Scalar-Gauss-Bonnet model, the coincidence problem and the gravitational wave speed

TL;DR

This paper proposes a dynamical dark energy model involving quintessence interacting with the Gauss-Bonnet invariant and dark matter, explaining the emergence of dark energy during cosmic evolution while maintaining consistency with gravitational wave speed constraints.

Contribution

It introduces a novel interaction mechanism between quintessence, the Gauss-Bonnet invariant, and dark matter that accounts for dark energy's evolution without affecting late-time cosmic dynamics.

Findings

Dark energy remains negligible during radiation era

Dark energy emerges during matter era due to conformal coupling

Model consistent with gravitational wave speed constraints

Abstract

We introduce a dynamical dark energy model wherein quintessence interacts with both the Gauss-Bonnet invariant and dark matter. Initially, the Gauss-Bonnet invariant stabilizes the quintessence at a fixed point, resulting in a negligible density of dark energy. Subsequently, the conformal coupling to dark matter triggers the evolution of dark energy. This model proposes an explanation for the initial absence of dark energy in radiation era and its later emergence during the matter-dominated era, achieving a magnitude comparable to dark matter in the present epoch. In this scenario, the Gauss-Bonnet term does not directly influence late-time cosmic evolution. Our model aligns with the assumption that the speed of gravitational wave is infinitesimally close to the speed of light.