Cosmologies of extended massive gravity
  We study the background cosmology of two extensions of dRGT massive gravity.
The first is variable mass massive gravity, where the fixed graviton mass of
dRGT is replaced by the expectation value of a scalar field. We ask whether
self-inflation can be driven by the self-accelerated branch of this theory, and
we find that, while such solutions can exist for a short period, they cannot be
sustained for a cosmologically useful time. Furthermore, we demonstrate that
there generally exist future curvature singularities of the "big brake" form in
cosmological solutions to these theories. The second extension is the covariant
coupling of galileons to massive gravity. We find that, as in pure dRGT
gravity, flat FRW solutions do not exist. Open FRW solutions do exist -- they
consist of a branch of self-accelerating solutions that are identical to those
of dRGT, and a new second branch of solutions which do not appear in dRGT.
