CPT and Lorentz Symmetry

Many important symmetries in physics do not hold exactly. If CPT symmetry were violated, this would have important implications; for example, CPT violation in quantum field theory automatically entails violation of Lorentz symmetry as well. The standard model extension provides a general framework for studying the possible breakdown of these symmetries. Work on this subject has accelerated tremendously in the last fifteen years, and there are many new constraints on Lorentz and CPT symmetry breaking.