Publications (12)56.43 Total impact
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ABSTRACT: In a recent paper we have analyzed the AdS/CFT duals to shock waves propagating in the N = 4 \mathcal{N} = 4 plasma. Here we study further properties of the system. In the gravity description we consider the properties of the dual black holes, showing in particular that they are stationary black holes with expanding horizons. This is possible because the horizon is not compact; in the fluid, this corresponds to the situation when entropy is being produced and carried away to infinity. We also consider shocks in dimensionalities d other than four and find that, for plasmas whose duals are given by asymptotically AdS spaces, the exponential tail of the shock on the supersonic side shrinks as g  \frac2d {\gamma^{  \frac{2}{d}}} as the velocity approaches the speed of light (the Lorentz factor γ goes to infinity). This generalizes the behavior g  \frac12 {\gamma^{  \frac{1}{2}}} we have found previously for d = 4. Finally, we consider corrugations of the shock front and show that the shock is stable under such perturbations. There are, however, long lived modes, excitations of which describe generation of sound by the shock wave, the energy for this being provided by the incoming fluid. KeywordsGaugegravity correspondence–AdSCFT Correspondence–Holography and quarkgluon plasmas  [Show abstract] [Hide abstract]
ABSTRACT: Shock waves are supersonic disturbances propagating in a fluid and giving rise to dissipation and drag. Weak shocks, i.e., those of small amplitude, can be well described within the hydrodynamic approximation. On the other hand, strong shocks are discontinuous within hydrodynamics and therefore probe the microscopics of the theory. In this paper we consider the case of the strongly coupled N=4 plasma whose microscopic description, applicable for scales smaller than the inverse temperature, is given in terms of gravity in an asymptotically $AdS_5$ space. In the gravity approximation, weak and strong shocks should be described by smooth metrics with no discontinuities. For weak shocks we find the dual metric in a derivative expansion and for strong shocks we use linearized gravity to find the exponential tail that determines the width of the shock. In particular we find that, when the velocity of the fluid relative to the shock approaches the speed of light $v\to 1$ the penetration depth $\ell$ scales as $\ell\sim (1v^2)^{1/4}$. We compare the results with second order hydrodynamics and the IsraelStewart approximation. Although they all agree in the hydrodynamic regime of weak shocks, we show that there is not even qualitative agreement for strong shocks. For the gravity side, the existence of shock waves implies that there are disturbances of constant shape propagating on the horizon of the dual black holes. Comment: 47 pages, 8 figures; v2:typos corrected, references added  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the bulk viscosity, drag force and jet quenching parameter in Improved Holographic QCD. We find that the bulk viscosity rises near the phase transition but does not exceed the shear viscosity. The drag force shows the effects of asymptotic freedom both as a function of velocity and temperature. It indicates diffusion times of heavy quarks in rough agreement with data. The jet quenching parameter values computed via the lightlike Wilson loop are in the lower range suggested by data. Comment: Latex, 61 pages, 18 eps figures. Published version: bulk viscosity section expanded, discussion improved, 2 appendices added; v3: minor mistakes corrected; v4: mistake in eq. (4.21) corrected.  [Show abstract] [Hide abstract]
ABSTRACT: In this note a new method for computing the entanglement entropy of a CFT holographically is explored. It consists of finding a bulk background with a boundary metric that has the conical singularities needed to compute the entanglement entropy in the usual QFT definition. An explicit calculation is presented for d=2.  [Show abstract] [Hide abstract]
ABSTRACT: It has been known for a long time that certain supersymmetric gauge theories can be described by string theory. These gauge theories share common features with QCD when the temperature of the theory is above the confinement temperature. Recently there has been strong evidence, even though not conclusive, that a Quark Gluon Plasma (QGP) above the confinement temperature is formed from gold on gold collisions at the Relativistic Heavy Ion Collider. Furthermore the evidence suggests that the QGP is strongly coupled, making a string description of the plasma possible. We use the dual string theory of the maximally supersymmetric gauge theory to find the profile of the gluonic fields sourced by a moving heavy quark through the plasma, suggesting that a picture of a wake is possible in string theory. Later on, inspired by the qualitative agreement between the measured thermalization time and the predicted time from a dual model we calculate some lowlying gravitational modes in an asymptotically AdS black hole. We find good agreement with the modes predicted by the boundary theory. Finally we calculate some of the higher order corrections to the supergravity description of heterotic nonlinear sigma models.  [Show abstract] [Hide abstract]
