On covariant perturbations with scalar field in modified Gauss–Bonnet gravity

Abstract

We investigate cosmological perturbations of f (G) gravity in the presence of a scalar field. Using the 1 + 3 covariant formalism, we present the energy over density perturbation equations responsible for large scale structure formation. After applying harmonic decomposition method together with the redshift transformation technique, we obtain the fully perturbed equations in redshift space. The equations are solved to study the growth of matter over densities contrast with redshift. For both short- and long wave length modes, we obtain numerical results for particular functional form f (G) models and scalar field. We find that, for this choice the energy over density perturbations decay with increase in redshift. However, for both short- and long wavelength modes, the perturbations which include amplitude effects due to the f (G) models with a scalar field do differ remarkably from those in ^CDM. The results reduce to GR results in the limit of f (G) → G and in the absence of scalar field.