Bethe Equations on the Wrong Side of Equator


Abstract in English

We analyse the famous Baxters $T-Q$ equations for $XXX$ ($XXZ$) spin chain and show that apart from its usual polynomial (trigonometric) solution, which provides the solution of Bethe-Ansatz equations, there exists also the second solution which should corresponds to Bethe-Ansatz beyond $N/2$. This second solution of Baxters equation plays essential role and together with the first one gives rise to all fusion relations.

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