Lorentz Breaking Massive Gravity in Curved Space
  A systematic study of the different phases of Lorentz-breaking massive
gravity in a curved background is performed. For tensor and vector modes, the
analysis is very close to that of Minkowski space. The most interesting results
are in the scalar sector where, generically, there are two propagating degrees
of freedom (DOF). While in maximally symmetric spaces ghost-like instabilities
are inevitable, they can be avoided in a FRW background. The phases with less
than two DOF in the scalar sector are also studied. Curvature allows an
interesting interplay with the mass parameters; in particular, we have extended
the Higuchi bound of dS to FRW and Lorentz breaking masses. As in dS, when the
bound is saturated there is no propagating DOF in the scalar sector. In a
number of phases the smallness of the kinetic terms gives rise to strongly
coupled scalar modes at low energies. Finally, we have computed the
gravitational potentials for point-like sources. In the general case we recover
the GR predictions at small distances, whereas the modifications appear at
distances of the order of the characteristic mass scale. In contrast with
Minkowski space, these corrections may not spoil the linear approximation at
large distances.
