  Bigravity is one of the natural extensions of general relativity and contains
an additional massive spin-2 field which can be a good candidate for dark
matter. To discuss the production of spin-2 dark matter, we study fixed point
solutions of the background equations for axisymmetric Bianchi type-I Universes
in two bigravity theories without Boulware-Deser ghost, i.e., Hassan-Rosen
bigravity and Minimal Theory of Bigravity. We investigate the local and global
stability of the fixed points and classify them. Based on the general analysis,
we propose a new scenario where spin-2 dark matter is produced by the
transition from an anisotropic fixed point solution to isotropic one. The
produced spin-2 dark matter can account for all or a part of dark matter and
can be directly detected by laser interferometers in the same way as
gravitational waves.
