# Orthogonal Polynomials, Asymptotics and Heun Equations

## TL;DR

This paper explores how orthogonal polynomials related to deformed weights satisfy Heun equations in the large degree limit, revealing connections between special functions, asymptotics, and mathematical physics.

## Contribution

It demonstrates that orthogonal polynomials with deformed weights asymptotically satisfy Heun equations, linking classical orthogonal polynomials to these important special functions.

## Key findings

- Orthogonal polynomials satisfy Heun equations as degree n becomes large.
- Connections established between deformed weights and solutions to Heun equations.
- Results applicable to weights supported on various intervals, including (0,1], (a,b).

## Abstract

The Painlev\'{e} equations arise from the study of Hankel determinants generated by moment matrices, whose weights are expressed as the product of ``classical" weights multiplied by suitable ``deformation factors", usually dependent on a ``time variable'' $t$. From ladder operators one finds second order linear ordinary differential equations for associated orthogonal polynomials with coefficients being rational functions. The Painlev\'e and related functions appear as the residues of these rational functions. We will be interested in the situation when $n$, the order of the Hankel matrix and also the degree of the polynomials $P_n(x)$ orthogonal with respect to the deformed weights, gets large. We show that the second order linear differential equations satisfied by $P_n(x)$ are particular cases of Heun equations when $n$ is large. In some sense, monic orthogonal polynomials generated by deformed weights mentioned below are solutions of a variety of Heun equa\-tions. Heun equations are of considerable importance in mathematical physics and in the special cases they degenerate to the hypergeometric and confluent hypergeometric equations. In this paper we look at three type of weights: the Jacobi type, which are are supported $(0,1]$ the Laguerre type and the weights deformed by the indicator function of $(a,b)$ $\chi_{(a,b)}$ and the step function $\theta(x)$.