Differential, Difference and Asymptotic Relations for Pollaczek-Jacobi Type Orthogonal Polynomials and Their Hankel Determinants

Abstract

In this paper, we study the orthogonal polynomials with respect to a singularly perturbed Pollaczek-Jacobi type weight $$ w(x,t):=(1-x^2)^α\mathrm{e}^{-\frac{t}{1-x^{2}}},\qquad x\in[-1,1],\;\;α>0,\;\;t>0. $$ By using the ladder operator approach, we establish the second-order difference equations satisfied by the recurrence coefficient $β_n(t)$ and the sub-leading coefficient $\mathrm{p}(n,t)$ of the monic orthogonal polynomials, respectively. We show that the logarithmic derivative of $β_n(t)$ can be expressed in terms of a particular Painlevé V transcendent. The large $n$ asymptotic expansions of $β_n(t)$ and $\mathrm{p}(n,t)$ are obtained by using Dyson's Coulomb fluid method together with the related difference equations. Furthermore, we study the associated Hankel determinant $D_n(t)$ and show that a quantity $σ_n(t)$, allied to the logarithmic derivative of $D_n(t)$, can be expressed in terms of the $σ$-function of a particular Painlevé V. The second-order differential and difference equations for $σ_n(t)$ are also obtained. In the end, we derive the large $n$ asymptotics of $σ_n(t)$ and $D_n(t)$ from their relations with $β_n(t)$ and $\mathrm{p}(n,t)$.