Dynamical system analysis of scalar field cosmology in coincident $f(Q)$ gravity

TL;DR

This paper analyzes scalar field cosmology within coincident $f(Q)$ gravity, exploring phase-space dynamics, stability, and universe evolution, comparing exponential and power-law potentials, and identifying conditions for accelerated expansion.

Contribution

It introduces a polynomial $f(Q)$ model with specific scalar potentials, analyzing the stability and cosmological implications in a unified phase-space framework.

Findings

Exponential potential leads to universe evolution from stiff to de-Sitter era.

Power-law potential also shows transition from stiff to de-Sitter era.

Exponential case provides better cosmological evolution results.

Abstract

In this article, we investigate scalar field cosmology in the coincident $f(Q)$ gravity formalism. We calculate the motion equations of $f(Q)$ gravity under the flat Friedmann-Lema\^{i}tre-Robertson-Walker background in the presence of a scalar field. We consider a non-linear $f(Q)$ model, particularly $f(Q)=-Q+\alpha Q^n$, which is nothing but a polynomial correction to the STEGR case. Further, we assumed two well-known specific forms of the potential function, specifically the exponential from $V(\phi)= V_0 e^{-\beta \phi}$ and the power-law form $V(\phi)= V_0\phi^{-k}$. We employ some phase-space variables and transform the cosmological field equations into an autonomous system. We calculate the critical points of the corresponding autonomous systems and examine their stability behaviors. We discuss the physical significance corresponding to the exponential case for parameter values $n=2$ and $n=-1$ with $\beta=1$, and $n=-1$ with $\beta=\sqrt{3}$. Moreover, we discuss the same corresponding to the power-law case for the parameter value $n=-2$ and $k=0.16$. We also analyze the behavior of corresponding cosmological parameters such as scalar field and dark energy density, deceleration, and the effective equation of state parameter. Corresponding to the exponential case, we find that the results obtained for the parameter constraints in Case III is better among all three cases, and that represents the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era via matter-dominated epoch. Further, in the power-law case, we find that all trajectories exhibit identical behavior, representing the evolution of the universe from a decelerated stiff era to an accelerated de-Sitter era. Lastly, we conclude that the exponential case shows better evolution as compared to the power-law case.