Symmetry, Integrability and Geometry: Methods and Applications (SIGMA)

SIGMA 22 (2026), 106, 32 pages      arXiv:2510.00843      https://doi.org/10.3842/SIGMA.2026.106

Partition Functions of Two-Dimensional Coulomb Gases with Circular Root- and Jump-Type Singularities

Kohei Noda
Institut de Recherche en Mathématique et Physique, Université Catholique de Louvain, Louvain-la-Neuve, 1348, Belgium

Received January 15, 2026, in final form October 10, 2026; Published online October 30, 2026

Abstract
In this paper, we study the random polynomial $p_n(\rho):=\prod_{j=1}^n (|z_j|-\rho)$, where the points $\{z_j\}_{j=1}^n$ are the eigenvalues of random normal matrices with a radially symmetric potential. We establish precise large $n$ asymptotic expansions for the moment generating function $\mathbb{E}\bigl[{\rm e}^{(u \operatorname{Im}\log p_n(\rho))/\pi} {\rm e}^{a\operatorname{Re}\log p_n(\rho)}\bigr]$, $u\in\mathbb{R}$, $a>-1$, where $\rho>0$ lies in the bulk of the spectral droplet. The asymptotic expansion is expressed in terms of parabolic cylinder functions, which confirms a conjecture of Byun and Charlier. This also provides the first free energy expansion of two-dimensional Coulomb gases with general circular root- and jump-type singularities. While the $a=0$ case has already been widely studied in the literature due to its relation to counting statistics, we also obtain new results for this special case.

Key words: random normal matrices; counting statistics; partition functions; asymptotics.

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