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String Theory
All Roads Lead to String Theory (Polchinski)
Prior to the First Superstring Revolution
Early History S-Matrix Theory
Regge Trajectory
Bosonic String Theory Worldsheet
String
Bosonic String Theory
String Perturbation Theory
Tachyon Condensation
Supersymmetric Revolution Supersymmetry
RNS Formalism
GS Formalism
BPS
Superstring Revolutions
First Superstring Revolution GSO Projection
Type II String Theory
Type IIB String Theory
Type IIA String Theory
Type I String Theory
Type H String Theory
Type HO String Theory
Type HE String Theory
Second Superstring Revolution T-Duality
D-Brane
S-Duality
Horava-Witten String Theory
M-Theory
Holographic Principle
N=4 Super-Yang-Mills Theory
BFSS Matrix Theory
Matrix String Theory
(2,0) Theory
Twistor String Theory
F-Theory
String Field Theory
Pure Spinor Formalism
After the Revolutions
Phenomenology String Theory Landscape
Minimal Supersymmetric Standard Model
String Phenomenology

The AdS/CFT correspondence is an implementation of the Holographic Principle relating String Theory in Anti-de Sitter Space to a Conformal Field Theory on the conformal boundary of that space. [1]

## IntuitionEdit this section

Consider the Holographic Principle. The principle tells us that all information stored within a region is encoded on it's boundary. See Holographic Principle for the intuition behind this principle. Now, this applies to any region, including an Anti-de Sitter Space. The Anti-de Sitter Space has a conformal boundary, on which a Conformal Field Theory,or CFT, is defined. Therefore, a Quantum Gravitational Theory in Anti-de Sitter Space, or AdS (space) for short, is equivalent to a Conformal Field Theory on it's Conformal Boundary..

## ExamplesEdit this section

### Maldacena's Original ExampleEdit this section

Maldacena's paper discusses three examples of AdS/CFT duality. First and best-known is the duality between Type IIB String Theory on $AdS_5 \times S^5$, and N=4 Super-Yang-Mills Theory. Also considered were M-Theory on $AdS_4 \times S^7$, which is dual to ABJM Theory (but the equations for ABJM Theory were not figured out until 2008), and M-Theory on $AdS_7 \times S^4$, which is dual to (2,0) Theory.

Consider a stack of $N$ D3 Branes. They form Yang-Mills Supermultiplets with 4-Dimensional $\mathcal{N} = 4$ Supersymmetry. The vector hypermultiplets are transforming under a gauge group $U(N)\cong SU(N)\times U(1)$. In the infrared, the graviational dynamics and strings decouple, and the $U(1)$ hypermultiplet decouples, while the $SU(N)$ hypermultiplets remain interacting as the beta function is zero. Notice that we know have a Conformal Field Theory with $\mathcal{N}=4$ Supersymmetry. Note that this metric background is that of an extremal 3-Brane black hole. The distance to the event horizon is logarithmically divergent, so it is infinitely far away. As one approaches the event horizon, the geometry approaches $AdS_5 \times S^5$. This is the original motivation for AdS/CFT [1].

### AdS5/CFT4 exampleEdit this section

The Stress-Energy Operator on the Conformal Field Theory is dual to the transverse components of the metric on the Anti-de Sitter.

## The Conformal BoundaryEdit this section

Parameterise the Anti-de Sitter Space as follows:

$ds^2 = (kz)^{-2}\left( dz^2 + \eta_{\mu\nu} \, dx^\mu \, dx^\nu \right)$

Apply a Conformal Transformation , we get

$\mathrm{d}s^2 = \mathrm{d}z^2 + \eta_{\mu\nu}\mathrm{d}x^\mu \mathrm{d}x^\nu$

Which becomes the Minkowski Metric when $z=0$, which is the boundary. This is called the Conformal Boundary.

