Yang-Mills Plasma Research Articles

Hall conductivity of flavor fields from AdS/CFT correspondence

We use the AdS/CFT correspondence to compute a conductivity associated with massive $\mathcal{N}=2$ supersymmetric hypermultiplet fields at finite baryon density, propagating through an $\mathcal{N}=4$ supersymmetric $SU({N}_{c})$ Yang-Mills plasma in the large ${N}_{c}$, large 't Hooft coupling limit. We do so by introducing external electric and magnetic fields coupled to baryon number and computing the resulting induced current, from which we extract the conductivity tensor. At large hypermultiplet mass we compute the drag force on the charge carriers. We also compute the product of the drag coefficient with the kinetic mass, and find that the answer is unchanged from the zero-density case. The gravitational dual is a probe D7-brane, with a nontrivial world volume gauge field configuration, in an AdS-Schwarzschild background. We identify an effective horizon on the D7-brane world volume analogous to the world sheet horizon observed for strings moving in the same background. We generalize our results to a class of theories described by probe D-branes in various backgrounds.

Spinning dragging strings

We use the AdS/CFT correspondence to compute the drag force experienced by a heavy quark moving through a = 4 SU(N) super Yang-Mills plasma at nonzero temperature and R-charge chemical potential and at large 't Hooft coupling. We resolve a discrepancy in the literature between two earlier studies of such quarks. In addition, we consider small fluctuations of the spinning strings dual to these probe quarks and find no evidence of instabilities. We make some comments about suitable D7-brane boundary conditions for the dual strings.

Wake of a Quark Moving through a Strongly CoupledN=4Supersymmetric Yang-Mills Plasma

The energy density wake produced by a heavy quark moving through a strongly coupled N=4 supersymmetric Yang-Mills plasma is computed using gauge-string duality.

Debye screening in strongly coupled Script N = 4 supersymmetric Yang-Mills plasma

Using the AdS/CFT correspondence, we examine the behavior of correlators of Polyakov loops and other operators in = 4 supersymmetric Yang-Mills theory at non-zero temperature. The implications for Debye screening in this strongly coupled non-Abelian plasma, and comparisons with available results for thermal QCD, are discussed.

Transverse momentum broadening of a fast quark in a Script N = 4 Yang-Mills plasma

We compute the momentum broadening of a heavy fundamental charge propagating through a $\mathcal{N}=4$ Yang Mills plasma at large t' Hooft coupling. We do this by expressing the medium modification of the probe's density matrix in terms of a Wilson loop averaged over the plasma. We then use the AdS/CFT correspondence to evaluate this loop, by identifying the dual semi-classical string solution. The calculation introduces the type ``1'' and type ``2'' fields of the thermal field theory and associates the corresponding sources with the two boundaries of the AdS space containing a black hole. The transverse fluctuations of the endpoints of the string determine $\kappa_T = \sqrt{\gamma \lambda} T^3 \pi$ -- the mean squared momentum transfer per unit time. ($\gamma$ is the Lorentz gamma factor of the quark.) The result reproduces previous results for the diffusion coefficient of a heavy quark. We compare our results with previous AdS/CFT calculations of $\hat{q}$.

Photon and dilepton production in supersymmetric Yang-Mills plasma

By weakly gauging one of the U(1) subgroups of the R-symmetry group, = 4 super-Yang-Mills theory can be coupled to electromagnetism, thus allowing a computation of photon production and related phenomena in a QCD-like non-Abelian plasma at both weak and strong coupling. We compute photon and dilepton emission rates from finite temperature = 4 supersymmetric Yang-Mills plasma both perturbatively at weak coupling to leading order, and non-perturbatively at strong coupling using the AdS/CFT duality conjecture. Comparison of the photo-emission spectra for = 4 plasma at weak coupling, = 4 plasma at strong coupling, and QCD at weak coupling reveals several systematic trends which we discuss. We also evaluate the electric conductivity of = 4 plasma in the strong coupling limit, and to leading-log order at weak coupling. Current-current spectral functions in the strongly coupled theory exhibit hydrodynamic peaks at small frequency, but otherwise show no structure which could be interpreted as well-defined thermal resonances in the high-temperature phase.

Heavy flavor diffusion in weakly coupled Script N = 4 Super Yang-Mills theory

We use perturbation theory to compute the diffusion coefficient of a heavy quark or scalar moving in N=4 SU(N_c) Super Yang-Mills plasma to leading order in the coupling and the ratio T/M<<1. The result is compared both to recent strong coupling calculations in the same theory and to the corresponding weak coupling result in QCD. Finally, we present a compact and simple formulation of the Lagrangian of our theory, N=4 SYM coupled to a massive fundamental N=2 hypermultiplet, which is well-suited for weak coupling expansions.

Energy loss of a heavy quark moving through Script N = 4 supersymmetric Yang-Mills plasma

We use the AdS/CFT correspondence to determine the rate of energy loss of a heavy quark moving through N=4 SU(N_c) supersymmetric Yang-Mills plasma at large 't Hooft coupling. Using the dual description of the quark as a classical string ending on a D7-brane, we use a complementary combination of analytic and numerical techniques to determine the friction coefficient as a function of quark mass. Provided strongly coupled N=4 Yang-Mills plasma is a good model for hot, strongly coupled QCD, our results may be relevant for charm and bottom physics at RHIC.

