Kinetic Coupling Corrected Einstein-Gauss-Bonnet Gravity Late-Time Phenomenology

TL;DR

This paper explores a scalar-tensor gravity model with kinetic coupling, demonstrating its potential to match observational data and behave consistently with known cosmological constraints, including late-time acceleration and gravitational wave speed.

Contribution

It introduces a kinetic coupling corrected Einstein-Gauss-Bonnet model with specific $f(R)$ forms, analyzing its late-time cosmological viability and compatibility with observations.

Findings

Models fit Planck data and resemble $ ext{Λ}$CDM.

Tensor perturbation speed equals unity across studied redshifts.

Dark energy oscillations occur in power-law $f(R)$ models.

Abstract

In this short note we present the dynamics of a general scalar-tensor model, and in particular a scalar Einstein-Gauss-Bonnet model with a non-minimal coupling between gravity and the kinetic term of the scalar field. For the sake of simplicity two $f(R)$ models are studied separately, an exponential and a power-law, accompanied by either an exponential or quartic scalar potential and a strictly exponential Gauss-Bonnet scalar coupling function known for being a suitable candidate for describing both the early and the late time. By introducing the general framework of a late-time study for an arbitrary scalar-tensor model, we find that the aforementioned models are capable of producing compatible with the Planck data observations and are in a relatively good agreement with the $\Lambda$CDM model and the GW170817 event as the tensor perturbation velocity is equal to unity in natural units for the whole are of values of redshift studied if certain parameters are properly designated. A brief comment on the appearance of dark energy oscillations which appear for the case of power-law $f(R)$ and the overall viability of the model is also made.