33
votes
Why is Sachdev-Ye-Kitaev (SYK) Model model important?
People hope that it may be an example of AdS/CFT correspondence that can be completely understood.
AdS/CFT correspondence itself has been an incredibly important idea in the hep-th community over the ...
- 1,470
21
votes
Why is Sachdev-Ye-Kitaev (SYK) Model model important?
SYK model provides us with the simplest example of holography which is much easier to study than canonical $AdS_5 \times S^5$ case due to much lower dimensionality. It was the initial motivation for ...
- 1,996
8
votes
Why is there a Cardy formula in 2D CFT?
This question was just bumped to the homepage, so let me try to give a physical answer to explain why modular invariance is particular to two dimensions. The Cardy formula tells you something about ...
- 231
8
votes
Accepted
AdS Space Black Holes Penrose Diagram
The difference lies in spatial infinity: AdS like spacetimes have timelike infinity while Schwarzschild spacetime has a lightlike infinity.
In general the prescription to build Penrose diagrams of ...
- 641
8
votes
Accepted
Isn't AdS/CFT an end to String theory as a fundamental theory?
If string theory were really a UV completion of gravity then it would make a prediction for quantum gravity S-matrix elements when Newton's constant is large. But this cannot be done with the ...
- 8,421
8
votes
Accepted
About the paper "Traversable wormhole dynamics on a quantum processor"
It is just a calculation with 9 (noisy) qubits, easily simulated on a classical computer. There is no reason to do it on real quantum hardware except to demonstrate that the hardware functions as ...
- 28.2k
7
votes
Accepted
D3-brane in AdS/CFT correspondance
$3$-branes are special in the following sense: only for $p=3$, the black p-brane solution admits a constant dilaton, while it is running for $p\not=3$. In particular, the dilaton $\phi$ diverges at ...
- 3,572
7
votes
Differences and relations between CFTs defined on the complex plane and CFTs defined on the torus?
A CFT on any surface must have an associative OPE. This constrains both the spectrum and the OPE coefficients. This condition is enough for the CFT to be consistent on the plane, but not on the torus. ...
- 2,752
7
votes
Is there non-locality in the AdS/CFT?
You may find a small set of articles discussing non-commutative field theories, or dipole field theories, or field theories in the presence of a magnetic field. These types of field theories will ...
- 1,470
7
votes
Accepted
AdS/CFT scalar 3-point function integral from Feynman parametrization?
A few months ago, I also needed the result of this computation of the three-point contact Witten diagram by
Freedman, Mathur, Matusis and Rastelli. I was also flabbergasted by the lack of detail in ...
- 6,167
7
votes
Accepted
Does string theory violate general covariance?
Superstring theory has many local symmetries that are not manifest, coming from the BRST charge identifications in the covariant formalism, $|\psi\rangle\cong|\psi\rangle + Q|\chi\rangle$. Those ...
- 5,804
7
votes
Accepted
Relationship between scaling dimension and mass in AdS/CFT
This is a bit long, but I'm going to be super precise.
Let's work in Poincare coordinates in AdS,
$$
ds^2 = \frac{L^2}{z^2} ( dz^2 + dx^\mu dx_\mu ) .
$$
$\Delta$ is the eigenvalue of scale ...
- 26.9k
6
votes
Is $\mathcal{N} = 4$ SYM a "toy model"?
$\mathcal N = 4$ SYM is useful to study aspects of perturbation theory, especially since exact solutions are known. It is not possible to describe our physical world with it though.
You mention the ...
- 9,169
6
votes
Accepted
de-Sitter space as near-horizon limit of Black Holes
For 4D spacetimes with positive cosmological constant, de Sitter factor can emerge
as a near-horizon limit in maximal Schwarzschild–de Sitter and Kerr–de Sitter black holes, when the event horizon of ...
- 16k
6
votes
Accepted
String theory in ${\rm AdS}_3$ and the ${\rm SL}{(2,\mathbb{R})}$ WZW model on the worldsheet
Preliminary: $\mathrm{AdS_3}$ can be embedded in $\mathbb R^{2,2}$ subject to the hyperboloid constraint $-\eta_{\mu\nu}x^\mu x^\nu=L^2$, $\eta_{\mu\nu}=\mathrm{diag}(-1,-1,1,1)$. This can ...
