A Canonical Positive Definite Kernel Associated with the $ξ$-Bergman Kernel

Abstract

Let $Ω\subset \mathbb{C}^{n}$ and $ξ\in \ell^{1}$. The $ξ$-Bergman kernel $K_{ξ, Ω}$, introduced by Bao and Guan, generalizes the classical Bergman kernel by replacing the point evaluation functional with a functional determined by sequence $ξ$. While this kernel inherits several important extremal and plurisubharmonic properties, it is intrinsically an on-diagonal object and therefore lacks the two-variable reproducing kernel structure that lies at the heart of the classical Bergman theory. The purpose of this paper is to associate a canonical Hermitian positive-definite kernel with the $ξ$-Bergman kernel and to investigate its analytic and geometric properties. Our construction is based on the family of Riesz representatives corresponding to the $ξ$-evaluation functionals. More precisely, we introduce a Hermitian kernel obtained as the Gram kernel of these representatives and show that it is positive definite and for $z \in Ω$ satisfies \[ B_{ξ,Ω}(z,z)=K_{ξ,Ω}(z), \] thereby recovering the $ξ$-Bergman kernel as its diagonal restriction. As a consequence, we prove that the $ξ$-Bergman kernel is real analytic on $Ω$. We also establish biholomorphic transformation laws, and obtain a representation of the $ξ$-Bergman kernel in terms of derivatives of the classical Bergman kernel. Furthermore, we obtain explicit formulas for the $ξ$-Bergman kernel on the upper half-plane $\mathbb{H}$ corresponding to several classes of sequences $ξ$, establish corresponding $ξ$-Lu Qi-Keng results, and derive precise boundary asymptotics. These examples illustrate how the choice of the differential functional influences both the zero set and the boundary growth of the associated kernel.