Constraints on Gauss-Bonnet Gravity in Dark Energy Cosmologies

TL;DR

This paper investigates how scalar fields coupled to the Gauss-Bonnet term influence cosmological perturbations and uses observational data to constrain their contribution to dark energy.

Contribution

It derives simple expressions for key cosmological observables in Gauss-Bonnet gravity models and provides the first observational constraint on the Gauss-Bonnet energy fraction in dark energy.

Findings

Gauss-Bonnet energy fraction cannot exceed 15%

Derived expressions for anisotropic stress, gravitational constant, and matter growth

Future observations could further constrain Gauss-Bonnet effects

Abstract

Models with a scalar field coupled to the Gauss-Bonnet Lagrangian appear naturally from Kaluza-Klein compactifications of pure higher-dimensional gravity. We study linear, cosmological perturbations in the limits of weak coupling and slow-roll, and derive simple expressions for the main observable sub-horizon quantities: the anisotropic stress factor, the time-dependent gravitational constant, and the matter perturbation growth factor. Using present observational data, and assuming slow-roll for the dark energy field, we find that the fraction of energy density associated with the coupled Gauss-Bonnet term cannot exceed 15%. The bound should be treated with caution, as there are significant uncertainies in the data used to obtain it. Even so, it indicates that the future prospects for constraining the coupled Gauss-Bonnet term with cosmological observations are encouraging.