Unification of a bounce with a viable dark energy era in Gauss-Bonnet gravity

In this work we demonstrate that it is possible to describe a primordial bounce with the dark energy era in a unified way, in the context of Gauss-Bonnet modified gravity. In particular, the early-time bounce has a nearly scale-invariant power spectrum of primordial scalar curvature perturbations, while the dark energy era is a viable one, meaning that it mimics the. cold dark matter model and is also compatible with the Planck 2018 data on cosmological parameters. In addition, our analysis indicates that the dark energy era is free from dark energy oscillations, which occur in the context of f(R) gravity. We further address the latter issue by examining f(R) extensions of Gauss-Bonnet models, and we show that the f(R) gravity part of the action actually produces the dark energy oscillations at redshifts z similar to 4.