Lorentz violation and higher-derivative gravity

Understand

In this work, we analyze a gravity model with higher derivatives including a CPT-even Lorentz-violating term.

• In principle, the model could be a low-energy limit of a Lorentz-invariant theory presenting the violation of Lorentz symmetry as a consequence of a spontaneous symmetry-breaking mechanism if a decoupling between the metric and the Nambu-Goldstone modes is assumed.
• We have set up a convenient operator basis for the expansion of wave operators for symmetric second-rank tensors in the presence of a background vector.
• By using this set of operators, the particle content is obtained, and its consistency, regarding the conditions for stability and unitarity, is discussed.