Gravitational Cherenkov Radiation from Extended Theories of Gravity
  We linearize the field equations for higher order theories of gravity that contain scalar invariants other than the Ricci scalar. We find that besides a massless spin-2 field (the standard graviton), the theory contains also spin-0 and spin-2 massive modes with the latter being, in general, ghost modes. The rate at which such particles would emit gravitational Cherenkov radiation is calculated for some interesting physical cases. 
M. De Laurentis, S. Capozziello, G. Basini
gr-qc astro-ph.HE hep-th