Finite temperature correlation functions from form factors

TL;DR

This paper examines extending the form factor approach for calculating correlation functions from zero to finite temperature, finding it suitable only for free theories and highlighting the need for significant modifications in interacting theories.

Contribution

It clarifies the limitations of current form factor methods at finite temperature and emphasizes the necessity for new approaches in interacting quantum field theories.

Findings

Form factor expansion with dressing functions works for free theories.

Interacting theories require substantial modifications to the form factor approach.

Current proposals are inadequate for dynamical interactions at finite temperature.

Abstract

We investigate proposals of how the form factor approach to compute correlation functions at zero temperature can be extended to finite temperature. For the two-point correlation function we conclude that the suggestion to use the usual form factor expansion with the modification of introducing dressing functions of various kinds is only suitable for free theories. Dynamically interacting theories require a more severe change of the form factor program.