Cosmic expansion and growth histories in Galileon scalar-tensor models of dark energy

TL;DR

This paper investigates Galileon scalar-tensor models for dark energy, showing they mimic standard cosmological expansion but differ in the universe's fate and matter perturbation growth, with potential observational signatures.

Contribution

It introduces non-linear derivative interactions in scalar-tensor theories, demonstrating their effects on cosmic expansion and structure growth, and distinguishes these models from standard dark energy.

Findings

Expansion history closely matches $\\Lambda$CDM and dark energy models.

Growth index varies from 9/16 in the past to as low as 0.4 today.

Universe's fate depends on model parameters.

Abstract

We study models of late-time cosmic acceleration in terms of scalar-tensor theories generalized to include a certain class of non-linear derivative interaction of the scalar field. The non-linear effect suppress the scalar-mediated force at short distances to pass solar-system tests of gravity. It is found that the expansion history until today is almost indistinguishable from that of the $\Lambda$CDM model or some (phantom) dark energy models, but the fate of the universe depends clearly on the model parameter. The growth index of matter density perturbations is computed to show that its past asymptotic value is given by 9/16, while the value today is as small as 0.4.