Antonio De Felice, A. Emir Gumrukcuoglu, Shinji Mukohyama
We study the propagating modes for nonlinear massive gravity on a Bianchi type--I manifold. We analyze their kinetic terms and dispersion relations as the background manifold approaches the homogeneous and isotropic limit. We show that in this limit, at least one ghost always exists and that its frequency tends to vanish for large scales, meaning that it cannot be integrated out from the low energy effective theory. Since this ghost mode can be considered as a leading nonlinear perturbation around a homogeneous and isotropic background, we conclude that the universe in this theory must be either inhomogeneous or anisotropic.
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http://arxiv.org/abs/1206.2080
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