- 8,510
6
votes
Accepted
Computing the DBI action on $S^5$
It should work as follows. By your "ansatz" the relevant metric reduces to
$$ds^2 = -(1- \dot{\phi}^2\sin^2 \theta)dt^2 + d\theta^2 + \cos^2 \theta d\Omega_3^2 \ ,$$
where $d\Omega_3^2$ is ...
- 909
6
votes
Accepted
Calculation of interaction of gravitational waves with a black hole
I don't know why you need AdS/CTF correspondence for that? There is a good derivation found here (page 64 to 90). To give a quick overview:
You can calculate the propagation of gravitational waves on ...
- 2,126
5
votes
Has Sen quantized superstring fields?
(Note that I am only starting to study these works and I may be wrong on some points.)
The paper you are quoting is indeed providing a full definition of (type II and heterotic) superstring theory (...
- 850
5
votes
Bulk-to-Boundary propagator
In order to show that some function is the Delta distribution, you have to show that
It is zero except for where the argument of the function vanishes.
It integrates to 1 when integrated over the ...
- 3,572
5
votes
AdS/CFT correspondence and M-theory
1) There is a version of AdS/CFT which relates M-theory on $AdS_7 \times S^4$ background and 6D ${\cal N}=(2,0)$ SCFT which is an effective theory describing the worldvolume physics of M5 branes. See, ...
- 1,996
5
votes
Does CFT in AdS/CFT live in flat spacetime?
The CFT in AdS/CFT lives on the asymptotic boundary of the AdS space. The asymptotic boundary is a conformal manifold associated to any "visibility manifold". See this paper of Eberlein and O'Neil (...
- 8,064
5
votes
Can String Theory really fail to contain a de Sitter vacua?
I haven't read the paper by Danielsson and Van Riet, but they seem to be in good company here.
Recently, four prominent string theorists wrote a paper that suggested (even metastable) De Sitter space ...
- 1,094
5
votes
Why is there no gauge-invariant local operator in GR?
For gauge theories, observables (schematically) are functions of the form
\begin{equation}
\mbox{observable}\colon
\frac{\mbox{phase space}}{\mbox{gauge symmetries}}\to\mathbb{R},
\end{equation}
which ...
- 2,935
5
votes
Accepted
Where is the proof of AdS/CFT?
There are lots of AdS/CFT correspondences, because there are lots of CFTs with the right properties to have a gravity dual. However, as far as I know, none of them have been proven.
Since we don't ...
- 54.7k
5
votes
Accepted
What are the necessary conditions for a CFT to have a holographic dual?
The introduction to this answers a part of my question in a concise manner. The following points are necessary in order for the CFT to have a holographic dual.
The first AdS/CFT papers (Maldacena, ...
- 5,277
5
votes
Accepted
Holographic dual to baryon
A proposal for the holographic dual of QCD is given by the so-called Witten-Sakai-Sugimoto model $[1,2,3]$.
The Witten background is a solution of a consistent truncation of Type IIA supergravity (...
- 6,856
5
votes
Accepted
What does tilde denote here?
If you scroll down to the appendix, that paper uses the notation from this review paper, which in turn defines $\widetilde{\mathrm G}$ to be the universal cover of $\mathrm G$.
- 70.5k
5
votes
Accepted
AdS/CFT with circle boundary
What you're seeing is that if we limit ourselves to the simplest definition of "boundary", then AdS doesn't have one. Taking $z \to 0$ in Poincare co-ordinates
\begin{equation}
ds^2 = \frac{...
- 8,421
5
votes
Accepted
Why and how we study different limits in quantum gravity?
Not a complete answer, but usually these limits are taken to make mathematical calculations possible. For instance when non-perturbative calculations are hard (basically every time) one can expand ...
- 5,023
4
votes
AdS/CFT, QCD & String Phenomenology
Within string theory, the following two quests are not competing and only distantly related:
Finding a UV completion of the Standard Model that incorporates gravity.
Find holographic duals to gauge ...
- 3,572
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