Derivation of the fluctuation-dissipation theorem from unitarity

TL;DR

This paper derives the fluctuation-dissipation theorem within thermal field theory using the closed time path formalism, emphasizing the role of unitarity of the S-matrix in the derivation.

Contribution

It provides a novel derivation of the fluctuation-dissipation theorem based on unitarity, connecting fundamental principles to thermal field theory.

Findings

Derivation of the fluctuation-dissipation theorem from unitarity.

Highlights the role of the S-matrix in thermal fluctuations.

Provides a theoretical foundation linking unitarity and thermal response.

Abstract

Using the closed time path formalism in thermal field theory, we give a derivation of the fluctuation-dissipation theorem which is based on the unitarity of the $S$-matrix.