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**Selected Topics in AdS/CFT lecture 1**

Soo-Jong Rey Seoul National University 1st Asian Winter School in String Theory January 2007

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**Topics: Loops, Defects and Plasma**

Review of AdS5/SYM4 Wilson/Polyakov loops Baryons, Defects Time-Dependent Phenomena

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Starting Point string theory:open + closed strings low-energy limit of string theory: open string ! gauge theory (spin=1) closed string ! gravity theory (spin=2) channel duality: open $ closed

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**Channel Duality open string channel time closed string channel**

gauge dynamics gravity dynamics

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**Gauge – Gravity Duality**

keypoint: “gauge theory dynamics” (low energy limit of open string dynamics) is describable by “gravity dynamics” (low-energy limit of closed string dynamics) and vice versa

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**Tool Kits for AdS/CFT elementary excitations:**

open string + closed string solitons: D-branes (quantum) + NS-branes (classical) Mach’s principle: spacetime Ã elementary + soliton sources “holography”: gravity fluctuations = source fluctuations

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**p-Brane (gravity description)**

string effective action S = s d10x [e-2(R(10)+(r )2+|H3|2 + …) +( p |Gp+2|2 + … ) ] = (1/g2st)(NS-NS sector) + (R-R sector) H3 = d B2, Gp+2 = d Cp+1 etc. R-R sector is “quantum” of NS-NS sector

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**elementary and solitons**

fixed “magnetic” charge, energy-minimizing static configurations (necessary condition for BPS states) NS 5-brane: E = s g-2st [(r )2 + H32] > g-2st sS3 e-2 H3 F-string: E = s [g-2st (r )2 + g2st K72] > g0st sS7 K7 Mass: M(string) ~ 1 ; M(NS5) ~ (1/g2st) “elementary” ; “soliton”

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**p-brane: in between p-brane:**

E = s g-2st (r )2 + (Gp+2)2 > g-1st s e- Gp+2 M(p-brane) » (1/gst) p-brane = “quantum soliton”: more solitonic than F-string but less solitonic than NS5-brane F-string $ p-brane $ NS5-brane quantum treatment of p-brane is imperative

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**Dp-brane (CFT description)**

strings can end on it open string string endpoints labelled by Chan-Paton factors ( ) = (i,j) mass set by disk diagram M ~ 1/gst ---- identifiable with p-brane QL = QR (half BPS object)

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**SYMp+1 at Low-Energy infinite tension limit (’ 0)**

open strings rigid rods (Mw ~ r/’) (N,N) string dynamics U(N) SYM(P+1) L = g-2YM Tr ( Fmn “||” + (Dm a)2 + [a, b] “?” + …. )

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**Static source: heavy quarks**

semi-infinite string (M ~ 1) at rest or constant velocity (static source) labelled by a single Chan-Paton factor ( ) = (i) heavy (anti)quark in (anti)fundamental rep.

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**Perturbation theory (1)**

large N conformal gauge theory : double expansion in 1/N and 2 = gYM2 N SYM = (N /2) s d4 x Tr (Fmn2 + (Dm )2 + …) planar expansion: (N /2)V – E NF = (1/N)2h-2 (2)E-V 2 : nonlinear interactions 1/N: quantum fluctuations observable: h l (1/N)2h-2(2)l Cl, h

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**Perturbation theory (2)**

Weak coupling closed string theory: double expansion in gst and ’ ’ : string worldsheet fluctuation Sstring= (½’) s d2 X ¢ X gst : string quantum loop fluctuation SSFT = * QB + gst * * observables = Sh m gst2h – 2 (2’ p2)m Dm, h

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**Identifying the Two Sides….**

large-N YM and closed string theory have the same perturbation expansion structure gst $ (1/N) (’/R2) $ 1/ where R = characteristic scale Maldacena’s AdS/CFT correspondence: “near-horizon”(R) geometry of D3-brane = large-N SYM3+1 at large but fixed not only perturbative level but also nonperturbatively (evidence?)

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**D3-Brane Geometry 10d SUGRA(closed string)+4d SYM (D3-brane):**

Stotal = S10d + sd4 x (-e- TrFmn2+ C4….) Solution ds2 = Z-1/2 dx Z1/2 dy26 G5 = (1+*) dVol4 Æ d Z where Z = (1+R4/r4); r = |y| and R4 = 4 gst N ’2 r ! 1: 10d flat spacetime r ! 0 : characteristic curvature scale = R

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**Identifications At large N, curvedness grows with g2st(N/gst)=gstN**

D-brane stress tensor grows with (N/gst) At large N, curvedness grows with g2st(N/gst)=gstN Near D3-brane, spacetime= AdS5 x S5 4d D3-brane fluct. $ 10d spacetime fluct. (from coupling of D3-brane to 10d fields) Tr (FmpFnp) $ metric gmn Tr (FmnFmn) $ dilaton Tr(FmpF*np) $ Ramond-Ramond C, Cmn

