Formula relating covariant derivative and exterior derivative According to Gallot-Hulin-Lafontaine one has d alpha (X_0,...,X_q) = sum_{i=0}^q (-1)^i D_{X_i} alpha (X_1,...,X_{i-1},X_0,X_{i+1},...,X_q) It seems to me that it should be d alpha (X_0,...,X_q) = sum_{i=0}^q (-1)^i D_{X_i} alpha (X_0,...,hat{X_i},...,X_q)

inhiba5f

inhiba5f

Answered question

2022-09-03

Formula relating covariant derivative and exterior derivative
According to Gallot-Hulin-Lafontaine one has
d α ( X 0 , , X q ) = i = 0 q ( 1 ) i D X i α ( X 1 , , X i 1 , X 0 , X i + 1 , , X q )
It seems to me that it should be
d α ( X 0 , , X q ) = i = 0 q ( 1 ) i D X i α ( X 0 , , X i ^ , , X q )
Is this right ?

Answer & Explanation

Lorenzo Aguilar

Lorenzo Aguilar

Beginner2022-09-04Added 18 answers

If θ is a 1-form, then
d θ ( X , Y ) = ( X θ ) ( Y ) ( Y θ ) ( X )
If Ω is a 2-form, then
d Ω ( X , Y , Z ) = ( X Ω ) ( Y , Z ) + ( Z Ω ) ( X , Y ) + ( Y Ω ) ( Z , X )
and so on ... but you have to have a zero-torsion (symmetric) connection. These formulae will be useful when manipulating structure equations, for instance to obtain Bianchi identities.
obojeneqk

obojeneqk

Beginner2022-09-05Added 3 answers

If the vector fields commute (for example, if the X k 's are the vector fields associated to a coordinate system), then it reduces to your formula.
It's not even clear to me how to interpret the terms for i=0 or i=1 in their formula, and in any case the factor ( 1 ) i looks strange, since they would get the alternating signs from the moving of the argument X 0 anyway.

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