Cosmology of a covariant Galileon field

TL;DR

This paper explores a covariant Galileon scalar field model in cosmology, identifying conditions for stability, a tracker solution leading to cosmic acceleration, and unique observational signatures distinguishing it from Lambda-CDM.

Contribution

It introduces a stable, covariant Galileon model with a tracker solution that causes late-time acceleration and exhibits distinctive observational features.

Findings

Existence of a tracker solution approaching de Sitter space

Conditions for absence of ghosts and instabilities

Phantom-like behavior of the equation of state

Abstract

We study the cosmology of a covariant scalar field respecting a Galilean symmetry in flat space-time. We show the existence of a tracker solution that finally approaches a de Sitter fixed point responsible for cosmic acceleration today. The viable region of model parameters is clarified by deriving conditions under which ghosts and Laplacian instabilities of scalar and tensor perturbations are absent. The field equation of state exhibits a peculiar phantom-like behavior along the tracker, which allows a possibility to observationally distinguish the Galileon gravity from the Lambda-CDM model.