Cosmology in generalized Proca theories
  We consider a massive vector field with derivative interactions that
propagates only the 3 desired polarizations (besides two tensor polarizations
from gravity) with second-order equations of motion in curved space-time. The
cosmological implications of such generalized Proca theories are investigated
for both the background and the linear perturbation by taking into account the
Lagrangian up to quintic order. In the presence of a matter fluid with a
temporal component of the vector field, we derive the background equations of
motion and show the existence of de Sitter solutions relevant to the late-time
cosmic acceleration. We also obtain conditions for the absence of ghosts and
Laplacian instabilities of tensor, vector, and scalar perturbations in the
small-scale limit. Our results are applied to concrete examples of the general
functions in the theory, which encompass vector Galileons as a specific case.
In such examples, we show that the de Sitter fixed point is always a stable
attractor and study viable parameter spaces in which the no-ghost and stability
conditions are satisfied during the cosmic expansion history.
