The Bethe ansatz for the six-vertex and XXZ models: an exposition

Tuesday, 29 November, 2016

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In this paper, we review a few known facts on the coordinate Bethe ansatz. We present a detailed construction of the Bethe ansatz vector \psi and energy \Lambda, which satisfy V \psi = \Lambda \psi, where V is the the transfer matrix of the six-vertex model on a finite square lattice with periodic boundary conditions for weights a=b=1 and c>0. We also show that the same vector \psi satisfies H \psi = E \psi, where H is the Hamiltonian of the XXZ model (which is the model for which the Bethe ansatz was first developed), with a value E computed explicitly.
Variants of this approach have become central techniques for the study of exactly solvable statistical mechanics models in both the physics and mathematics communities. Our aim in this paper is to provide a pedagogically-minded exposition of this construction, aimed at a mathematical audience. It also provides the opportunity to introduce the notation and framework which will be used in a subsequent paper by the authors that amounts to proving that the random cluster model on \mathbb{Z}^2 with cluster weight q>4 exhibits a first-order phase transition.


Hugo Duminil-Copin
Maxime Gagnebin
Matan Harel
Ioan Manolescu
Vincent Tassion