Quantum field theoretic properties of Lorentz-violating operators of   nonrenormalizable dimension in the fermion sector
  In the current paper the properties of a quantum field theory based on certain sets of Lorentz-violating coefficients in the nonminimal fermion sector of the Standard-Model Extension are analyzed. In particular, three families of coefficients are considered, where two of them are CPT-even and the third is CPT-odd. As a first step the modified fermion dispersion relations are obtained. Then the positive- and negative-energy solutions of the modified Dirac equation and the fermion propagator are derived. These are used to demonstrate the validity of the optical theorem at tree-level, which provides a cross-check for the results obtained. Furthermore unitarity is examined and seems to be valid for the first set of CPT-even coefficients. However for the remaining sets certain issues with unitarity are found. The article demonstrates that the adapted quantum field theoretical methods at tree-level work for the nonminimal, Lorentz-violating framework considered. Besides, the quantum field theory based on the first family of CPT-even coefficients is most likely well-behaved at lowest order perturbation theory. The results are important for future phenomenological investigations carried out in the context of field theory, e.g., the computation of decay rates and cross sections at tree-level. 
M. Schreck
hep-th