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Regular \(XXZ\) Bethe states at roots of unity as highest weight vectors of the \(\mathrm{sl}_{2}\) loop algebra. (English) Zbl 1115.82006

Summary: We show that every regular Bethe ansatz eigenvector of the \(XXZ\) spin chain at roots of unity is a highest weight vector of the \(\text{sl}_{2}\) loop algebra, for some restricted sectors with respect to eigenvalues of the total spin operator \(S^{Z}\), and evaluate explicitly the highest weight in terms of the Bethe roots. We also discuss whether a given regular Bethe state in the sectors generates an irreducible representation or not. In fact, we present such a regular Bethe state in the inhomogeneous case that generates a reducible Weyl module. Here, we call a solution of the Bethe ansatz equations which is given by a set of distinct and finite rapidities regular Bethe roots. We call a nonzero Bethe ansatz eigenvector with regular Bethe roots a regular Bethe state.

MSC:

82B20 Lattice systems (Ising, dimer, Potts, etc.) and systems on graphs arising in equilibrium statistical mechanics
82B23 Exactly solvable models; Bethe ansatz