On Cosmic No-hair in Bimetric Gravity and the Higuchi Bound
  We study the cosmic no-hair in the presence of spin-2 matter, i.e. in
bimetric gravity. We obtain stable de Sitter solutions with the cosmological
constant in the physical sector and find an evidence that the cosmic no-hair is
correct. In the presence of the other cosmological constant, there are two
branches of de Sitter solutions. Under anisotropic perturbations, one of them
is always stable and there is no violation of the cosmic no-hair at the linear
level. The stability of the other branch depends on parameters and the cosmic
no-hair can be violated in general. Remarkably, the bifurcation point of two
branches exactly coincides with the Higuchi bound. It turns out that there
exists a de Sitter solution for which the cosmic no-hair holds at the linear
level and the effective mass for the anisotropic perturbations is above the
Higuchi bound.
