  (Anti)causal boundary conditions being imposed on the (seemingly) Hermitian
Quantum Theory (HQT) as described in standard textbooks lead to an (Anti)Causal
Quantum Theory ((A)CQT) with an indefinite metric. Therefore, an (anti)causal
neutral scalar field is not Hermitian, as one (anti)causal neutral scalar field
consists of a non-Hermitian linear combination of two (Hermitian) acausal
fields. Fundamental symmetries in (A)CQT are addressed. The quantum theoretical
(transition) probability and antiparticle concepts are revised. Imaginary parts
of cross sections and refraction indices are related.
