Andrei Starinets

Abstract:

We find quasinormal modes of near extremal black branes by solving a singular boundary value problem for the Heun equation. The corresponding eigenvalues determine the dispersion law for the collective excitations in the dual strongly coupled (Formula presented) supersymmetric Yang-Mills theory at finite temperature. © 2002 The American Physical Society.

Abstract:

We study the absorption of a minimally coupled scalar in the gravitational background created by a stack of near-extremal black three-branes, and more generally by M2-, M5- and Dp-branes. The absorption probability has the form P(l)=P0(l)fl(λ), where P0(l) is the partial wave's absorption probability in the extremal case, and the thermal factor fl(λ) depends on the ratio of the frequency of the incoming wave and the Hawking temperature, λ=ω/πT. Using Langer-Olver's method, we obtain a low-temperature (λ≫1) asymptotic expansion for P(l) with coefficients determined recursively. This expansion, which turns out to be a fairly good approximation even for λ~1, accounts for all power-like finite-temperature corrections to P0(l), and we calculate a few terms explicitly. We also show that at low temperature the absorption probability contains exponentially suppressed terms, and attempt to develop an approximation scheme to calculate those. The high-temperature expansion is also considered. For the s-wave, the low-temperature gravity result is consistent with the free finite-temperature field theory calculation, while for high temperature and higher partial waves we find a disagreement. As a check of the approximation methods used, we apply them to the D1-D5-brane system, and compare results to the known exact solution. © 2001 Elsevier Science B.V.

Abstract:

Conformal field theory was employed to compute the shear viscosity of strongly coupled supersymmetric Yang-Mills plasma. Relation of viscosity to the absorption cross-section of low-energy gravitons falling on a black brane was studied. The shear viscosity was found to be constant for a finite Hooft coupling limit.

Abstract:

Using the anti-de Sitter/conformal field theory correspondence, we relate the shear viscosity eta of the finite-temperature N = 4 supersymmetric Yang-Mills theory in the large N, strong-coupling regime with the absorption cross section of low-energy gravitons by a near-extremal black three-brane. We show that in the limit of zero frequency this cross section coincides with the area of the horizon. From this result we find eta = pi / 8N(2)T3. We conjecture that for finite 't Hooft coupling g(2)(YM)N the shear viscosity is eta = f(g(2)(YM)N)N2T3, where f(x) is a monotonic function that decreases from O(x(-2)ln(-1)(1/x)) at small x to pi/8 when x-->infinity.