The ADM mass is an asymptotic invariant obtained from the energy and momentum fluxes of an asymptotically flat initial data set. In
spatial dimension , let
be the area of the unit
sphere and
a large Euclidean coordinate sphere. One normalization is
|
(1)
|
|
(2)
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where repeated coordinate indices are summed. If , the Lorentz-invariant mass is
|
(3)
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The name ADM mass also occurs for the energy , so the convention matters when
. The invariant-mass formulation is used in the spacetime
Penrose inequality.