$G_{3}$ -- interacting scalar tensor dark energy

TL;DR

This paper explores an interacting scalar-tensor dark energy model within Horndeski theory, analyzing its stability, background evolution, and perturbations, and tests it against cosmological data using genetic algorithms.

Contribution

It introduces a specific interaction in the $G_3$ term of Horndeski theory, derives stability conditions, and employs genetic algorithms to fit the model to observational data.

Findings

Modified gravitational couplings to matter densities.

Consistent background and perturbation evolution with observational data.

Model viability tested against $H(z)$ and $f\sigma_8$ data.

Abstract

We study the effect of adding an interaction in the $G_3$ term of Horndeski theory, where the propagation of gravitational waves are not modified. We derive the background and perturbation equations of motion from the action. We also derive the no-ghost and Laplacian instability conditions for tensor modes and scalar mode propagation. Then we study the evolution of the matter perturbation in the quasi-static approximation. We find that the gravitational couplings to the baryonic and cold dark matter over density are modified in this theory. We introduce a concrete model of the free function in the theory and study the background and linear perturbation dynamics. We then use the genetic algorithm to test the model. We compare the $H(z)$ function of the model and the $H(z)$ curve predicted by the genetic algorithm, using the $H(z)$ data. For the perturbation sector we compute the $f\sigma_{8}$ observable for the model and compare it with the predicted function from the genetic algorithm from the $f\sigma_{8}$ data.