C, P and T in relativistic quantum theories
In describing symmetries in relativistic quantum theories we usually start out by showing how relativistic extensions of the Schrödinger equation like the Klein–Gordon and Dirac equations transform under the symmetry; subsequently we discuss quantum field theory. We do not feel that following the historical development is always the most illuminating way to introduce new concepts. Instead we will begin with quantum field theories, i.e. second quantized theory, and subsequently come back to the first quantized version.
To introduce symmetries in quantum field theory, we assume that there are operators which transform states in a way that leave all physical observables unchanged.
In particular, we formulate ...