1202.3131 (Nathalie Deruelle et al.)

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

Nathalie Deruelle, Misao Sasaki, Yuuiti Sendouda, Ahmed Youssef

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. Such a behaviour is in sharp contrast to what happens in
standard Weyl gravity where the gravitational ghosts smoothly damp out the
spectrum of primordial gravitational waves.

View original: http://arxiv.org/abs/1202.3131