Hyperkaehler structures on total spaces of holomorphic cotangent bundles

TL;DR

This paper constructs a canonical hyperkaehler structure on the total space of the cotangent bundle of a Kaehler manifold near the zero section, extending it under real-analytic conditions and establishing a hyperkaehler Darboux-Weinstein theorem.

Contribution

It introduces a canonical hyperkaehler structure on $T^*M$ near the zero section, extending it globally for real-analytic metrics, and proves a hyperkaehler Darboux-Weinstein theorem.

Findings

Existence of a canonical hyperkaehler structure near the zero section

Extension of the hyperkaehler structure under real-analyticity

A hyperkaehler analog of the Darboux-Weinstein theorem

Abstract

Let $M$ be a Kaehler manifold, and consider the total space $T^*M$ of the cotangent bundle to $M$. We show that in the formal neighborhood of the zero section $M \subset T^*M$ the space $T^*M$ admits a canonical hyperkaehler structure, compatible with the complex and holomorphic symplectic structures on $T^*M$. The associated hyperkaehler metric $h$ coincides with the given Kaehler metric on the zero section $M \subset T^*M$. Moreover, $h$ is invariant under the canonical circle action on $T^*M$ by dilatations along the fibers of $T^*M$ over $M$. We show that a hyperkaehler structure with these properties is unique. When the Kaehler metric on $M$ is real-analytic, we show that this formal hyperkaehler structure can be extended to an open neighborhood of the zero section. We also prove a hyperkaehler analog of the Darboux-Weinstein Theorem. To prove these results, we use the machinery of $R$-Hodge structures, following Deligne and Simpson.