Finite-Temperature Form Factors: a Review

TL;DR

This review discusses finite-temperature form factors in integrable quantum field theory, highlighting their construction, properties, and application to correlation functions in models like the quantum Ising model.

Contribution

It introduces the twisted construction of finite-temperature form factors, extending previous work and enabling new calculations in the quantum Ising model.

Findings

Development of the full construction of finite-temperature form factors for the massive Majorana theory

Application of the framework to compute correlation functions in the quantum Ising model

Introduction of the twisted construction essential for quantum Ising model analysis

Abstract

We review the concept of finite-temperature form factor that was introduced recently by the author in the context of the Majorana theory. Finite-temperature form factors can be used to obtain spectral decompositions of finite-temperature correlation functions in a way that mimics the form-factor expansion of the zero temperature case. We develop the concept in the general factorised scattering set-up of integrable quantum field theory, list certain expected properties and present the full construction in the case of the massive Majorana theory, including how it can be applied to the calculation of correlation functions in the quantum Ising model. In particular, we include the ''twisted construction'', which was not developed before and which is essential for the application to the quantum Ising model.