Unification of a Bounce with a Viable Dark Energy Era in Gauss-Bonnet
  Gravity
  In this work we shall demonstrate that it is possible to describe in a
unified way a primordial bounce with the dark energy era, in the context of
Gauss-Bonnet modified gravity. Particularly, 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
$\Lambda$-Cold-Dark-Matter model and also is 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 addressed the later issue by examining
$f(R)$ extensions of Gauss-Bonnet models, and we showed that the $f(R)$ gravity
part of the action actually produces the dark energy oscillations at redshifts
$z\sim 4$.
