Luis Hervella

The sixteen classes of almost Hermitian manifolds and their linear invariants

SummaryIt is shown that in a natural way there are precisely sixteen classes of almost Hermitian manifolds.

Curvature of indefinite almost contact manifolds

The curvature tensor of indefinite almost contact manifolds is investigated. By means of the study of the Jacobi operator along spacelike, timelike and null geodesies, spaces of constant curvature are characterized as well as spaces of pointwise constant ϕ-sectional curvature. As an extension of these conditions we introduce the socalled ϕ-isotropic spaces and show a local classification of such manifolds.