Abundance of Bergman metrics with constant positive holomorphic sectional curvature

TL;DR

This paper constructs uncountably many Reinhardt domains in complex dimensions two and higher with Bergman metrics locally isometric to multiples of the Fubini--Study metric, answering a longstanding open question.

Contribution

It provides the first known examples of such manifolds for all positive integers m and n ≥ 2, demonstrating the complexity of classifying these geometries.

Findings

Constructed uncountably many Reinhardt domains with specified Bergman metrics.

Proved these domains are mutually Bergman inequivalent.

Resolved the open case for dimensions n ≥ 2 in the classification of such manifolds.

Abstract

An outstanding open question, which has attracted renewed attention following the pioneering work of Huang--Li--Treuer, is whether, for a given positive integer $m$, there exists a complex manifold whose Bergman metric is locally isometric to $m$ times the Fubini--Study metric. Previously, this question had only been resolved in the case $m=1$. In this paper, we construct, for any pair of positive integers $(m,n)$ with $n \geq 2$, an $\mathbb{R}$-parameter (hence uncountable) family of Reinhardt domains in $\mathbb{C}^n$ whose Bergman metrics are all locally isometric to $m$ times the Fubini--Study metric. Moreover, we show that the domains in this family are mutually Bergman inequivalent. This not only answers the folklore question, but also suggests that a reasonable classification of the geometry of such complex manifolds is infeasible. We also note such examples cannot exist in dimension one. The results complete the remaining open case in the study of complex manifolds whose Bergman space separates points and whose Bergman metric has constant holomorphic sectional curvature. Our approach differs from existing methods in the literature. We reduce the construction to a mapping problem and apply a Brouwer fixed point argument to establish the existence of the desired domains.