$2\times2$ Hypergeometric operators with diagonal eigenvalues (1810.08560v1)

Abstract: In this work we classify all the order-two Hypergeometric operators $D$, symmetric with respect to some $2\times 2$ irreducible matrix-weight $W$ such that $DP_n=P_n\left(\begin{smaLLMatrix} \lambda_n&0\0&\mu_n \end{smaLLMatrix} \right)$ with no repetition among the eigenvalues ${\lambda_n,\mu_n}{n\in\mathbb N_0}$, where ${P_n}{n\in\mathbb N_0}$ is the (unique) sequence of monic orthogonal polynomials with respect to $W$. We obtain, in a very explicit way, a three parameter family of such operators and weights. We also give the corresponding monic orthongonal polynomials, their three term recurrence relation and their squared matrix-norms.