Stable FLRW solutions in Generalized Massive Gravity
  We present exact FLRW solutions in generalized massive gravity where the mass
parameters are naturally promoted to Lorentz-invariant functions of the
Stuckelberg fields. This new dependence relaxes the constraint that would
otherwise prevent massive gravity from possessing exact FLRW solutions. It does
so without the need to introduce additional degrees of freedom. We find
self-accelerating cosmological solutions and show that, with a mild restriction
on the region of phase space, these cosmological solutions exhibit full
stability, i.e. absence of ghosts and gradient instabilities for all the
tensor, vector and scalar modes, for all cosmic time. We perform the full
decoupling limit analysis, including vector degrees of freedom, which can be
used to confirm the existence of an active Vainshtein mechanism about these
solutions.
