Excited states in Bethe ansatz solvable models and the dressing of spin and charge

Abstract

A general formalism for the study of excitations above equilibrium in Bethe ansatz solvable models is presented. Nonzero temperature expressions for dressed energy, momentum, spin and charge are obtained. The zero temperature excitations of the Hubbard-Shastry models are examined in detail, and special attention is paid to the dressing of spin and charge of excited quasi-particles. These are in general momentum dependent and are only spin-charge separated when the ground state is half- lled and has zero magnetisation