Generalized TBA and generalized Gibbs

Abstract

We consider the extension of the thermodynamic Bethe Ansatz (TBA) to cases in which additional terms involving higher conserved charges are added to the Hamiltonian, or in which a distinction is made between the Hamiltonian used for time evolution and that used for defining the density matrix. Writing down equations describing the saddle-point (pseudo-equilibrium) state of the infinite system, we prove the existence and uniqueness of solutions for Lieb-Liniger provided simple requirements are met. We show how a knowledge of the saddle-point rapidity distribution is equivalent to that of all generalized chemical potentials, and how the standard equilibrium equations for e.g. excitations are simply generalized.