Consistency of isotropic modified Maxwell theory: Microcausality and unitarity

Understand

The Lorentz-violating isotropic modified Maxwell theory minimally coupled to standard Dirac theory is characterized by a single real dimensionless parameter which is taken to vanish for the case of the standard (Lorentz-invariant) theory.

• A finite domain of positive and negative values of this Lorentz-violating parameter is determined, in which microcausality and unitarity hold.
• The main focus of this article is on isotropic modified Maxwell theory, but similar results for two anisotropic nonbirefringent cases are presented in the appendices.