Gauss-Bonnet Theorem / Invariant |
In General > s.a. euler class and euler number.
* Idea:
(a.k.a. Gauss-Bonnet-Chern theorem) An important result in differential
geometry relating the geometry of a closed surface to its topology.
* Conditions: It
applies only for Riemannian (positive-definite) metrics.
* Relationships: It
can be considered as a special case of the Atiyah-Singer index theorem.
$ 2D version: If
M is a compact two-dimensional Riemannian manifold with Gaussian
curvature K, and Kg
is the the geodesic curvature of the boundary ∂M
2π χ(M) = ∑i (π − αi) + ∫∂M Kg ds + ∫M K dA ,
where αi are
the internal angles of ∂M (i = 1, ..., n)
(∫ K dA can be a surface integral; In 2D, the Einstein
tensor is identically zero).
$ 4D version: If
Rabcd is the Riemann
curvature tensor of a compact oriented 4D manifold,
χ(M) = ∫M d4v (Rabcd Rabcd − 4 Rab Rab + R2)
(it vanishes for M homeomorphic to \(\mathbb R\)4).
* Even-dimensional, orientable manifold:
If e(F) is the Euler class, ∫M e(F)
= χ(M).
* Complex n-dimensional manifold:
(They are all even-dimensional and orientable) ∫M
cn(F)
= χ(M).
References > s.a. Gauss-Bonnet Gravity.
@ General: Labbi Sigma(07)-a0709-proc [Gauss-Bonnet invariants in arbitrary dimensions and applications];
Szczęsny et al IJGMP(09)-a0810 [new elementary proof];
Li a1111 [overview].
@ Lorentzian:
in Hartle & Sorkin GRG(81).
@ Generalizations: Alty JMP(95) [with boundary and arbitrary signature];
Bao & Chern AM(96) [for Finsler spaces];
Arnlind et al a1001 [for matrix analogues of embedded surfaces];
Zhao JGP(15)-a1408 [for a general connection].
> Online resources:
see MathWorld page;
Wikipedia page.
> In higher dimensions:
see Wikipedia page.
main page
– abbreviations
– journals – comments
– other sites – acknowledgements
send feedback and suggestions to bombelli at olemiss.edu – modified 26 sep 2016