Gauss–Bonnet cosmologies: crossing the phantom divide and the transition from matter dominance to dark energy

Abstract

Dark energy cosmologies with an equation of state parameter w less than −1 are often found to violate the null energy condition and show unstable behaviour. A solution to this problem may require the existence of a consistent effective theory that violates the null energy condition only momentarily and does not develop any instabilities or other pathological features for a late time cosmology. A model which incorporates a dynamical scalar field ϕ coupled to the quadratic Riemann invariant of the Gauss-Bonnet form is a viable proposal. Such an effective theory is shown to admit nonsingular cosmological evolutions for a wide range of scalar-Gauss-Bonnet coupling. We discuss the conditions for which our model yields observationally supported spectra of scalar and tensor fluctuations, under cosmological perturbations. The model can provide a reasonable explanation for the transition from matter dominance to dark energy regime and the late time cosmic acceleration, offering an interesting testing ground for investigations of the cosmological modified gravity.

Energy conditions in modified f(G) gravity

“…There has been an interested results found on the exploration of dark source terms on the dynamical evolution of stellar systems in Einstein-Λ [26], f (R) [27], f (R, T ) [28] (T is the trace of energy momentum tensor) and f (R, T, R µν T µν ) gravity [29]. Among MGTs, available in the literature, the one is Gauss Bonnet (GB) gravity which has received great attraction [30][31][32][33][34][35][36][37][38][39][40] and is named as f (G) gravity, where…”

“…The equation of motion for this gravity is required to be coupled with some scalar field or f (G) must be some arbitrary function of G. This MGT could help out in the study of inflationary era, transition of acceleration from deceleration regimes, passing tests induced by solar system experiments and crossing phantom divide line for different viable f (G) models [32,33]. It is also seen that the GB gravity is less constrained than f (R) gravity [34].…”

Some exact solutions with torsion in 5D Einstein-Gauss-Bonnet gravity

“…an incomplete list of references, [5,6,7,8,9,10,11,12,13,14,15,16]). The addition of Lovelock terms to the action affects the equations of motion in such a way that they no longer imply that the torsion vanishes.…”

Inflation and quintessence: theoretical approach of cosmological reconstruction

“…pressureless dust (w m = 0), radiation (w r = 1/3), stiff matter (w sm = 1), domain walls (w dw = −2/3), etc. For further analysis, it is useful to introduce the so called effective equation of state parameter w eff , which is defined by 27) whereas p Q and ρ Q are as defined in eq. (3.16), and …”