Form factor approach to diagonal finite volume matrix elements in Integrable QFT

TL;DR

This paper derives an exact formula for finite volume excited state mean values of local operators in 1+1 dimensional integrable quantum field theories with diagonal scattering, extending the LeClair-Mussardo series.

Contribution

It introduces a generalized form factor expansion for excited states in integrable QFT, expanding the applicability of finite volume calculations.

Findings

Provides an exact formula for excited state mean values

Generalizes the LeClair-Mussardo series to excited states

Enhances understanding of finite volume effects in integrable QFT

Abstract

We derive an exact formula for finite volume excited state mean values of local operators in 1+1 dimensional Integrable QFT with diagonal scattering. Our result is a non-trivial generalization of the LeClair-Mussardo series, which is a form factor expansion for finite size ground state mean values.