Constraints on dark energy models from the Horndeski theory

TL;DR

This paper explores constraints on dark energy models within the Horndeski gravity framework, emphasizing the roles of scalar field self-interactions and couplings, and assessing their compatibility with cosmological observations and gravitational wave data.

Contribution

It introduces specific exponential self-interaction and coupling functions in Horndeski theory and analyzes their impact on cosmic evolution and observational constraints.

Findings

Derivative self-interaction influences late-time universe dynamics.

Derivative coupling dominates during radiation era but diminishes today.

Gravitational wave speed and dark energy equation of state are consistent with observations.

Abstract

In light of the cosmological observations, we investigate dark energy models from the Horndeski theory of gravity. In particular, we consider cosmological models with the derivative self-interaction of the scalar field and the derivative coupling between the scalar field and gravity. We choose the self-interaction term to have an exponential function of the scalar field with both positive and negative exponents. For the function that has a positive exponent, our result shows that the derivative self-interaction term plays an important role in the late-time universe. On the other hand, to reproduce the right cosmic history, the derivative coupling between the scalar field and gravity must dominate during the radiation-dominated phase. However, the importance of such a coupling in the present universe found to be negligible due to its drastic decrease over time. Moreover, the propagation speed of gravitational waves estimated for our model is within the observational bounds, and our model satisfies the observational constraints on the dark energy equation of state.