Approximating the coefficients of the Bessel functions
Andrew Yao
TL;DR
The paper analyzes the asymptotics of Bessel functions $J_a^{\mathcal{R}(\theta)}(x)$ tied to root systems $A^{N-1}$, $B^N$, $C^N$, and $D^N$ by studying Dunkl operators and their bilinear form. It establishes equivalence between the growth of coefficients in logarithmic inputs and the asymptotics of the Dunkl bilinear form under large-$N$ scaling in several regimes, and derives leading-order terms for the corresponding bilinear forms across types A, BC, and D. A graded-ring framework of operators is developed to connect these asymptotics with eigenfunctions, enabling detailed expansions for Bessel coefficients and enabling weak-convergence results to free or rectangular free convolutions. The results generalize prior limits-probability frameworks and provide combinatorial and gamma-function expressions that describe the dominant contributions, with implications for universality and representation-theoretic structure of Dunkl-type harmonic analysis on root systems.
Abstract
For the type A, BC, and D root systems, we determine equivalent conditions between the coefficients of an exponential holomorphic function and the asymptotic values taken by the Dunkl bilinear form when one of its entries is the function. We establish these conditions over the $|θN| \rightarrow\infty$ regime for the type A and D root systems and over the $|θ_0 N|\rightarrow \infty, \frac{θ_1}{θ_0 N}\rightarrow c\in\mathbb{C}$ regime for the type BC root system. We also generalize existing equivalent conditions over the $θN \rightarrow c\in\mathbb{C}$ regime for the type A root system and over the $θ_0 N\rightarrow c_0\in\mathbb{C}, \frac{θ_1}{θ_0 N}\rightarrow c_1\in\mathbb{C}$ regime for the type BC root system and prove new equivalent conditions over the $θN \rightarrow c\in\mathbb{C}$ regime for the type D root system. Furthermore, we determine the asymptotics of the coefficients of the Bessel functions over the regimes that we have mentioned.
