Resolving disagreement for eta/s in a CFT plasma at finite coupling

The ratio of shear viscosity to entropy density in a strongly coupled CFT plasma can be computed using the AdS/CFT correspondence either from equilibrium correlation functions or from the Janik-Peschanski dual of the boost invariant plasma expansion. We point out that the previously found disagreement for eta/s at finite t' Hooft coupling is resolved once the incoming-wave boundary condition for metric fluctuations at the horizon of the dual geometry is properly imposed.Comment: 7 page

Quantum phase transitions in cascading gauge theory

We study a ground state of N=1 supersymmetric SU(K+P) x SU(K) cascading gauge theory of Klebanov et.al [1,2] on R x S^3 at zero temperature. A radius of S^3 sets a compactification scale mu. An interplay between mu and the strong coupling scale Lambda of the theory leads to an interesting pattern of quantum phases of the system. For mu > mu_cSB=1.240467(8)Lambda the ground state of the theory is chirally symmetric. At mu=mu_cSB the theory undergoes the first-order transition to a phase with spontaneous breaking of the chiral symmetry. We further demonstrate that the chirally symmetric ground state of cascading gauge theory becomes perturbatively unstable at scales below mu_c=0.950634(5)mu_cSB. Finally, we point out that for mu < 1.486402(5)Lambda the stress-energy tensor of cascading gauge theory can source inflation of a closed Universe.Comment: 62 pages, 9 figure

Critical phenomena in N=4 SYM plasma

Strongly coupled N=4 supersymmetric Yang-Mills plasma at finite temperature and chemical potential for an R-symmetry charge undergoes a second order phase transition. We demonstrate that this phase transition is of the mean field theory type. We explicitly show that the model is in the dynamical universality class of 'model B' according to the classification of Hohenberg and Halperine, with dynamical critical exponent z=4. We study bulk viscosity in the mass deformed version of this theory in the vicinity of the phase transition. We point out that all available models of bulk viscosity at continuous phase transition are in conflict with our explicit holographic computations.Comment: 52 pages, 10 figure

Inflation in warped geometries

We argue that brane anti-brane inflation in string theory de-Sitter vacua of Kachru-Kallosh-Linde-Trivedi (KKLT) is captured by the dynamics of a D3-brane probe in the local KKLT model constructed in hep-th/0203041. This provides a framework to study in a controllable way corrections to the inflationary slow roll parameter \eta due to conformal symmetry breaking in a warped geometry throat. We compute the leading correction to \eta for the inflation in the Klebanov-Tseytlin throat geometry. We find that in certain regime this correction tends to decrease \eta. Computations in a different regime suggest however that it is unlikely that \eta << 1 can be achieved with the D3-brane throat inflation.Comment: 17 pages, Late

Bulk viscosity of gauge theory plasma at strong coupling

We propose a lower bound on bulk viscosity of strongly coupled gauge theory plasmas. Using explicit example of the N=2^* gauge theory plasma we show that the bulk viscosity remains finite at a critical point with a divergent specific heat. We present an estimate for the bulk viscosity of QGP plasma at RHIC.Comment: 5 pages, 4 figure

The shear viscosity of gauge theory plasma with chemical potentials

We consider strongly coupled gauge theory plasma with conserved global charges that allow for a dual gravitational description. We study the shear viscosity of the gauge theory plasma in the presence of chemical potentials for these charges. Using gauge theory/string theory correspondence we prove that at large 't Hooft coupling the ratio of the shear viscosity to the entropy density is universal.Comment: 13 pages, no figure

Can the correlated stability conjecture be saved?

Correlated stability conjecture (CSC) proposed by Gubser and Mitra [1,2] linked the thermodynamic and classical (in)stabilities of black branes. In [3] it was shown that the thermodynamic instabilities, specifically the negative specific heat, indeed result in the instabilities in the hydrodynamic spectrum of holographically dual plasma excitations. Counter-examples of CSC were presented in the context of black branes with scalar hair undergoing a second-order phase transition [4,5]. The latter translationary invariant horizons have scalar hair, raising the question whether the asymptotic parameters of the scalar hair can be appropriately interpreted as additional charges leading to a generalization of the thermodynamic stability criterion. In this paper we show that the generalization of the thermodynamic stability criterion of this type can not save CSC. We further present a simple statistical model which makes it clear that thermodynamic and dynamical (in)stabilities generically are not correlated.Comment: 9 pages, 2 figures; v2: JHEP versio

Thermodynamics of the N=2^* strongly coupled plasma

Gauge/string duality is a potentially important framework for addressing the properties of the strongly coupled quark gluon plasma produced at RHIC. However, constructing an actual string theory dual to QCD has so far proven elusive. In this paper, we take a partial step towards exploring the QCD plasma by investigating the thermodynamics of a non-conformal system, namely the N=2^* theory, which is obtained as a mass deformation of the conformal N=4 gauge theory. We find that at temperatures of order the mass scale, the thermodynamics of the mass deformed plasma is surprisingly close to that of the conformal gauge theory plasma. This suggests that many properties of the quark gluon plasma at RHIC may in fact be well described by even relatively simple models such as that of the conformal N=4 plasma.Comment: 41 pages, 22 figure

Hydrodynamics of Sakai-Sugimoto model in the quenched approximation

We study transport properties of the finite temperature Sakai-Sugimoto model. The model represents a holographic dual to 4+1 dimensional supersymmetric SU(N_c) gauge theory compactified on a circle with anti-periodic boundary conditions for fermions, coupled to N_f left-handed quarks and N_f right-handed quarks localized at different points on the compact circle. We analytically compute the speed of sound and the sound wave attenuation in the quenched approximation. Since confinement/deconfinement (and the chiral symmetry restoration) phase transitions are first order in this model, we do not see any signature of these phase transitions in the transport properties.Comment: 15 pages, late