Intrinsic characterization of projective special complex manifolds

TL;DR

This paper introduces an intrinsic characterization of projective special complex manifolds using c-projective structures, constructs hypercomplex structures on certain bundles, and explores conditions for flatness of quaternionic structures.

Contribution

It generalizes Mantegazza's characterization of projective special Kähler manifolds and links c-projective structures with hypercomplex and quaternionic geometries.

Findings

Characterization of projective special complex manifolds via c-projective structures.

Construction of non-trivial hypercomplex structures on tangent bundles.

Identification of conditions for flat quaternionic structures related to c-projective flatness.

Abstract

We define the notion of an $S^1$-bundle of projective special complex base type and construct a conical special complex manifold from it. Consequently the base space of such an $S^{1}$-bundle can be realized as $\mathbb{C}^{\ast}$-quotient of a conical special complex manifold. As a corollary, we give an intrinsic characterization of a projective special complex manifold generalizing Mantegazza's characterization of a projective special K\"ahler manifold. Our characterization is in the language of c-projective structures. As an application, a non-trivial $S^1$-family of Obata-Ricci-flat hypercomplex structures (given by a generalization of the rigid c-map) on the tangent bundle of the total space of a $\mathbb{C}^*$-bundle over a complex manifold with certain kind of c-projective structure is constructed. Finally, we show that the quaternionic structure underlying any of these hypercomplex structures is in general not flat and that its flatness implies the vanishing of the c-projective Weyl tensor of the base of the $\mathbb{C}^*$-bundle. Conversely, any c-projectively flat complex manifold satisfying a cohomological integrality condition gives rise to a flat quaternionic structure.