Abstract
Gauss–Bonnet-dilatonic coupling in four dimensions plays an important role to explain late-time cosmic evolution. However, this term is an outcome of the low energy string effective action and thus ought to be important in the early universe too. Unfortunately, a phase-space formulation of such a theory does not exist in the literature due to branching. We therefore consider a modified theory of gravity, which contains a nonminimally coupled scalar–tensor sector in addition to a higher-order scalar curvature invariant term with Gauss–Bonnet-dilatonic coupling. Such an action unifies early inflation with late-time cosmic acceleration. The quantum version of the theory is also well behaved.
Highlights
A smooth luminosity-distance versus redshift curve reveals that distant supernovae appear dimmer than usual [1,2]
The problem of branching, which appeared due to the presence of a higher degree term in the action (8) has been bypassed by the introduction of a higher-order curvature invariant term—R2
Any higher-order curvature invariant term can cure the problem associated with a higher degree, but as Rμν Rμν leads to a ghost, it is safe to handle the situation, with a scalar curvature invariant term
Summary
A smooth luminosity-distance versus redshift curve reveals that distant supernovae appear dimmer than usual [1,2]. Important issues like late-time dominance of dark energy after a scaling matter era, alleviating the coincidence problem crossing the phantom divide line, and compatibility with the observed spectrum of cosmic background radiation have been addressed recently [58,59,60,61]. It gives fruitful results in a Noether symmetry study as well [62]. It appears that the action (7) is a better option to demonstrate the evolutionary history of the universe
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