Cosmology in General Massive Gravity Theories
  We study the cosmology of general massive gravity theories with five
propagating degrees of freedom. This large class of theories includes both the
case with a residual Lorentz invariance as the cases with simpler rotational
invariance. We find that the existence of a nontrivial homogeneous FRW
background, in addition to selecting the lorentz-breaking case, implies in
general that perturbations around strict Minkowski or dS space are strongly
coupled. The result is that dark energy can be naturally accounted for in
massive gravity but its equation of state w_eff has to deviate from -1. We find
indeed a relation between the strong coupling scale of perturbations and the
deviation of w_eff from -1. Taking into account current limits on w_eff and
submillimiter tests of the Newton's law as a limit on the possible strong
coupling regime, we find that it is still possible to have a weakly coupled
theory in a quasi dS background. Future experimental improvements may be used
to predict w_eff in a weakly coupled massive gravity theory
