Cohomology and Extensions
Formal Lie groupoids
For the orthogonal group is the group of isometries of a real -dimensional Hilbert space. This is naturally a Lie group. This is canonically isomorphic to the group of orthogonal matrices.
More generally there is a notion of orthogonal group of an inner product space.
The analog for complex Hilbert spaces is the unitary group.
The homotopy groups of are for and for sufficiently large (“stable range”) are
In the unstable range for low they instead start out as follows (e.g. Abanov 09, A.18.104.22.168).
Whitehead tower and higher orientation structures
The Whitehead tower of the orthogonal group plays an important role in applications related to quantum physics.
The first steps are
Fivebrane group to String group to Spin group to special orthogonal group to orthogonal group.
Given a manifold , lifts of the structure map of the -principal bundle to which the tangent bundle is associated through this tower define, respectively
fivebrane group string group spin group special orthogonal group orthogonal group
|group||symbol||universal cover||symbol||higher cover||symbol|
|orthogonal group||Pin group||Tring group|
|special orthogonal group||Spin group||String group|
|anti de Sitter group|
|super Poincaré group|
Examples of sporadic (exceptional) isogenies from spin groups onto orthogonal groups are discussed in
The homotopy groups of are listed for instance in
- Alexander Abanov, Homotopy groups of Lie groups 2009 (pdf)
Revised on November 4, 2013 01:38:14
by Urs Schreiber