Multiple orthogonal polynomials and a counterexample to the Gaudin Bethe Ansatz Conjecture

Jacobi polynomials are polynomials whose zeros form the unique solution of the Bethe Ansatz equation associated with two irreducible modules. We study sequences of polynomials whose zeros form the unique solution of the Bethe Ansatz equation associated with two highest weight irreducible modules, with the restriction that the highest weight of one of the modules is a multiple of the first fundamental weight.

We describe the recursion which can be used to compute these polynomials. Moreover, we show that the first polynomial in the sequence coincides with the Jacobi-Piñeiro multiple orthogonal polynomial and others are given by Wronskian-type determinants of Jacobi-Piñeiro polynomials.

As a byproduct we describe a counterexample to the Bethe Ansatz Conjecture for the Gaudin model.