On the thermodynamic limit of form factor expansions of dynamical correlation functions in the massless regime of the XXZ spin $1/2$ chain

Understand

This work constructs a well-defined and operational form factor expansion in a model having a massless spectrum of excitations.

• More precisely, the dynamic two-point functions in the massless regime of the XXZ spin-1/2 chain are expressed in terms of properly regularised series of multiple integrals.
• These series are obtained by taking, in an appropriate way, the thermodynamic limit of the finite volume form factor expansions.
• The series are structured in way allowing one to identify directly the contributions to the correlator stemming from the conformal-type excitations on the Fermi surface and those issuing from the massive excitations (deep holes, particles and bound states).