Mean values of local operators in highly excited Bethe states

Understand

We consider expectation values of local operators in (continuum) integrable models in a situation when the mean value is calculated in a single Bethe state with a large number of particles.

• We develop a form factor expansion for the thermodynamic limit of the mean value, which applies whenever the distribution of Bethe roots is given by smooth density functions.
• We present three applications of our general result: i) In the framework of integrable Quantum Field Theory (IQFT) we present a derivation of the LeClair-Mussardo formula for finite temperature one-point functions.
• We also extend the results to boundary operators in Boundary Field Theories.