causality conditions, Herrera cracking, the adiabatic index and the Tolman-Oppenheimer-Volkoff equation. We observe that $f(Q)$ gravity effectively describes the macroscopic properties of hybrid stars.

gr-qc↗

arXiv2025

Non-Interacting New Agegraphic Dark Energy Model in $f(Q)$ Gravity

In this study, we explore the reconstruction of a new agegraphic dark energy model in a flat Friedmann-Robertson-Walker spacetime by $f(Q)$ gravity framework, where $Q$ represents non-metricity. We assume that the scale factor follows a power-law and explore how this model aligns with the expanding universe. In this perspective, we develop a new agegraphic $f(Q)$ model and analyze the graphical behavior for cosmic evolution. We analyze physical characteristics of the model using the equation of state parameter, $(ω_{D}-ω^{\prime}_{D})$ and the $(r-s)$ planes. The equation of state parameter indicates a quintessence era characterized by accelerated expansion. The $(ω_{D}-ω^{\prime}_{D})$-plane identifies the freezing region and the Chaplygin gas model is represented in the $(r-s)$-plane. Finally, we examine the stability of the non-interacting model by evaluating the squared speed of sound. Our findings show that the non-interacting new agegraphic dark energy model effectively resolves the cosmic coincidence problem.

gr-qc↗

arXiv2025

Cosmography of Non-Interacting Ghost and Generalized Ghost Dark Energy Models in f(Q) Gravity

This paper aims to develop non-interacting ghost dark energy and generalized ghost dark energy models within the framework of $f(Q)$ theory using the correspondence scheme. We use pressureless matter and a power-law scale factor. The cosmic implications of the resulting models are studied through the equation of state parameter and the phase planes. We also check the stability of the reconstructed models through the squared speed of sound parameter. The equation of state parameter exhibits a phantom era, the $(ω_{D}-ω^{\prime}_{D})$-plane indicates a freezing region, while the $(r-s)$-plane corresponds to the Chaplygin gas model for both models. It is also found that only the generalized ghost dark energy model remains stable throughout cosmic evolution. We conclude that our findings align well with current observational data.

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arXiv2025

Charged Gravastar Solutions in the Finch-Skea Framework with f(\mathbb{Q}) Gravity

In this study, we investigate the features of a charged gravastar within the framework of $f(\mathbb{Q})$ gravity ($\mathbb{Q}$ represents non-metricity) using the Finch-Skea metric. This metric is applied to both the interior and shell regions of the charged gravastar and the field equations are derived accordingly. For the exterior regions, we consider various black holes, i.e., Reissner-Nordstr$\ddot{o}$m, Bardeen and Hayward regular black holes. The interior and exterior layers are matched using the Israel junction conditions, which help to determine the surface energy density and surface pressure for these black holes. We examine some physical properties such as proper length, entropy, energy and the equation of state parameter. The stability of the developed gravastar model is discussed through the effective potential, the causality condition and adiabatic index. We conclude that the compact gravastar structure could be a viable alternative to black holes within this framework.

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arXiv2025

New Agegraphic Dark Energy Model in Modified Symmetric Teleparallel Theory

In this manuscript, we examine the cosmological significance of the new agegraphic dark energy model by investigating different cosmological parameters such as the equation of state parameter, $ω_{D}-ω^{\prime}_{D}$ and the $r-s$ planes in the framework of $f(\mathcal{Q})$ theory. We consider flat Friedmann-Robertson-Walker universe model under interacting conditions between dark energy and dark matter. The equation of state parameter indicates a quintessence-like characteristic of the universe. The stability of the model is analyzed using the squared speed of sound parameter which demonstrates the unstable behavior of the new agegraphic dark energy model throughout the cosmic evolution. The freezing region is represented by the $ω_{D}-ω^{\prime}_{D}$ plane, while the Chaplygin gas model corresponds to the $r-s$ plane. It is worthwhile to mention here that the interacting new agegraphic dark energy model addresses the cosmic coincidence problem by allowing the energy density ratio between dark energy and dark matter to evolve slowly over cosmic time.

gr-qc↗

arXiv2024

Impact of Charge on the Stability of Pulsar SAX J1748.9-2021 in Modified Symmetric Teleparallel Gravity

In this paper, we explore the effect of charge on the stability of pulsar star SAX J1748.9-2021 in $f(Q)$ gravity, where $Q$ represents non-metricity. For this purpose, we apply the Krori-Barua metric ansatz with anisotropic fluid and use a linear $f(Q)$ model $f(Q)=ζQ$, where $ζ$ is a non-zero constant. We derive exact relativistic solutions of the corresponding field equations. Furthermore, we study its geometric and physical properties through astrophysical observations from the pulsar SAX J1748.9-2021, which is found in X-ray binary systems within globular clusters. We examine features like anisotropic pressure, the mass-radius relationship, redshift, the Zeldovich condition, energy and causality conditions, the adiabatic index, the Tolman-Oppenheimer-Volkoff equation, the equation of state parameter and compactness. Our findings align with the observational data which indicate that the pulsar SAX J1748.9-2021 is viable and stable under this modified theory of gravity.

gr-qc↗

arXiv2024

Pilgrim and Generalized Ghost Pilgrim Dark Energy Models in Modified Symmetric Teleparallel Gravity

In this paper, we investigate $f(Q)$ gravity ($Q$ represents the non-metricity) to explore its cosmological implications of the two non-interacting dark energy models. We use the correspondence scenario to find the pilgrim and generalized ghost pilgrim dark energy $f(Q)$ gravity models for a Friedmann-Robertson-Walker universe with pressureless matter and a power-law scale factor. The reconstructed models explain the observed rapid expansion of the universe using astronomical observations. We also examine the physical properties of the model, including its equation of state parameter, $(ω_{D}-ω^{\prime}_{D})$ and $(r-s)$-planes and the squared speed of sound. It is found that our results are consistent with the interacting pilgrim dark energy model in the same gravity.

gr-qc↗

arXiv2024

Generalized Ghost Dark Energy in f(Q) Gravity

In this manuscript, we use the correspondence principle to construct the generalized ghost dark energy $f(Q)$ model, where $Q$ is the non-metricity. For this purpose, we use the Friedman-Robertson-Walker universe model with power-law scale factor. The energy density in this model linearly depends on the Hubble parameter, with a sub-leading term of $H^{2}$, resulting in an energy density $ρ_D=ξH+ζH^{2}$, where $ξ$ and $ζ$ are arbitrary constants. We reconstruct interacting fluid scenario of this dark energy with dark matter. The reformulated $f(Q)$ gravity model shows how different epochs of the cosmic history can be reproduced by this modified gravity model. The physical characteristics of the model are discussed through the equation of state parameter with the planes of $ω_{D}-ω'_{D}$ and $r-s$. We also explore the stability criteria for the interacting model using the squared speed of sound. The equation of state parameter indicates phantom phase of the universe and the squared speed of sound represents stability of the interacting model. The $(ω_{D}-ω^{\prime}_{D})$-plane indicates freezing region, while the $(r-s)$-plane corresponds to the Chaplygin gas. We conclude that our findings coincide with the latest observational data.

gr-qc↗