All Questions
Tagged with gravity general-relativity
322
questions with no upvoted or accepted answers
12
votes
0
answers
1k
views
Variation of the Einstein-Hilbert action in $D$ dimensions without the Gibbons-Hawking-York (GHY) term
Consider the standard Einstein-Hilbert action in $D \ne 2$ dimensions spacetimes :
\begin{equation}
S_{EH} = \frac{1}{2 \kappa} \int_{\Omega} R \; \sqrt{- g} \; d^D x,
\end{equation}
where $\Omega$ is ...
- 7,592
11
votes
0
answers
664
views
What are Galileons good for?
Lately I've seen many papers (for example "The galileon as a local modification of gravity"; 292 total hits on the arXiv) on types of field theories known as Galileons, and I'm wondering ...
- 3,947
8
votes
0
answers
383
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Definition of gravity path integral?
In a non-abelian gauge theory there is a "fundamental" gauge field $A_\mu^a$ with gauge index $a$ often called connection. Although $ A_\mu^a$ is not gauge invariant, gauge invariant quantities can be ...
- 322
8
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215
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Metric transformation, polygons and gravitons
I'm trying to understand the paper by Hitchin called: ''Polygons and gravitons". I'm stuck at page 471.
At this point, he does some computations and obtains a metric:
$$
\gamma dz d\bar{z}+\gamma^{...
- 123
6
votes
1
answer
451
views
Covariant derivative of the vielbein determinant
The vielbein postulate says that
$$\nabla_\mu e_v^{\,a}=\partial_{\mu}e_\nu^{\,a}+\omega_{\mu\,\, b}^{\,\,a}\,e^b_\nu-\Gamma^\sigma_{\mu\nu}\,e^{\,a}_\sigma=0.$$
$\nabla$ is the coordinate covariant ...
- 99
6
votes
0
answers
290
views
What does black hole formation and evaporation actually look like as viewed from far away?
Many people on Physics SE (myself included) have been confused about what black hole formation and evaporation look like when viewed from far away. For example:
Does any particle ever reach any ...
- 48.4k
5
votes
0
answers
82
views
Bargmann–Wigner equations in NP formalism
Bargmann-Wigner equations describe free particles of arbitrary spin $j$, namely
$$(-\gamma^{\mu}\partial_{\mu}+m)_{\alpha_r \alpha_{r’}}\Psi_{\alpha_1,..,\alpha_{r’},...,\alpha_{2j}}=0$$
where we have ...
- 341
5
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0
answers
605
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How to find the Hawking temperature for this metric?
I am reading this paper about "Hawking radiation of Kerr-Newman-de Sitter black hole", where the authors find Hawking temperature of this metric
The authors state that hawking temperature is given by
...
- 265
5
votes
1
answer
319
views
Proportionality Constant in Einstein Field Equations
The Einstein Field Equations: $$G_{ab}~=~8\pi T_{ab}.$$ I am familiar with how to obtain the $8\pi$ proportionality factor through correspondence with Newtonian gravity, but am wondering if this ...
- 960
4
votes
1
answer
169
views
How are objects inside a black hole affected by the gravity of objects outside the black hole?
There are many Q&As about whether something inside a black hole can escape the event horizon if another massive object gets close enough to pull it out. I realize the answer (I think universally ...
- 450
4
votes
3
answers
408
views
Confusion over what constitutes a uniform gravitational field in relativity
Suppose we have some observer moving upwards with a constant proper acceleration, by the equivalence principle this is the same as the observer remaining stationary in a gravitational field, like ...
- 312
4
votes
0
answers
110
views
Effective field theories in curved spacetime
Loosely speaking, in flat spacetime, one defines the effective Lagrangian by writing down all possible operators compatible with the symmetries and suppressed by some energy scale, and one usually ...
- 305
4
votes
0
answers
246
views
Gravity's self-energy
Suppose we have a single massive point particle.
In the absence of "potentials", the content of the stress-energy tensor would be dictated uniquely by the particle's mass and trajectory (...
4
votes
0
answers
23
views
Effect (if any) of strong(ish) gravity radiation on stars
Two black holes merge, and a good few percent of their total mass is converted into gravitational radiation.
Years or decades later, the resulting gravity wave passes through nearby stars. Does it ...
- 700
4
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0
answers
232
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The (Newton-Laplace-Ivory-Arnold) shell theorem in general relativity
It is well-known that Birkhoff's theorem and the classification of LTB spacetimes proves one version of Newton's shell theorem in the context of GR. Another statement in Newtonian gravity, often ...
- 643