## Mathematical FormulationEdit this section

We deform the Conformal Field Theory by adding the Source Fields

$\int \mbox{d}x^D j_{CFT}(x)\mathcal{O}(x)$

This is now dual to a theory on Anti-de Sitter Space with a bulk field $j$. This space would have the boundary condition

$\lim\limits_{\mathrm{boundary} } j \omega^{\Delta-d+n} = J_{\text{CFT}}$

Here, $\Delta$ is the Conformal Dimension of the Gauge-Invariant Operator $\mathcal{O}$ and $n$ is the number of covariant indices of $\mathcal{O}$ minus the number of contravariant indices.

$\left\langle \mathcal{T}\left\{ \exp\left(\int \mathrm{d}x^D J_{4D}(x)\mathcal{O}(x)\right) \right\} \right\rangle_{\mathrm{CFT}} = Z_{\mathrm{AdS}}\left[\lim_{\mathrm{boundary}} J \omega^{\Delta-D+n } = J_{4D}\right]$

The LHS is the Vacuum Expectation Value of the time-ordered exponential of the operators over the Conformal Field Theory. The right hand side is the generating functional for the Quantum Gravity with the given Conformal Boundary Condition. The RHS is evaluated by finding the classical solutions to the effective action subject to the given boundary conditions.

## Black Hole FirewallsEdit this section

AdS CFT strongly suggests that the formation and evaporation of a black hole are unitary. It has however been argued [2], [3] , [4], that this does not allow for a smooth event horizon to a black hole. The argument for this goes that the CFT lacks certain operators that describe the interior.

However, in [5] [6], such operators were constructed by Suvrat Raju and Kyriakos Papadodimias.

## Related dualitiesEdit this section

### AdS/CMTEdit this section

AdS/CMT is an application of AdS/CFT to apply String Theory to Condensed Matter Physics. See [7] .

### AdS/QCDEdit this section

AdS/QCD is a generalisation of AdS/CFT in which the "CFT" is not a real CFT, but instead Quantum Chromodynamics, which is not a Conformal Field Theory, but still a Quantum Field Theory. See [8] and [9]

### Kerr/CFTEdit this section

 This section is empty. You can help by adding to it.

### Fluid/GravityEdit this section

 This section is empty. You can help by adding to it.

## ReferencesEdit this section

1. 1.0 1.1 Juan M. Maldacena (1998). "The Large N limit of superconformal field theories and supergravity". Advances in Theoretical and Mathematical Physics 2: 231–252. arXiv:hep-th/9711200. Bibcode 1998AdTMP...2..231M.
2. Almheri, Ahmed; Marlof, Donald., Polchinski, Joseph., Sully, James. (2013). "Black Holes: Complementarity or Firewalls?" (PDF). ArXiV. Retrieved 2014-02-16.
3. Almheri, Ahmed; Marlof, Donald., Polchinski, Joseph., Sully, James., Stanford, Douglas. (2013). "An apologia for firewalls". Journal of High Energy Physics (Springer). Retrieved 2014-02-16.
4. Marlof, Donald; Polchinski,Joseph. (2013). "Gauge/Gravity Duality and the Black Hole Interior" (PDF). Physics Review Letters. Retrieved 2014-02-16.
5. Raju, Suvrat; Papadodimias, Kyriakos. (2013). "The Black Hole Interior in AdS/CFT and the Information Paradox" (PDF). Physics Review Letters. Retrieved 2014-02-16.
6. Raju, Suvrat; Papadodimias, Kyriakos. (2013). [http://arxiv.org/pdf/1310.6335v2.pdf "State-Dependent Bulk-Boundary Maps and Black Hole Complementarity"] (PDF). ArXiV. Retrieved 2014-02-16.
7. Sachdev, Subir; Chesler, P., Lucas, A. (2013). "Conformal Field theories in a periodic potential: results from holography and Field theory". Physics Review C..
8. 't Hooft, Gerard. "A planar diagram theory for strong interactions". Nuclear Physics B (Elsevier).
9. Erlich, Joshua. "Recent Results in AdS/QCD". PoS Confinement.