Hi, I've recently read an introductory review of Bethe ansatz for antiferromagnetic spin-1/2 Heisenberg chains : cond-mat: 9809163. I understand that the elementary excitations above the ground state in absence of magnetic field are spinons. The article claims that when a finite magnetic field is applied the excitations can be described as psinons, which are 1/2 spin particles (like spinons) and they also represented as holes among the Bethe-quantum numbers (like spinons). However I couldn't really tell what is the exact difference between these two particles. Can somebody explain this?