- Curvature form
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In differential geometry, the curvature form describes curvature of a connection on a principal bundle. It can be considered as an alternative to or generalization of curvature tensor in Riemannian geometry.
Contents
Definition
Let G be a Lie group with Lie algebra
, and P → B be a principal G-bundle. Let ω be an Ehresmann connection on P (which is a
-valued one-form on P).
Then the curvature form is the
-valued 2-form on P defined by
Here d stands for exterior derivative,
is defined by
and D denotes the exterior covariant derivative. In other terms,
Curvature form in a vector bundle
If E → B is a vector bundle. then one can also think of ω as a matrix of 1-forms and the above formula becomes the structure equation:
where
is the wedge product. More precisely, if
and
denote components of ω and Ω correspondingly, (so each
is a usual 1-form and each
is a usual 2-form) then
For example, for the tangent bundle of a Riemannian manifold, the structure group is O(n) and Ω is a 2-form with values in o(n), the antisymmetric matrices. In this case the form Ω is an alternative description of the curvature tensor, i.e.
using the standard notation for the Riemannian curvature tensor,
Bianchi identities
If θ is the canonical vector-valued 1-form on the frame bundle, the torsion Θ of the connection form ω is the vector-valued 2-form defined by the structure equation
where as above D denotes the exterior covariant derivative.
The first Bianchi identity takes the form
The second Bianchi identity takes the form
and is valid more generally for any connection in a principal bundle.
References
- S.Kobayashi and K.Nomizu, "Foundations of Differential Geometry", Chapters 2 and 3, Vol.I, Wiley-Interscience.
See also
- Connection (principal bundle)
- Basic introduction to the mathematics of curved spacetime
- Chern-Simons form
- Curvature of Riemannian manifolds
- Gauge theory
Various notions of curvature defined in differential geometry Differential geometry of curves Differential geometry of surfaces Riemannian geometry Curvature of connections Categories:- Differential geometry
- Curvature (mathematics)
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