Lie Derivative of one-form: an identity

In summary, the conversation discusses an identity for the Lie derivative of a smooth one-form, which states that for smooth vector fields X and Y, and a smooth one-form alpha, the Lie derivative of the bracket [X, Y] is equal to the bracket of the Lie derivatives of X and Y acting on alpha. The student is struggling with expanding the Lie derivatives and is seeking help with understanding the Leibniz rule.
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Homework Statement


I am trying to prove an identity for the Lie derivative of a smooth one-form. The identity is: for X, Y smooth vector fields, alpha a smooth one-form, we have:
$$L_{[X, Y]}\alpha = [L_X, L_Y]\alpha$$ For anyone familiar with the book, this is exercise 5.26 in the first edition of Nakahara: Geometry, Topology, and Physics.

Homework Equations


I am given the identity: for X, Y smooth vector fields, alpha a smooth one-form,
$$(L_X\alpha)(Y)=L_X(\alpha(Y))-\alpha([X, Y])$$ ([X, Y] is the Lie Bracket of the vector fields X and Y, and $$L_XY=[X, Y])$$

The Attempt at a Solution


I keep trying to expand the lie derivatives and cancel terms but I think I am missing a property of the lie derivative; maybe I'm messing up the Leibniz rule or something? Any help would be greatly appreciated!
 
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  • #2
A:By definition, $L_{[X,Y]}\alpha=d(i_{[X,Y]}\alpha)+i_{[X,Y]}d\alpha$. $L_X\alpha = d(i_X\alpha)+i_Xd\alpha$ and $L_Y\alpha = d(i_Y\alpha)+i_Yd\alpha$.From the leibniz rule:$$(L_X\circ L_Y-L_Y\circ L_X)\alpha = d(i_Xd(i_Y\alpha)-i_Yd(i_X\alpha))+i_Xd(i_Yd\alpha)-i_Yd(i_Xd\alpha))$$Now, using the identity you have been given,$$L_{[X,Y]}\alpha=d(i_{[X,Y]}\alpha)+i_{[X,Y]}d\alpha=d(i_Xd(i_Y\alpha)-i_Yd(i_X\alpha))+i_Xd(i_Yd\alpha)-i_Yd(i_Xd\alpha))=$$$$(L_X\circ L_Y-L_Y\circ L_X)\alpha$$
 

Related to Lie Derivative of one-form: an identity

1. What is the Lie Derivative of a one-form?

The Lie Derivative of a one-form is a mathematical operation used in differential geometry to describe how a one-form changes along a given vector field. It is denoted by the symbol ℓXω and is defined as the directional derivative of the one-form ω along the vector field X.

2. How is the Lie Derivative of a one-form calculated?

The Lie Derivative of a one-form is calculated using the formula ℓXω = X(ω) - ω(LXX), where X(ω) is the directional derivative of the one-form ω along the vector field X, and LXX is the Lie bracket of X with itself.

3. What is the significance of the Lie Derivative of a one-form?

The Lie Derivative of a one-form is important in differential geometry and general relativity, as it allows us to describe how a one-form changes along a given vector field. This is useful in understanding the behavior of physical quantities, such as energy and momentum, in curved spacetime.

4. Can the Lie Derivative of a one-form be extended to higher dimensions?

Yes, the Lie Derivative can be extended to higher dimensions, including tensors of any rank. This is known as the Lie Derivative of tensors and follows similar principles as the Lie Derivative of a one-form.

5. How is the Lie Derivative of a one-form related to Lie groups?

The Lie Derivative of a one-form is closely related to Lie groups, which are mathematical structures that describe continuous symmetries. In fact, the Lie bracket used in the calculation of the Lie Derivative is derived from the commutator operation in Lie groups. This connection allows for the application of Lie theory to problems in differential geometry and physics.

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