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In general relativity , the Komar superpotential ,[1] corresponding to the invariance of the Hilbert-Einstein Lagrangian
L
G
=
1
2
κ
R
−
g
d
4
x
{\displaystyle {\mathcal {L}}_{\mathrm {G} }={1 \over 2\kappa }R{\sqrt {-g}}\,\mathrm {d} ^{4}x}
, is the tensor density :
U
α
β
(
L
G
,
ξ
)
=
−
g
κ
∇
[
β
ξ
α
]
=
−
g
2
κ
(
g
β
σ
∇
σ
ξ
α
−
g
α
σ
∇
σ
ξ
β
)
,
{\displaystyle U^{\alpha \beta }({{\mathcal {L}}_{\mathrm {G} }},\xi )={{\sqrt {-g}} \over {\kappa }}\nabla ^{[\beta }\xi ^{\alpha ]}={{\sqrt {-g}} \over {2\kappa }}(g^{\beta \sigma }\nabla _{\sigma }\xi ^{\alpha }-g^{\alpha \sigma }\nabla _{\sigma }\xi ^{\beta })\,,}
associated with a vector field
ξ
=
ξ
ρ
∂
ρ
{\displaystyle \xi =\xi ^{\rho }\partial _{\rho }}
, and where
∇
σ
{\displaystyle \nabla _{\sigma }}
denotes covariant derivative with respect to the Levi-Civita connection .
The Komar two-form :
U
(
L
G
,
ξ
)
=
1
2
U
α
β
(
L
G
,
ξ
)
d
x
α
β
=
1
2
κ
∇
[
β
ξ
α
]
−
g
d
x
α
β
,
{\displaystyle {\mathcal {U}}({{\mathcal {L}}_{\mathrm {G} }},\xi )={1 \over 2}U^{\alpha \beta }({{\mathcal {L}}_{\mathrm {G} }},\xi )\mathrm {d} x_{\alpha \beta }={1 \over {2\kappa }}\nabla ^{[\beta }\xi ^{\alpha ]}{\sqrt {-g}}\,\mathrm {d} x_{\alpha \beta }\,,}
where
d
x
α
β
=
ι
∂
α
d
x
β
=
ι
∂
α
ι
∂
β
d
4
x
{\displaystyle \mathrm {d} x_{\alpha \beta }=\iota _{\partial {\alpha }}\mathrm {d} x_{\beta }=\iota _{\partial {\alpha }}\iota _{\partial {\beta }}\mathrm {d} ^{4}x}
denotes interior product , generalizes to an arbitrary vector field
ξ
{\displaystyle \xi }
the so-called above Komar superpotential, which was originally derived for timelike Killing vector fields .
See also
Notes
References