ADM Mass for a diagonal metric

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Discussion Overview

The discussion revolves around the calculation of the ADM mass for a specific diagonal metric in a 4+1 dimensional context. Participants explore the implications of the metric's form, its classification as a black hole, and the generalization of ADM mass definitions from 4 dimensions to 4+1 dimensions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a diagonal metric and seeks assistance in finding the ADM mass, asking for formulas or methods to follow.
  • Another participant questions whether the metric is a general form or specifically a black hole, and raises concerns about the applicability of Birkhoff's theorem in 4+1 dimensions, as well as the need for explicit functions A, B, and C.
  • A later reply confirms that the metric is indeed a black hole and provides explicit forms for the functions A, B, and C, along with the definitions of constants Q and M.
  • One participant references Wald's work, noting that while there are formulas for ADM mass, they are presented in terms of asymptotically Euclidean coordinates and do not provide motivations for their derivation.

Areas of Agreement / Disagreement

Participants express uncertainty about the generalization of ADM mass to 4+1 dimensions and whether the definitions from 4 dimensions apply. There is no consensus on the applicability of Birkhoff's theorem in this context.

Contextual Notes

The discussion highlights limitations regarding the assumptions about the metric's properties and the dependence on specific definitions of ADM mass in higher dimensions. The exact motivations behind the formulas referenced from Wald remain unresolved.

praharmitra
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Given a metric of the form

[tex] ds^2 = A(r) dt^2 + B(r) dr^2 + C(r)^2 (d\theta^2+sin^2\theta d\phi^2 + sin^2\theta sin^2\phi d\psi^2)[/tex]

I want to find the ADM mass of this black hole. Can anyone help me with the formula, or method to follow?
 
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Is it a general metric of that form, or is it a black hole? Are we in 4+1 dimensions? Is it a vacuum solution? I don't know if Birkhoff's theorem applies in 4+1. Are you given the functions A, B, and C explicitly? I don't know if the definition of ADM mass generalizes trivially to 4+1 -- probably it does.
 
bcrowell said:
Is it a general metric of that form, or is it a black hole? Are we in 4+1 dimensions? Is it a vacuum solution? I don't know if Birkhoff's theorem applies in 4+1. Are you given the functions A, B, and C explicitly? I don't know if the definition of ADM mass generalizes trivially to 4+1 -- probably it does.

The metric is a black hole. The exact form of the functions A,B,C are

[tex] A(r) = -h(r)^{-2/3} f(r) \\<br /> B(r) = h(r)^{1/3} f(r)^{-1} \\<br /> C(r) = h(r)^{1/3} r^2 \\[/tex]
where
[tex] h(r) = 1 + Q/r^2 \\<br /> f(r) = 1 + r^2 + Q - M/r^2[/tex]
for two constants Q and M.

We are working in 4+1 dimensional Asymptotically AdS Space.

Could you atleast give me the definition of ADM mass in 4 dimensions, I will try and figure out the generalisation.
 
There are some formulas in Wald, on pg 293, though he doesn't derive them, referring readers to the literature.

Unforutunately, they're presented in terms of asymptotically euclidean coordinates in an asymptotically flat space-time, so you'd have to read Wald's section in chapters 10 and 11 to make any sense of the formulas there - which still don't give any of the motivations, really.
 

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