Hydrodynamics of R-charged black holes

We consider hydrodynamics of N=4 supersymmetric SU(N_c) Yang-Mills plasma at a nonzero density of R-charge. In the regime of large N_c and large 't Hooft coupling the gravity dual description involves an asymptotically Anti- de Sitter five-dimensional charged black hole solution of Behrnd, Cvetic and Sabra. We compute the shear viscosity as a function of chemical potentials conjugated to the three U(1) \subset SO(6)_R charges. The ratio of the shear viscosity to entropy density is independent of the chemical potentials and is equal to 1/4\pi. For a single charge black hole we also compute the thermal conductivity, and investigate the critical behavior of the transport coefficients near the boundary of thermodynamic stability.

Sound waves in strongly coupled non-conformal gauge theory plasma

Using gauge theory/gravity duality we study sound wave propagation in strongly coupled non-conformal gauge theory plasma. We compute the speed of sound and the bulk viscosity of N = 2 ∗ supersymmetric SU ( N c ) Yang–Mills plasma at a temperature much larger than the mass scale of the theory in the limit of large N c and large 't Hooft coupling. The speed of sound is computed both from the equation of state and the hydrodynamic pole in the stress–energy tensor two-point correlation function. Both computations lead to the same result. Bulk viscosity is determined by computing the attenuation constant of the sound wave mode.

Coupling constant dependence of the shear viscosity in [formula omitted] supersymmetric Yang–Mills theory

Gauge theory–gravity duality predicts that the shear viscosity of N = 4 supersymmetric SU ( N c ) Yang–Mills plasma at temperature T in the limit of large N c and large 't Hooft coupling g YM 2 N c is independent of the coupling and equals to π N c 2 T 3 / 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 / 4 π in the limit of infinite coupling). The correction to 1 / 4 π scales as ( g YM 2 N c ) − 3 / 2 with a positive coefficient.

Relativistic particle simulation of color diffusion in a SU(2) Yang–Mills plasma

We report on a relativistic particle-in-cell simulation study of color transport in a SU(2) Yang–Mills plasma. Simulation results reveal that the color distribution starting from a spiky form spreads to a flat one, through a diffusive process in color space. By numerically performing a “Perrin” like experiment, we explicitly show that the ensemble averaged color fluctuation square (〈(ΔI)2〉) grows linearly with time indicating that the color vector of a parton executes Brownian motion in color space. Depending on the choice of input parameters, color diffusion time scale can either be shorter or longer than the momentum diffusion time scale. Simulation results for a case where color diffuses faster than momentum are presented.

Isotropic cosmological singularities: other matter models

Isotropic cosmological singularities are singularities which can be removed by rescaling the metric. In some cases already studied, the existence and uniqueness of cosmological models with data at the singularity has been established (Anguige K and Tod K P 1999 Ann. Phys., NY 276 257–93, 294–320, Anguige K 2000 Ann. Phys., NY 285 395–419). These were cosmologies with, as source, either perfect fluids with linear equations of state or massless, collisionless particles. In this paper, we consider how to extend these results to a variety of other matter models. These are scalar fields, massive collisionless matter, the Yang–Mills plasma given by Choquet-Bruhat (Choquet-Bruhat Y 1996 Yang–Mills plasmas Global Structure and Evolution in General Relativity (Springer Lecture Notes in Physics vol 460) ed S Cotsakis and G W Gibbons (Berlin: Springer)) and matter satisfying the Einstein–Boltzmann equation.

Shear viscosity of strongly coupled N = 4 supersymmetric Yang-Mills plasma.

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.

Transverse modes and chaos in classical SU(2) Yang–Mills plasma

A nonperturbative treatment of the dynamics of purely transverse modes in a classical SU(2) Yang–Mills plasma is carried out. It is found that the equations governing the evolution of transverse modes are similar to the equations for longitudinal modes obtained by Bhatt et al. [4]. We have solved the equations approximately using multiple time scale method. It is observed that in the parameter regime where multiple time scale analysis is valid (when the non-abelian coupling terms are small), a new non-abelian mode appears modulating the frequency of the usual abelian mode. As the non-abelian coupling strength is increased, both frequency and amplitude modulation of the abelian mode is seen. For very large values of non-abelian coupling, chaotic behaviour sets in.

Dynamical chaos in SU(2)⊗U(1) theory

We study the dynamics of the classical homogeneous SU(2)⊗U(1) gauge theory in the spontaneously broken phase. A transition from regular to chaotic dynamics is shown to occur for energy densities ε>0.3 m W 2/ G F≈2×10 10 GeV/fm 3. The regular regime is characterized by a sharp frequency spectrum for the Yang-Mills fields. The frequency spectrum in the chaotic regime is continuous and the sharp frequency lines of the regular regime are dispersed. In the early universe or at high energy densities in a Yang-Mills plasma this transition may have observable effects that can be studied by analyzing the frequency spectrum and the time correlation functions. In the chaotic regime these time correlation functions decay considerably faster than in the regular regime.

The analogy between spin glasses and Yang–Mills fluids

A dictionary of correspondence is established between the dynamical variables for spin-glass fluid and Yang-Mills plasma. The Lie-algebraic interpretation of these variables is presented for the two theories. The noncanonical Poisson bracket for the Hamiltonian dynamics of an ideal spin glass is shown to be identical to that for the dynamics of a Yang–Mills fluid plasma, although the Hamiltonians differ for the two theories. This Poisson bracket is associated to the dual space of an infinite-dimensional Lie algebra of semidirect-product type.