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![Page 1: Transport coefficients in strongly coupled gauge theories: insights from string theory Andrei Starinets Perimeter Institute for Theoretical Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649f2f5503460f94c4960e/html5/thumbnails/1.jpg)
Transport coefficients in strongly coupled gauge theories:
insights from string theory
Andrei Starinets
Perimeter Institute for Theoretical Physics
![Page 2: Transport coefficients in strongly coupled gauge theories: insights from string theory Andrei Starinets Perimeter Institute for Theoretical Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649f2f5503460f94c4960e/html5/thumbnails/2.jpg)
Collaboration: Dam SonGiuseppe PolicastroChris HerzogAlvaro NunezPavel KovtunAlex BuchelJim LiuAndrei ParnachevPaolo Benincasa
References:
hep-th/0205051 hep-th/0205052 hep-th/0302026 hep-th/0309213 hep-th/0405231 hep-th/0406124hep-th/0506144 hep-th/0506184 hep-th/0507026
![Page 3: Transport coefficients in strongly coupled gauge theories: insights from string theory Andrei Starinets Perimeter Institute for Theoretical Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649f2f5503460f94c4960e/html5/thumbnails/3.jpg)
The goal is to compute transport coefficients (e.g. shear and bulk viscosity) and the speed of sound in thermal QCD
This is of interest for hydrodynamic models applied to RHIC data (elliptic flow)
Transport coefficients are hard to compute from “first principles”, even in perturbation theory. (For example, no perturbative calculation of bulk viscosity in gauge theory is available.)
Lattice approach cannot be used directly.
![Page 4: Transport coefficients in strongly coupled gauge theories: insights from string theory Andrei Starinets Perimeter Institute for Theoretical Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649f2f5503460f94c4960e/html5/thumbnails/4.jpg)
Transport coefficients and the speed of sound can be computed from string theory for SOME thermal gauge theories in nonperturbative regime
This calculation is based on approach known as “gauge/gravity duality” or “AdS/CFT correspondence”
AdS = Anti de Sitter spaceCFT = Conformal Field Theory
![Page 5: Transport coefficients in strongly coupled gauge theories: insights from string theory Andrei Starinets Perimeter Institute for Theoretical Physics.](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649f2f5503460f94c4960e/html5/thumbnails/5.jpg)
Gauge-gravity duality in string theory
Perturbative string theory: open and closed strings(at low energy, gauge fields and gravity, correspondingly)
Nonperturbative theory: D-branes (“topological defects” in 10d)
Complementary description of D-branes by open (closed) strings:
perturbative gauge theory description OK
perturbative gravity description OK
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Computing transport coefficients from “first principles”
Kubo formulae allow one to calculate transport coefficients from microscopic models
In the regime described by a gravity dual the correlator can be computed using AdS/CFT
Fluctuation-dissipation theory(Callen, Welton, Green, Kubo)
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Shear viscosity in SYM
Correction to : A.Buchel, J.Liu, A.S., hep-th/0406264
P.Arnold, G.Moore, L.Yaffe, 2001
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Universality of
Theorem:
For any thermal gauge theory (with zero chemicalpotential), the ratio of shear viscosity to entropy density is equal to in the regime describedby a corresponding dual gravity theory
Remark:
Gravity dual to QCD (if it exists at all) is currentlyunknown.
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A viscosity bound conjecture
P.Kovtun, D.Son, A.S., hep-th/0309213, hep-th/0405231
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Two-point correlation function of
stress-energy tensor Field theory
Zero temperature:
Finite temperature:
Dual gravity
Five gauge-invariant combinations of and other fields determine
obey a system of coupled ODEs Their (quasinormal) spectrum determines singularities of the correlator
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Bulk viscosity and the speed of sound in SYM
is a “mass-deformed” (Pilch-Warner flow)
Finite-temperature version: A.Buchel, J.Liu, hep-th/0305064
The metric is known explicitly for Speed of sound and bulk viscosity:
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Epilogue
AdS/CFT gives insights into physics of thermal gauge theories in the nonperturbative regime
General algorithm exists to compute transport coefficients and the speed of sound in any gravity dual
Model-independent statements can presumably be checked experimentally
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Hydrodynamics as an effective theory
Thermodynamic equilibrium:
Near-equilibrium:
Eigenmodes of the system of equations
Shear mode (transverse fluctuations of ):
Sound mode:
For CFT we have and
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Relation to RHIC IF quark-gluon plasma is indeed formed in heavy ion collisions
IF a hydrodynamic regime is unambiguously proven to exist
THEN hydrodynamic MODELS describe experimental results for e.g. elliptic flows well, provided
Bulk viscosity and speed of sound results are potentially interesting
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Example: supersymmetric Yang-Millstheory at finite temperature
Fields:
The theory is conformal (coupling doesn’t run)
In the limit the theory is described by a gravity dual (AdS-Schwarzschild black hole)