Noncommutative Bispectral Algebras and their Presentations

TL;DR

This paper establishes minimal presentations for certain noncommutative algebras related to the matrix bispectral problem, connecting them to integrable systems and confirming a conjecture by Grünbaum.

Contribution

It provides new minimal presentations for noncommutative bispectral algebras and links them to spin Calogero-Moser systems, advancing understanding of their structure.

Findings

Finitely presented bispectral algebras for scalar and matrix eigenvalues.

Positive resolution of Grünbaum's conjecture on these algebras.

Connection established between bispectral algebras and integrable systems.

Abstract

We prove a general result on presentations of finitely-generated algebras and apply it to obtain nice presentations for some noncommutative algebras arising in the matrix bispectral problem. By "nice presentation" we mean a presentation that has as few as possible defining relations. This in turn, has potential applications in computer algebra implementations and examples. Our results can be divided into three parts. In the first two, we consider bispectral algebras with the eigenvalue in the physical equation to be scalar-valued for $2\times 2$ and $3\times 3$ matrix-valued eigenfunctions. In the third part, we assume the eigenvalue in the physical equation to be matrix-valued and draw an important connection with spin Calogero-Moser systems. In all cases, we show that these algebras are finitely presented. As a byproduct, we answer positively a conjecture of F.~A.~Gr\"{u}nbaum about these algebras.