The Fate of the Universe Evolution in the Quadratic Form of Ricci–Gauss–Bonnet Cosmology

We investigate the possibility of a future singularity due to accelerating expansion of the Universe in a gravitational theory that comprises the Ricci scalar \(R\) and the Gauss–Bonnet invariant \(\mathcal{G}\), known as \(F(R,\mathcal{G})\) gravity, which can be viewed in the quadratic form. Three models are presented using Hubble parameters to represent a finite and infinite future. The model parameters are analyzed on the basis of their physical and geometrical properties. This study also explores the properties of the modified gravitational theory, and neither a future singularity nor a little or pseudo-rip are posed as threats to the fate of the Universe. We present scalar perturbation approaches to perturbed evolution equations and demonstrate their stability.