Noncausal effects in relativistic wave equations

The problem of determining whether a given type of external field interaction will lead to noncausal wave propagation in the context of the five-component Duffin-Kemmer-Petiau (DKP) spin-0 theory is considered. It is shown that if a Peirce decomposition of the DKP spin-0 equation is applied for each of the couplings in the equation, the causal properties become apparent from the form of the operator H in the resulting Schroedinger-type equation.