Spin structures on almost-flat manifolds

Almost Flat Manifolds

1.1. We denote by V a connected ^-dimensional complete Riemannian manifold, by d = d(V) the diameter of V, and by c = c(V) and c~ = c~(V), respectively, the upper and lower bounds of the sectional curvature of V. We set c = c(V) = max (| c1, | c~ |). We say that F i s ε-flat, ε > 0, if cd < ε. 1.2. Examples. a. Every compact flat manifold is ε-flat for any ε > 0. b. Every compact nil-manifold p...

Stably and Almost Complex Structures on Bounded Flag Manifolds

We study the enumeration problem of stably complex structures on bounded flag manifolds arising from omniorientations, and determine those induced by almost complex structures. We also enumerate the stably complex structures on these manifolds which bound, therefore representing zero in the complex cobordism ring Ω∗ .

TT - tensors and conformally flat structures on 3 - manifolds

We study transverse-tracefree (TT)-tensors on conformally flat 3-manifolds (M, g). The Cotton-York tensor linearized at g maps every symmetric tracefree tensor into one which is TT. The question as to whether this is the general solution to the TT-condition is viewed as a cohomological problem within an elliptic complex first found by Gasqui and Goldschmidt and reviewed in the present paper. Th...

Geometric Hamiltonian Structures on Flat Semisimple Homogeneous Manifolds

In this paper we describe Poisson structures defined on the space of Serret-Frenet equations of curves in a flat homogeneous space G/H where G is semisimple. These structures are defined via Poisson reduction from Poisson brackets on Lg∗, the space of Loops in g∗. We also give conditions on invariant geometric evolution of curves in G/H which guarantee that the evolution induced on the differen...

Weak Spin(9)-structures on 16-dimensional Riemannian Manifolds