Georgios Michalogiorgakis

Publications (8)5.83 Total impact

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  Available from: ArXiv

  Article: Shock waves in strongly coupled plasmas II

  Sergei Khlebnikov, Martin Kruczenski, Georgios Michalogiorgakis
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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. KeywordsGauge-gravity correspondence–AdS-CFT Correspondence–Holography and quark-gluon plasmas
  Journal of High Energy Physics 04/2012; 2011(7):1-34. · 5.83 Impact Factor
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  Available from: ArXiv

  Article: Shock waves in strongly coupled plasmas

  Sergei Khlebnikov, Martin Kruczenski, Georgios Michalogiorgakis
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  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 $\ell\sim (1-v^2)^{1/4}$. We compare the results with second order hydrodynamics and the Israel-Stewart 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
  04/2010;
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  Available from: arxiv.org

  Article: Low-lying gravitational modes in the scalar sector of the global AdS_4 black hole

  Georgios Michalogiorgakis, Silviu S. Pufu
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  ABSTRACT: We compute the quasinormal frequencies corresponding to the scalar sector of gravitational perturbations in the four-dimensional AdS-Schwarzschild black hole by using the master field formalism of hep-th/0305147. We argue that the non-deformation 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 low-lying modes, whose frequencies match closely with predictions from linearized hydrodynamics on the boundary. In addition to the low-lying 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
  12/2006;
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  Available from: arxiv.org

  Article: Expanding plasmas and quasinormal modes of anti-de Sitter black holes

  Joshua J. Friess, Steven S. Gubser, Georgios Michalogiorgakis, Silviu S. Pufu
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  ABSTRACT: We compute the gravitational quasinormal modes of the global AdS_5-Schwarzschild 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 quark-gluon 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
  10/2006;
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  Available from: arxiv.org

  Article: Stability of strings binding heavy-quark mesons

  Joshua J. Friess, Steven S. Gubser, Georgios Michalogiorgakis, Silviu S. Pufu
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  ABSTRACT: We investigate the stability against small deformations of strings dangling into AdS_5-Schwarzschild from a moving heavy quark-anti-quark 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
  09/2006;
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  Available from: ArXiv

  Article: The stress tensor of a quark moving through N=4 thermal plasma

  Joshua J. Friess, Steven S. Gubser, Georgios Michalogiorgakis, Silviu S. Pufu
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  ABSTRACT: We develop the linear equations that describe graviton perturbations of AdS_5-Schwarzschild 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.
  08/2006;
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  Available from: ArXiv

  Article: Dissipation from a heavy quark moving through N=4 super-Yang-Mills plasma

  Joshua J. Friess, Steven S. Gubser, Georgios Michalogiorgakis
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  ABSTRACT: Using AdS/CFT, we compute the Fourier space profile of generated by a heavy quark moving through a thermal plasma of strongly coupled N=4 super-Yang-Mills theory. We find evidence of a wake whose description includes gauge fields with large momenta. We comment on the possible relevance of our results to relativistic heavy ion collisions. Comment: 17 pages, 2 figures. v2: reference added, other minor improvements. v3: improved the phrasing describing directional structures
  05/2006;
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  Available from: arxiv.org

  Article: Heterotic non-linear sigma models with anti-de Sitter target spaces

  Georgios Michalogiorgakis, Steven S. Gubser
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  ABSTRACT: We calculate the beta function of non-linear 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 one-loop and higher-loop terms, similarly to the bosonic and supersymmetric cases studied previously in [J.J. Friess, S.S. Gubser, Non-linear sigma models with anti-de Sitter target spaces, Nucl. Phys. B 750 (2006) 111–141]. Various critical exponents of the non-linear sigma model are calculated, and checks of the calculation are presented.
  Nuclear Physics B.