Differential geometry MOC

Lie derivative

Let π‘£π‘Ž βˆˆπ”›(𝑀) be a vector field generating the flow πœ‘. The Lie derivative

L𝑣:Tπ‘π‘ž(𝑀)β†’Tπ‘π‘ž(𝑀)

is an ℝ-linear map defined by1 diff

Lπ‘£π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘ž=lim𝑑→0((πœ‘π‘‘)βˆ—π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘žβˆ’π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘žπ‘‘)=dd𝑑(πœ‘π‘‘)βˆ—π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘žβˆ£π‘‘=0.

It is also possible to define the Lie derivative along a vector π‘£π‘Ž βˆˆπ‘‡π‘π‘€ at a single point.

Algebraic properties

  1. Agreement with other derivatives: L𝑣𝑓 =𝑣(𝑓) =dπ‘“π‘Žπ‘£π‘Ž =βˆ‡π‘£π‘“.
  2. Leibniz rule: L𝑣(𝑆 βŠ—π‘‡) =(L𝑣𝑆) βŠ—π‘‡ +𝑆 βŠ—(L𝑣𝑇).
  3. Commutes with contraction: L𝑣(π‘‡π‘Ž1β‹―π‘β‹―π‘Žπ‘π‘1β‹―π‘β‹―π‘π‘ž) =L𝑣(π‘‡π‘Ž1β‹―π‘β‹―π‘Žπ‘π‘1β‹―π‘β‹―π‘π‘ž).

Relation to the covariant derivative

For any affine connexion βˆ‡, we have

Lπ‘£π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘ž=π‘£π‘βˆ‡π‘π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘žβˆ’π‘βˆ‘π‘–=1π‘‡π‘Ž1β‹―π‘π‘–β‹―π‘Žπ‘π‘1β‹―π‘π‘žβˆ‡π‘π‘–π‘£π‘Žπ‘–+π‘žβˆ‘π‘–=1π‘‡π‘Ž1β‹―π‘Žπ‘π‘1β‹―π‘π‘–β‹―π‘π‘žβˆ‡π‘π‘–π‘£π‘π‘–


develop | en | SemBr

Footnotes

  1. 2009. General relativity, pp. 439–441, C.2 ↩