Generalized dark gravity
  The late-time cosmic acceleration may be due to infra-red modifications of
General Relativity. In particular, we consider a maximal extension of the
Hilbert-Einstein action and analyze several interesting features of the theory.
Generally, the motion is non-geodesic and takes place in the presence of an
extra force, which is orthogonal to the four-velocity. These models could lead
to some major differences, as compared to the predictions of General Relativity
or other modified theories of gravity, in several problems of current interest,
such as cosmology, gravitational collapse or the generation of gravitational
waves. The study of these phenomena may also provide some specific signatures
and effects, which could distinguish and discriminate between the various
gravitational models.
