Hyperkaehler structures on total spaces of holomorphic cotangent bundles

Abstract

Let $M$ be a Kaehler manifold, and consider the total space $T^{\ast }M$ of the cotangent bundle to $M$. We show that in the formal neighborhood of the zero section $M\subset T^{\ast }M$ the space $T^{\ast }M$ admits a canonical hyperkaehler structure, compatible with the complex and holomorphic symplectic structures on $T^{\ast }M$. The associated hyperkaehler metric $h$ coincides with the given Kaehler metric on the zero section $M\subset T^{\ast }M$. Moreover, $h$ is invariant under the canonical circle action on $T^{\ast }M$ by dilatations along the fibers of $T^{\ast }M$ 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.

100 pages, LaTeX2e