Cosmology of a covariant Galileon field
  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.
