Abstract
Models with a scalar field coupled to the Gauss–Bonnet Lagrangian appear naturally fromKaluza–Klein compactifications of pure higher-dimensional gravity. We studylinear, cosmological perturbations in the limits of weak coupling and slow-roll, andderive simple expressions for the main observable sub-horizon quantities: theanisotropic stress factor, the time-dependent gravitational constant, and the matterperturbation growth factor. Using present observational data, and assuming slow-rollfor the dark energy field, we find that the fraction of energy density associatedwith the coupled Gauss–Bonnet term cannot exceed 15%. The bound should betreated with caution, as there are significant uncertainties in the data used toobtain it. Even so, it indicates that the future prospects for constraining thecoupled Gauss–Bonnet term with cosmological observations are encouraging.
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