14 research outputs found
The stress tensor of a quark moving through N=4 thermal plasma
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.Comment: 33 pages, 5 figures. v2: improved low K discussion; other minor
improvement
Stability of strings binding heavy-quark mesons
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 figure
Low-lying gravitational modes in the scalar sector of the global AdS_4 black hole
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 unaltere
Entanglement entropy of two dimensional systems and holography
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.Comment: 20 pages, 1 figure: v2 typos fixed, references and comments adde
Dissipation from a heavy quark moving through N=4 super-Yang-Mills plasma
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 structure
Heterotic non-linear sigma models with anti-de Sitter target spaces
We calculate the beta function of non-linear sigma models with S^{D+1} and
AdS_{D+1} target spaces in a 1/D expansion up to order 1/D^2 and to all orders
in \alpha'. This beta function encodes partial information about the spacetime
effective action for the heterotic string to all orders in \alpha'. We argue
that a zero of the beta function, corresponding to a worldsheet CFT with
AdS_{D+1} target space, arises from competition between the one-loop and
higher-loop terms, similarly to the bosonic and supersymmetric cases studied
previously in hep-th/0512355. Various critical exponents of the non-linear
sigma model are calculated, and checks of the calculation are presented.Comment: 36 pages, 7 figure
Shock waves in strongly coupled plasmas
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
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 the penetration depth
scales as . 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 adde