Bergman--Einstein Rigidity for Hartogs Domains over Bounded Homogeneous Domains

Abstract

We prove a rigidity theorem for the Bergman metric on Hartogs domains over bounded homogeneous domains. Let $Ω\subset \mathbb C^n$ be a bounded homogeneous domain, let $K_Ω$ denote its Bergman kernel, and consider $$ Ω_{m,s}:=\{(z,ζ)\in Ω\times \mathbb C^m:\ \|ζ\|^2 -C_Ω. $$ For $s\neq 0$, we prove that the following conditions are equivalent: the Bergman metric of $Ω_{m,s}$ is Kähler--Einstein; $Ω_{m,s}$ is homogeneous; $Ω_{m,s}$ is biholomorphic to $\mathbb B^{n+m}$; and $Ω\cong\mathbb B^n$ with $s=\frac1{n+1}$. This gives a positive answer to Yau's question within this class and may be viewed as a Cheng-type rigidity phenomenon beyond the smoothly bounded strictly pseudoconvex setting. The proof combines the explicit formula for the Bergman kernel of $Ω_{m,s}$ with the structural invariants of the bounded homogeneous base.