Causal signal transmission by quantum fields. IV: The causal Wick theorem

TL;DR

This paper reformulates Wick's theorem within the Schwinger-Perel-Keldysh formalism, showing that it encodes the propagation of free quantum fields through the linear response function, clarifying the causal structure of quantum field interactions.

Contribution

It introduces a causal version of Wick's theorem where contractions are replaced by the linear response function, highlighting the causal propagation of quantum fields.

Findings

Wick's theorem expressed via the linear response function.

Clarification of the causal structure in quantum field propagation.

Demonstration that operator information relates to free field propagation.

Abstract

Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism is written in a form where the place of contractions is taken by the linear response function of the field. This result demonstrates that the physical information supplied by Wick's theorem for operators is propagation of the free field in space and time.