ABSTRACT: We compute the quasinormal frequencies corresponding to the scalar sector of gravitational perturbations in the fourdimensional AdSSchwarzschild black hole by using the master field formalism of hepth/0305147. We argue that the nondeformation of the boundary metric favors a Robin boundary condition on the master field over the usual Dirichlet boundary condition mostly used in the literature. Using this Robin boundary condition we find a family of lowlying modes, whose frequencies match closely with predictions from linearized hydrodynamics on the boundary. In addition to the lowlying modes, we also see the usual sequence of modes with frequencies almost following an arithmetic progression. Comment: 23 pages, 3 figures; v2: typos corrected; v3: algebraic derivation of hydrodynamic modes corrected, results unaltered  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the beta function of nonlinear sigma models with SD+1 and AdSD+1 target spaces in a 1/D expansion up to order 1/D2 and to all orders in α′. This beta function encodes partial information about the spacetime effective action for the heterotic string to all orders in α′. We argue that a zero of the beta function, corresponding to a worldsheet CFT with AdSD+1 target space, arises from competition between the oneloop and higherloop terms, similarly to the bosonic and supersymmetric cases studied previously in [J.J. Friess, S.S. Gubser, Nonlinear sigma models with antide Sitter target spaces, Nucl. Phys. B 750 (2006) 111–141]. Various critical exponents of the nonlinear sigma model are calculated, and checks of the calculation are presented.  [Show abstract] [Hide abstract]
ABSTRACT: We compute the gravitational quasinormal modes of the global AdS_5Schwarzschild solution. We show how to use the holographic dual of these modes to describe a thermal plasma of finite extent expanding in a slightly anisotropic fashion. We compare these flows with the behavior of quarkgluon plasmas produced in relativistic heavy ion collisions by estimating the elliptic flow coefficient and the thermalization time. Comment: 59 pages, 6 figures. v2: corrected linearized hydro treatment, refs added  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the stability against small deformations of strings dangling into AdS_5Schwarzschild from a moving heavy quarkantiquark pair. We speculate that emission of massive string states may be an important part of the evolution of certain unstable configurations. Comment: 14 pages, 4 figures  [Show abstract] [Hide abstract]
ABSTRACT: Using AdS/CFT, we compute the Fourier space profile of ⟨tr F2⟩ generated by a heavy quark moving through a thermal plasma of strongly coupled 𝒩 = 4 superYangMills theory. We find evidence of directional emission from the quark whose description includes gauge fields with large momenta. We comment on the possible relevance of our results to relativistic heavy ion collisions.  [Show abstract] [Hide abstract]
ABSTRACT: We develop the linear equations that describe graviton perturbations of AdS_5Schwarzschild generated by a string trailing behind an external quark moving with constant velocity. Solving these equations allows us to evaluate the stress tensor in the boundary gauge theory. Components of the stress tensor exhibit directional structures in Fourier space at both large and small momentum. We comment on the possible relevance of our results to relativistic heavy ion collisions. 
Chapter: Improved holographic QCD
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ABSTRACT: We provide a review to holographic models based on Einsteindilaton gravity with a potential in five dimensions. Such theories, for a judicious choice of potential are very close to the physics of largeN YM theory both at zero and finite temperature. The zero temperature glueball spectra as well as their finite temperature thermodynamic functions compare well with lattice data. The model can be used to calculate transport coefficients, like bulk viscosity, the drag force and jet quenching parameters, relevant for the physics of the Quark–Gluon Plasma.
Publication Stats
502  Citations  
56.43  Total Impact Points  
Top Journals
Institutions

19702011

Purdue University
 Department of Physics
West Lafayette, IN, United States


2009

French National Centre for Scientific Research
Lutetia Parisorum, ÎledeFrance, France


2006

Princeton University
 Department of Physics
Princeton, New Jersey, United States
