Sklyanin-like algebras for ($q$-)linear grids and ($q$-)para-Krawtchouk polynomials

TL;DR

This paper introduces S-Heun operators on linear and q-linear grids, linking them to Sklyanin-like algebras and special polynomials, providing new algebraic interpretations and finite-dimensional representations.

Contribution

It develops a unified framework for S-Heun operators related to Sklyanin-like algebras and introduces finite-dimensional polynomial bases with algebraic significance.

Findings

S-Heun operators act naturally on Continuous Hahn and Big q-Jacobi polynomials.

Finite-dimensional representations yield para-Krawtchouk and q-para-Krawtchouk polynomials.

Heun operators are expressed as quadratic combinations of S-Heun operators.

Abstract

S-Heun operators on linear and $q$-linear grids are introduced. These operators are special cases of Heun operators and are related to Sklyanin-like algebras. The Continuous Hahn and Big $q$-Jacobi polynomials are functions on which these S-Heun operators have natural actions. We show that the S-Heun operators encompass both the bispectral operators and Kalnins and Miller's structure operators. These four structure operators realize special limit cases of the trigonometric degeneration of the original Sklyanin algebra. Finite-dimensional representations of these algebras are obtained from a truncation condition. The corresponding representation bases are finite families of polynomials: the para-Krawtchouk and $q$-para-Krawtchouk ones. A natural algebraic interpretation of these polynomials that had been missing is thus obtained. We also recover the Heun operators attached to the corresponding bispectral problems as quadratic combinations of the S-Heun operators