Form factor expansion for thermal correlators

Abstract

We consider finite temperature correlation functions in massive integrable quantum fieldtheory. Using a regularization by putting the system in finite volume, we develop a novelapproach (based on multi-dimensional residues) to the form factor expansionfor thermal correlators. The first few terms are obtained explicitly in theorieswith diagonal scattering. We also discuss the validity of the LeClair–Mussardoproposal.