Cosmological solutions in $f(Q)$ gravity via Noether symmetry approach

TL;DR

This paper uses Noether symmetry to derive exact cosmological solutions in $f(Q)$ gravity within FRW spacetime. The authors obtain the analytic form $f(Q)=c(Q-nQ)^{\frac{3}{2-2n}}$, leading to a power-law expansion $a(t)\propto t^{\frac{1}{1-n}}$ that accelerates for $n<1$, and they analyze the resulting dynamics via a dynamical-systems approach, identifying fixed points corresponding to different cosmic epochs. They further extend the analysis to a $f(Q)$ scalar-tensor cosmology, deriving the Noether charges and constraints that govern the coupled system. The results provide a symmetry-guided pathway to viable cosmological models in non-metricity gravity and offer a bridge to observational viability through inflationary diagnostics and epochal dynamics.

Abstract

Symmetry plays a crucial role in theoretical physics, especially Noether symmetry, which is a powerful approach for identifying the models at the fundamental level. The exact solution is provided within the point-like Lagrangian framework. In this work, we study one of the alternative theories of gravity based on the non-metricity scalar $Q$, namely $f(Q)$ gravity, via Noether symmetry. We utilize Noether symmetry within the framework of $f(Q)$ gravity to derive the functional expression for $f(Q)$, which is given by $f(Q)=c(Q-nQ)^{\frac{3}{2-2n}}$. To confirm the exact solution of the model through Noether symmetry, we continue to consider the Friedmann-Robertson-Walker (FRW) cosmology with the dynamical solution of the system using dimensionless variables and show that the accelerated expansion of the universe follows a power law scale factor. In the following, we show that the quantities corresponding to the exact solution for $n<1$ lead to an accelerated expansion universe. Finally, in the framework of $f(Q)$ scalar-tensor cosmology, we apply the Noether symmetry approach to find the cosmological models consistent with the Noether symmetry.

Figures (1)

• Figure 1: A phase portrait of $\Lambda$CDM, radiation-dominated, and matter-dominated universe from left to right, respectively.