Lorentz-violating vs ghost gravitons: the example of Weyl gravity

Understand

We show that the ghost degrees of freedom of Einstein gravity with a Weyl term can be eliminated by a simple mechanism that invokes local Lorentz symmetry breaking.

• We demonstrate how the mechanism works in a cosmological setting.
• The presence of the Weyl term forces a redefinition of the quantum vacuum state of the tensor perturbations.
• As a consequence the amplitude of their spectrum blows up when the Lorentz-violating scale becomes comparable to the Hubble radius.