Self-accelerating solutions in massive gravity on an isotropic reference   metric
  Within the framework of the recently proposed ghost-free massive gravity, a cosmological constant-type self-accelerating solution has been obtained for Minkowski and de Sitter reference metrics. We ease the assumption on the reference metric and find the self-accelerating solution for the reference metric respecting only isotropy, thus considerably extending the range of known solutions. 
Hayato Motohashi and Teruaki Suyama
hep-th astro-ph.CO gr-qc