Cosmological perturbations in f(G) gravity

Abstract

We explore cosmological perturbations in a modified Gauss–Bonnet [Formula: see text] gravity, using a [Formula: see text] covariant formalism. In such a formalism, we define gradient variables to get perturbed linear evolution equations. We transform these linear evolution equations into ordinary differential equations using a spherical harmonic decomposition method. The obtained ordinary differential equations are time-dependent and then transformed into redshift-dependent. After these transformations, we analyze energy-density perturbations for two fluid systems, namely, for a Gauss–Bonnet field-dust system and for a Gauss–Bonnet field-radiation system for three different pedagogical [Formula: see text] models: trigonometric, exponential and logarithmic. For the Gauss–Bonnet field-dust system, energy-density perturbations decay with increase in redshift for all the three models. For the Gauss–Bonnet field-radiation system, the energy-density perturbations decay with increase in redshift for all of the three [Formula: see text] models for long wavelength modes whereas for short wavelength modes, the energy-density perturbations decay with increasing redshift for the logarithmic and exponential [Formula: see text] models and oscillate with decreasing amplitude for the trigonometric [Formula: see text] model.

Late-time Cosmology of scalar field assisted $f(\mathcal{G})$ gravity

“…While the latter is showcased in the present article, a thorough study of tensor perturbations is a quite challenging topic and is thus not available, in principle however tensor perturbations should be quite similar to Ref. [57]. The important aspect that is worth being highlighted is that the models at hand are free of ghost instabilities given that the Ricci scalar appears in a linear form.…”

Multifluid cosmology in f(G) gravity

“…The harmonic decomposition technique is used in such a way that the evolution equations can be converted into ordinary differential equations for each mode [19,22,25,26,27]. On an almost FRW space-time, we consider the differential equation of the form…”

“…The 1 + 3 covariant linear perturbations theory have been employed to explain cosmic large scale structure formation. In the recent paper [25], we studied cosmological perturbations in f (G) gravity for a two fluid system at linear order using exponential, logarithmic and trigonometric f (G) models. These models have been proposed by [31,32].…”

“…The 1 + 3 covariant formalism is used for studying cosmological perturbations, developed to analyse the evolution of linear perturbations of Friedmann-Robertson-Walker (FRW) models in different theories of gravity. In [25], the evolution of scalar perturbations of FRW was developed for a single barotropic fluid using the 1 + 3 covariant formalism in f (G) gravity focussing on two-fluid systems. The solutions of the perturbation equations on large scale structure showed that the energy density perturbations decay with increase in redshift, implying more structure formation rate today.…”

Constraints on Non-Flat Starobinsky f(R) Dark Energy Model

“…However, it still confronts some unsolved issues, such as the cosmological constant (CC) problem [8]. This CC problem has motivated people to search for various new theories beyond ΛCDM, such as f (G) [9][10][11], scale dependence cosmology [12][13][14], and scalar tensor [15,16] theories. A typical model of such theories is the f (R) gravity theory, in which the Ricci scalar of R in the Einstein-Hilbert action of the standard general relativity (GR) is modified to an arbitrary function of f (R) [17][18][19][20][21][22][23].…”