Lorentz-Invariance Violation with Higher-Order Operators
  In this work, in the light of the developments for indefinite metric theories made by Lee and Wick, we study perturbative unitarity in a Lorentz-invariance violating QED model with higher-order operators. We show that by following the Lee-Wick prescription it is possible to preserve unitarity in the model at one-loop order in the coupling. 
Carlos M. Reyes and Luis F. Urrutia
hep-ph