In complex geometry, a part of mathematics, a Calabi–Eckmann manifold (or, often, Calabi–Eckmann space), named after Eugenio Calabi and Beno Eckmann, is a complex, homogeneous, non-Kähler manifold, homeomorphic to a product of two odd-dimensional spheres of dimension ≥ 3. The Calabi–Eckmann manifold is constructed as follows. Consider the space , where , equipped with an action of the group : where is a fixed complex number. It is easy to check that this action is free and proper, and the corresponding orbit space M is homeomorphic to . Since M is a quotient space of a holomorphic action, it is also a complex manifold. It is obviously homogeneous, with a transitive holomorphic action of A Calabi–Eckmann manifold M is non-Kähler, because . It is the simplest example of a non-Kähler manifold which is simply connected (in dimension 2, all simply connected compact complex manifolds are Kähler). The natural projection induces a holomorphic map from the corresponding Calabi–Eckmann manifold M to . The fiber of this map is an elliptic curve T, obtained as a quotient of by the lattice . This makes M into a principal T-bundle. Calabi and Eckmann discovered these manifolds in 1953. Notes Complex manifolds