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

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

2007-02-01

arxiv.org/abs/hep-th/0702002v2

JCAP 0705:019,2007

Physics

High Energy Physics

High Energy Physics - Theory

44 pages, several eps figures; section 2 expanded with discussions on cosmological/astrophysical constraints, final in JCAP

Scientific paper

10.1088/1475-7516/2007/05/019

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 $\phi$ 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.

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