Bouncing cosmologies and stability analysis in symmetric teleparallel $f(Q)$ gravity

TL;DR

This paper explores bouncing cosmological models within symmetric teleparallel $f(Q)$ gravity, analyzing stability, cosmological parameters, and perturbations, and finds that the model exhibits mostly stable behavior with the EoS parameter crossing the phantom divide near the bounce.

Contribution

It introduces a specific $f(Q)$ gravity model with a chosen scale factor to realize a bouncing universe and analyzes its stability and physical viability.

Findings

The model exhibits mostly stable behavior over cosmic time.

The EoS parameter crosses the phantom divide near the bounce.

The exact solutions support a physically consistent bouncing scenario.

Abstract

This paper is devoted to examining cosmological bouncing scenarios in the framework of the recently proposed symmetric teleparallel gravity (or $f(Q)$ gravity), where the non-metricity scalar $Q$ represents the gravitational interaction. We assume an $f(Q)$ model in the form of $f(Q)=\alpha Q^n$, where $\alpha$ and $n$ are free model parameters. To obtain a bouncing universe, we consider a special form of the scale factor $a(t)$ in terms of cosmic time, specifically $a(t) = (1+\lambda t^2)^{1/3}$, where $\lambda$ is an arbitrary constant. We derive the field equations for the flat FLRW universe and obtain the corresponding exact solution. We investigate the physical behavior of various cosmological parameters such as the deceleration parameter, pressure, and equation of state (EoS) parameter with the energy conditions for our bounce cosmological model. Furthermore, we investigate the behavior of the perturbation terms $\delta_m(t)$ and $\delta(t)$ with respect to cosmic time $t$ using the scalar perturbation approach. We found that although the model exhibits unstable behavior at the beginning for a brief period, it shows mostly stable behavior for most of the time. Finally, we conclude that the EoS parameter crosses the quintom line $\omega=-1$ in the vicinity of the bouncing point $t=0$, which confirms the success of our bounce cosmological model.