Relativistically covariant chronological ordering of interaction lagrangians

A general form of chronological ordering is proposed, based on introduction of relativistically invariant multipoint step functions τ(x1, ..., xn). A system of recursive relations is established for these functions, which guarantees that the scattering matrix is unitary, covariant, and causal. The explicit form of the first four τ-functions is found. A comparative analysis of the known methods of chronological ordering is given. © 1990 Plenum Publishing Corporation.