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

@article{Deruelle2012LorentzviolatingVG,
  title={Lorentz-violating vs. ghost gravitons: the example of Weyl gravity},
  author={Nathalie Deruelle and Misao Sasaki and Yuuiti Sendouda and Ahmed Youssef},
  journal={Journal of High Energy Physics},
  year={2012},
  volume={2012},
  pages={1-21}
}
A bstractWe show that the ghost degrees of freedom of Einstein gravity with a Weyl term can be tamed 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… 
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References

SHOWING 1-10 OF 31 REFERENCES
Tensor ghosts in the inflationary cosmology
Theories with curvature squared terms in the action are known to contain ghost modes in general. However, if we regard curvature squared terms as quantum corrections to the original theory, the
Relativistic Quantum Gravity at a Lifshitz Point
We show that the Hořava theory for the completion of General Relativity at UV scales can be interpreted as a gauge fixed Tensor-Vector theory, and it can be extended to an invariant theory under the
Quantum Gravity at a Lifshitz Point
We present a candidate quantum field theory of gravity with dynamical critical exponent equal to $z=3$ in the UV. (As in condensed-matter systems, $z$ measures the degree of anisotropy between space
The Phantom menaced: Constraints on low-energy effective ghosts
It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled
On the extra mode and inconsistency of Hořava gravity
We address the consistency of Hořava's proposal for a theory of quantum gravity from the low-energy perspective. We uncover the additional scalar degree of freedom arising from the explicit breaking
Inflation with a Weyl term, or ghosts at work
In order to assess the role of ghosts in cosmology, we study the evolution of linear cosmological perturbations during inflation when a Weyl term is added to the action. Our main results are that
Theory of cosmological perturbations
Classical gravity with higher derivatives
Inclusion of the four-derivative terms ∫RμνRμν(−g)1/2 and ∫R2(−g)1/2 into the gravitational action gives a class of effectively multimass models of gravity. In addition to the usual massless
Gauge Invariant Cosmological Perturbations
The physical interpretation of perturbations of homogeneous, isotropic cosmological models in the early Universe, when the perturbation is larger than the particle horizon, is clarified by defining a
f(R) Theories
TLDR
Various applications of f(R) theories to cosmology and gravity — such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds are reviewed.
...
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