- #1
TerryW
Gold Member
- 211
- 17
- Homework Statement
- Use the ADM formalism to derive dynamic and initial value equations
- Relevant Equations
- MTW (21.115) - See attachment
In my earlier post, I demonstrated a way to derive MTW's Equation (21.90),
##16π\mathfrak{L}_{geom} = - \dot π^{ij} γ_{ij} - N\mathcal{H} -N_i\mathcal{H^i}-2(π^{ij}N_j-½N^iTrπ+γ^½N^{|i})_{,i}## MTW (21.90)
I received my first two 'likes' for this which made me really happy - Thanks guys!
I've moved on a bit now and have reached page 525, (four whole pages - wow!) and I am now trying to produce MTW (21.115) - see attachment.
MTW suggests that this can be derived from:
##I = \frac{1}{16π}\int[ \dot π^{ij} γ_{ij} - N\mathcal{H} -N_i\mathcal{H^i}]d^4x + \int\mathfrak{L}_{Field}d^4x ## MTW (21.95)
I've managed to produce nearly all of (21.115) but I cannot find a way to produce the terms I've underlined.
Instead of the term ##(π^{ij}N^m)_{|m}## I have ##(N^iπ^{jk})_{|k}##
I can't see any way to produce terms with ##N^{|ij}## or ##N^{|m}{}_{|m}## from any of the terms in 21.95, but if I go back to (21.90), I can use the term ##[N^{|i}(\gamma)^{\frac{1}{2}}]_{,i}##, which nearly gets me home, but I end up with
##(\gamma)^{\frac{1}{2}}N^{|ij} - \frac{1}{2}(\gamma)^{\frac{1}{2}}g^{ij}N^{|m}{}_{|m}##
and a bonus term## -(-g)^{\frac{1}{2}}\frac{1}{N^2}N^{|i}N_{|i}##
(I have a copy of the original ADM paper and interestingly, they do use the full (21.90) to derive (21.115), ie without dropping the divergence!)
Is there something I have missed that would enable me to show that the bonus term somehow resolves my problems, or is there another route altogether?
Regards
Terry W
Attachment:
##16π\mathfrak{L}_{geom} = - \dot π^{ij} γ_{ij} - N\mathcal{H} -N_i\mathcal{H^i}-2(π^{ij}N_j-½N^iTrπ+γ^½N^{|i})_{,i}## MTW (21.90)
I received my first two 'likes' for this which made me really happy - Thanks guys!
I've moved on a bit now and have reached page 525, (four whole pages - wow!) and I am now trying to produce MTW (21.115) - see attachment.
MTW suggests that this can be derived from:
##I = \frac{1}{16π}\int[ \dot π^{ij} γ_{ij} - N\mathcal{H} -N_i\mathcal{H^i}]d^4x + \int\mathfrak{L}_{Field}d^4x ## MTW (21.95)
I've managed to produce nearly all of (21.115) but I cannot find a way to produce the terms I've underlined.
Instead of the term ##(π^{ij}N^m)_{|m}## I have ##(N^iπ^{jk})_{|k}##
I can't see any way to produce terms with ##N^{|ij}## or ##N^{|m}{}_{|m}## from any of the terms in 21.95, but if I go back to (21.90), I can use the term ##[N^{|i}(\gamma)^{\frac{1}{2}}]_{,i}##, which nearly gets me home, but I end up with
##(\gamma)^{\frac{1}{2}}N^{|ij} - \frac{1}{2}(\gamma)^{\frac{1}{2}}g^{ij}N^{|m}{}_{|m}##
and a bonus term## -(-g)^{\frac{1}{2}}\frac{1}{N^2}N^{|i}N_{|i}##
(I have a copy of the original ADM paper and interestingly, they do use the full (21.90) to derive (21.115), ie without dropping the divergence!)
Is there something I have missed that would enable me to show that the bonus term somehow resolves my problems, or is there another route altogether?
Regards
Terry W
Attachment: