The silence of the little strings
Journal of High Energy Physics (2005) 731-755
Abstract:
We study the hydrodynamics of the high-energy phase of Little String Theory. The poles of the retarded two-point function of the stress energy tensor contain information about the speed of sound and the kinetic coefficients, such as shear and bulk viscosity. We compute this two-point function in the dual string theory and analytically continue it to lorentzian signature. We perform an independent check of our results by the lorentzian supergravity calculation in the background of non-extremal NS5-branes. The speed of sound vanishes at the Hagedorn temperature. The ratio of shear viscosity to entropy density is equal to the universal value 1/4π and does not receive α′ corrections. The ratio of bulk viscosity to entropy density equals 1/10π. We also compute the R-charge diffusion constant. In addition to the hydrodynamic singularities, the correlators have an infinite series of finite-gap poles, and a massless pole with zero attenuation. © SISSA 2005.Coupling constant dependence of the shear viscosity in N = 4 supersymmetric Yang-Mills theory
Nuclear Physics B 707:1-2 (2005) 56-68
Abstract:
Gauge theory-gravity duality predicts that the shear viscosity of N = 4 supersymmetric SU(Nc) Yang-Mills plasma at temperature T in the limit of large N c and large 't Hooft coupling gYM2Nc is independent of the coupling and equals to πNc2T3 /8. In this paper, we compute the leading correction to the shear viscosity in inverse powers of 't Hooft coupling using the α′-corrected low-energy effective action of type IIB string theory. We also find the correction to the ratio of shear viscosity to the volume entropy density (equal to 1/4π in the limit of infinite coupling). The correction to 1/4π scales as (gYM2Nc) -3/2 with a positive coefficient. © 2004 Elsevier B.V. All rights reserved.Holography and hydrodynamics: Diffusion on stretched horizons
Journal of High Energy Physics 7:10 (2003) 1675-1701
Abstract:
We show that long-time, long-distance fluctuations of plane-symmetric horizons exhibit universal hydrodynamic behavior. By considering classical fluctuations around black-brane backgrounds, we find both diffusive and shear modes. The diffusion constant and the shear viscosity are given by simple formulas, in terms of metric components. For a given metric, the answers can be interpreted as corresponding kinetic coefficients in the holographically dual theory. For the near-extremal DP, M2 and M5 branes, the computed kinetic coefficients coincide with the results of independent AdS/CFT calculations. In all the examples, the ratio of shear viscosity to entropy density is equal to ℏ/(4πkB, suggesting a special meaning of this value. © SISSA/ISAS 2003.AdS/CFT correspondence, quasinormal modes, and thermal correlators in N = 4 supersymmetric Yang-Mills theory
Physical Review D - Particles, Fields, Gravitation and Cosmology 67:12 (2003) 1240131-12401312
Abstract:
We use the Lorentzian AdS/CFT prescription to find the poles of the retarded thermal Green's functions of N = 4 SU(N) supersymmetric Yang-Mills theory in the limit of large N and large 't Hooft coupling. In the process, we propose a natural definition for quasinormal modes in an asymptotically AdS spacetime, with boundary conditions dictated by the AdS/CFT correspondence. The corresponding frequencies determine the dispersion laws for the quasiparticle excitations in the dual finite-temperature gauge theory. Correlation functions of operators dual to massive scalar, vector and gravitational perturbations in a five-dimensional AdS-Schwarzschild background are considered. We find asymptotic formulas for quasinormal frequencies in the massive scalar and tensor cases, and an exact expression for vector perturbations. In the long-distance, low-frequency limit we recover results of the hydrodynamic approximation to thermal Yang-Mills theory.AdS/CFT correspondence, quasinormal modes, and thermal correlators in N=4 supersymmetric Yang-Mills theory
Physical Review D 67:12 (2003)