arXiv subjects

Nusrat Fatima

Publications and source records attributed to Nusrat Fatima.

4 recordsLinked to original sources

arXiv2026

A Non-Singular Cosmic Bounce in $\mathcal{F}(Q)$ Gravity: A Reconstruction and Phase Space Analysis

The key focus of this research work is the analysis of a non-singular cosmic bounce in the context of $\mathcal{F}(Q)$ gravity, with $Q$ representing the non-metricity scalar. We consider the gravitational Lagrangian $\mathcal{F}(Q)=Q+\psi Q^n$ in the presence of a modified Chaplygin-type matter source with a flat Friedmann-Robertson-Walker spacetime and a perfect matter distribution. In order to proceed, we adopt two approaches: a reconstruction approach using scale-factor ansatz and analysis of a two-dimensional autonomous dynamical system. Our results imply that the geometry coupling parameter $\psi$ plays an important role and causes geometrical repulsion for violating the null energy condition. A numerical scan of the $(\rho_0,\psi)$ parameter space suggests that there is a critical energy density for the bounce to take place, below which the universe evolves towards the standard singular cosmological solution. Moreover, the effective equation of state slowly evolves towards the de Sitter value ($\omega_{eff}\rightarrow -1$) and the squared sound speed is bounded by the stability and causality condition ($0\leq C_s^2\leq1$). It is found that $\mathcal{F}(Q)$ gravity provides a coherent geometric picture of the non-singular bouncing universe in accordance with the cosmic accelerated expansion.

gr-qc↗

arXiv2026

Bulk Viscosity and Thermodynamic Approaches to Singularity Resolution in Non-Metric Gravity

This manuscript investigates the impact of bulk viscosity on the viability of cosmic bounce solutions in the context of $f(\mathcal{Q})$ theory, where $\mathcal{Q}$ is a non-metricity scalar. To complete this objective, we study the behavior of an isotropic homogeneous universe filled with a perfect fluid and consider a innovative parametrization of bulk viscosity coefficient with an arbitrary constant $\zeta_0$ as $\zeta=\zeta_{0}H$. We consider the particular functional form of this modified theory to explore how this gravitational framework influences the cosmic evolution and explore a range of cosmological parameters to assess the existence and physical viability of bounce solutions. We also investigate the evolution of entropy through the second law of thermodynamics. The positive trend of energy density, negative pressure profile and violation of energy conditions support the existence of viable cosmological bounce scenario and highlights the significance of bulk viscosity in this framework. These results demonstrate that $f(\mathcal{Q})$ gravity provides a compelling alternative to standard cosmic models and provides deep insights into the nature of gravitational interaction and the early cosmos.

gr-qc↗

arXiv2024

Study of Cosmic Evolution admitting Thermodynamic Analysis

This article examines the cosmic evolution in the framework of symmetric teleparallel theory, characterized by the function of non-metricity scalar $(\mathcal{Q})$. We use the e-folding number and reconstruction method with a suitable parametrization of the scale factor to obtain the functional form of symmetric teleparallel theory. Using this reconstructed model, we examine the behavior of different cosmographic parameters to demonstrate the bouncing scenarios of the cosmos by considering the contraction and expansion phases of cosmos before and after the bouncing point, respectively. It is found that the null energy condition is violated which shows that the singularity issue can be resolved in this extended theoretical framework. Moreover, we observe that the acceleration occurs near the bouncing point and the reconstructed model aligns with the current cosmic expansion. Finally, we check the validity of second law of thermodynamics in the bouncing framework of our model.

gr-qc↗

arXiv2024

Analysis of Bouncing Cosmology in Non-Riemannian Geometry

The main objective of this manuscript is to investigate the bouncing cosmology in the background of $f(\mathcal{Q})$ gravity, where $\mathcal{Q}$ defines the non-metricity. For this purpose, we use the reconstruction approach and consider a flat Friedmann-Robertson-Walker spacetime with perfect matter configuration. We examine how the first contracting phase gives the expansion by using a temporal derivative of the scale factor, i.e., $\dot{a}<0$, $\dot{a}=0$ and $\dot{a}>0$ give contraction, bounce point and expansion phases, respectively. Further, we use the order reduction method to solve the modified field equations as these are very difficult due to the presence of additional non-linear expressions. It is analyzed that the original singularity of the universe diminishes for the required bounce conditions. We conclude that the acceleration occurs near the bouncing point and the considered $f(\mathcal{Q})$ models are consistent with the current cosmic accelerated expansion.

gr-qc↗