Consistency of Relevant Cosmological Deformations on all Scales
  Using cosmological perturbation theory we show that the most relevant defor- mation of gravity is consistent at the linear level. In particular, we prove the absence of uni- tarity violating negative norm states in the weak coupling regime from sub- to super-Hubble scales. This demonstrates that the recently proposed classical self-protection mechanism of deformed gravity extends to the entire kinematical domain. 
Felix Berkhahn, Dennis D. Dietrich, Stefan Hofmann
hep-th astro-ph.CO gr-qc