What is Jacobi's identity for Lie derivatives on a smooth manifold?

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In summary, Jacobi's identity for Lie derivatives on a smooth manifold is a mathematical formula that relates the Lie derivative of two vector fields to the Lie derivative of their commutator. It is an important tool in differential geometry and Lie theory, and can be derived using the definition of the Lie derivative and properties of the Lie bracket. It can also be extended to higher-order Lie derivatives and has applications in various areas of mathematics and physics.
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Euge
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Here is this week's POTW:

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Prove that for all vector fields $X$, $Y$, and $Z$ on a smooth manifold, their Lie derivatives $\mathscr{L}_X$, $\mathscr{L}_Y$, and $\mathscr{L}_Z$ satisfies Jacobi’s identity $$[\mathscr{L}_X,[\mathscr{L}_Y,\mathscr{L}_Z]] + [\mathscr{L}_Y, [\mathscr{L}_Z,\mathscr{L}_X]] + [\mathscr{L}_Z, [\mathscr{L}_X, \mathscr{L}_Y]] = 0$$

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No one answered this week's problem. You can read my solution below.
Let $X, Y, Z$ be vector fields on a smooth manifold $M$. They satisfy Jacobi's identity $[[X,Y], Z] + [[Y,Z],X] + [[Z,X],Y] = 0$, so $\mathscr{L}_{[[X,Y],Z]} + \mathscr{L}_{[[Y,Z],X]} + \mathscr{L}_{[[Z,X],Y]}.$ Therefore

$$[[\mathscr{L}_X,\mathscr{L}_Y], \mathscr{L}_Z] + [[\mathscr{L}_Y,\mathscr{L}_Z],\mathscr{L}_X] + [[\mathscr{L}_Z,\mathscr{L}_X], \mathscr{L}_Y]$$
$$=[\mathscr{L}_{[X,Y]},\mathscr{L}_Z] + [\mathscr{L}_{[Y,Z]}, \mathscr{L}_X] + [\mathscr{L}_{[Z,X]},\mathscr{L}_Y]$$
$$=\mathscr{L}_{[[X,Y],Z]} + \mathscr{L}_{[[Y,Z],X]} + \mathscr{L}_{[[Z,X],Y]}$$
$$= 0$$
 

1. What is Jacobi's identity for Lie derivatives on a smooth manifold?

Jacobi's identity for Lie derivatives on a smooth manifold is a mathematical formula that relates the Lie derivative of two vector fields to the Lie derivative of their commutator. It can be written as [X, [Y, Z]] = [[X, Y], Z] + [Y, [X, Z]], where X, Y, and Z are vector fields on the manifold.

2. What is the significance of Jacobi's identity?

Jacobi's identity is an important tool in differential geometry and Lie theory. It helps to understand the behavior of vector fields on a smooth manifold and is used in various applications, such as in the study of Lie algebras and Lie groups.

3. How is Jacobi's identity derived?

Jacobi's identity can be derived using the definition of the Lie derivative and properties of the Lie bracket (commutator). By expanding the expression for the Lie derivative of [X, Y] and rearranging the terms, Jacobi's identity can be obtained.

4. Can Jacobi's identity be extended to higher-order Lie derivatives?

Yes, Jacobi's identity can be extended to higher-order Lie derivatives. For example, the second-order Lie derivative of a vector field can be written as [X, [X, Y]] = [[X, X], Y] + [X, [X, Y]]. This can be generalized to higher-order derivatives by adding more commutators.

5. What are some applications of Jacobi's identity?

Jacobi's identity has applications in various areas of mathematics and physics. It is used in the study of Lie algebras, which have applications in quantum mechanics and group theory. It is also used in the study of differential equations and geometric structures on manifolds, such as in the theory of dynamical systems and in general relativity.

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