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**AdS/CFT correspondence**

Dirichlet problem in AdS5 or EAdS5=H5 Zgravity = exp (-SAdS5(bulk,a, 1a)) = ZSYM =s[dA] exp(-SSYM - s a 1a Oa) AdS5

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**AdS5 In flat 4+2 dimensional space ds2 = - dX02 – d X52 + a=14 d Xa2**

embed hyperboloid X02 + X52 - a=14 Xa2 = R2 SO(4,2) invariant, homogeneous AdS5 = induced geometry on hyperboloid <homework> derive the following coordinates

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Global coordinates: ds2 = R2(-cosh2 d2+d2+sinh2 d32) boundary = Rt £ S3 Poincare coordinates: ds2=R2[r2(-dt2 + dx2 + dy2 + dz2)+ r-2dr2] boundary = Rt £ R3

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**holographic scaling dimensions**

wave eqn for scalar field of mass m 2 solns: normalizable vs. non-normalizable modes

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**Why AdS Throat = D3-Brane?**

D-brane absorption cross-section: SUGRA computation = SYM computation N D3-branes = flat flat AdS5 AdS_5 “interior” in gravity description = N D3-branes in gauge description

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**Another argument D-instantons probing (Euclidean) AdS5**

For U(N) gauge group, “homogeneous” instanton number < N (otherwise inhomogeneous) Q D-instanton cluster in approx. flat region SDinstanton = -(1/gst ’2) TrQ[1, 2]2 + …. < Tr(1)2 > » QL2, <Tr(2)2 > » Q2 gst ’2 / L2 rotational symmetry implies L4 = Q gst ’2 = N gst ’2

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How can it be that 5d = 4d? extensive quantities in 4d SYM theory scales as [length]4 Extensive quantities in 5d AdS gravity scales as [length]5 So, how can it be that quantities in 4d theory is describable by 5d theory?? [Question] Show both area and volume of a ball of radius X in AdSd scales as Xd-1!

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**Entropy Counting (3+1) SYM on V3 with UV cutoff a**

AdS5 gravity on V3 with UV cutoff a

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Shall we test AdS/CFT? Recall that heavy quarks are represented by fundamental strings attached to D3-brane now strings are stretched and fluctuates inside AdS5 Let’s compute interaction potential between quark and antiquark Do we obtain physically reasonable answers?

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**Static Quark Potential at Zero Temperature**

Notice: Square-Root non-analyticity for exact 1/r conformal invariance

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Notice: R4=gstN’2 ’2 cancels out!

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**Holography (boundary = bulk)**

YM distance scale r= AdS radial scale r=1 Anything that takes place HERE (AdS5) --- --- is a result of that taking place HERE (R3+1)

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**Heavy Meson Configuration**

r= AdS radial scale r=oo YM distance scale bare quark bare anti-quark

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**What have we evaluated? rectangular Wilson loop in N=4 SYM**

W[C] = Tr P exp sC (i Am dxm + a d ya ) gauge field part = Aharonov-Bohm phase scalar field part = W-boson mass unique N=4 supersymmetric structure with contour in 10-dimensions

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**T=0 vs. T>0 SYM Theory T=0 (zero-temperature 4d N=4 SYM):**

ds2 = r2 (-dt2+dx2 ) + dr2/r2 + (dS5)2 r = 5th dim // 4d energy scale: < r < 1 T>0 (finite-temperature 4d N=4 SYM): ds2 = r2 (- F dt2+dx2) + F-1 dr2/r2+(dS5)2 F = (1 - (kT)4/r4): kT < r <1 5d AdS Schwarzschild BH = 4d heat bath

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**Static Quark Potential at Finite Temperature**

Notice: Nonanalyticity in persists exact 1/r persists potential vanishes beyond r*

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**UV-IR relation for T>0**

T=0 relation Maximum inter-quark distance! T>0 relation U*/M

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**Heavy Meson Configuration (T > 0)**

r=M r= AdS radial scale r=oo YM distance scale bare quark bare anti-quark

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**Application: D3-branes on “thermal” S1**

“thermal S1” breaks N=4 susy completely At low-energy, 3d Yang-Mills + (junks) 5d AdS replaced by 5d Euclidean black hole (time $ space) glueball spectrum is obtainable by studying bound-state spectrum of gravity modes Note: 4d space-time, topology: gravity // gauge

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**YM2+1 glueball spectrum 0++: solve dilaton eqn=2nd order linear ode**

result: N=3 lattice N=oo lattice AdS/CFT (41) (55) (input) * (9) (13) ** (17) (22) *** [M. Teper]

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**YM3+1 glueball spectrum Use T>0 D4-brane instead**

0++: solve dilaton eqn=2nd-order linear ODE result: N=3 lattice AdS/CFT (15) (input) * ** *** [M. Teper] other glueballs fit reasonably well (why??)

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**The Story of Square-Root**

branch cut from strong coupling? artifact of N1 limit heuristically, saddle-point of matrices < Tr eM > = s [dM] (Tr eM) exp (--2 Tr M2) Recall modified Bessel function

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