What are the properties of the Standard-Model Extension?
The quick answer is that the Standard-Model Extension has all the properties of the usual Standard Model and General Relativity except that Lorentz and CPT symmetry can be violated. In the Standard-Model Extension, even one type of Lorentz symmetry remains valid: the theory transforms normally under rotations or boosts of the observer’s inertial frame (observer Lorentz transformations). The apparent Lorentz violations appear only when the particle fields are rotated or boosted (particle Lorentz transformations) relative to the vacuum tensor expectation values. More technically: the full Standard-Model Extension contains all possible coordinate-invariant operators formed by combining Standard-Model and gravitational fields with couplings having Lorentz indices. For most situations at energies well below the scale of the underlying theory, it suffices to study the subset of the full Standard-Model Extension for which the gauge structure and the power-counting renormalizability of the usu
