136 research outputs found
Comments on the String dual to N=1 SQCD
We study the String dual to N=1 SQCD deformed by a quartic superpotential in
the quark superfields. We present a unified view of the previous results in the
literature and find new exact solutions and new asymptotic solutions. Then we
study the Physics encoded in these backgrounds, giving among other things a
resolution to an old puzzle related to the beta function and a sufficient
criteria for screening. We also extend our results to the SO(Nc) case where we
present a candidate for the Wilson loop in the spinorial representation.
Various aspects of this line of research are critically analyzed.Comment: 50 pages plus appendixes. Three figures and two table
AdS black holes as reflecting cavities
We use the identification between null singularities of correlators in the
bulk with time singularities in the boundary correlators to study the analytic
structure of time-dependent thermal Green functions using the eikonal
approximation for classical solutions in the AdS black hole background. We show
that the location of singularities in complex time can be understood in terms
of null rays bouncing on the boundaries and singularities of the eternal black
hole, giving the picture of a `reflecting cavity'. We can then extract the
general analytic expression for the asymptotic values of the frequencies of
quasinormal modes in large AdS black holes.Comment: 14 pages, 2 figures, reference adde
Knotted solutions for linear and nonlinear theories: Electromagnetism and fluid dynamics
We examine knotted solutions, the most simple of which is the “Hopfion”, from the point of view of relations between electromagnetism and ideal fluid dynamics. A map between fluid dynamics and electromagnetism works for initial conditions or for linear perturbations, allowing us to find new knotted fluid solutions. Knotted solutions are also found to be solutions of nonlinear generalizations of electromagnetism, and of quantum-corrected actions for electromagnetism coupled to other modes. For null configurations, electromagnetism can be described as a null pressureless fluid, for which we can find solutions from the knotted solutions of electromagnetism. We also map them to solutions of Euler's equations, obtained from a type of nonrelativistic reduction of the relativistic fluid equations
Hydrodynamics and beyond in the strongly coupled N=4 plasma
We continue our investigations on the relation between hydrodynamic and
higher quasinormal modes in the AdS black hole background started in
arXiv:0710.4458 [hep-th]. As is well known, the quasinormal modes can be
interpreted as the poles of the retarded Green functions of the dual N=4 gauge
theory at finite temperature. The response to a generic perturbation is
determined by the residues of the poles. We compute these residues numerically
for energy-momentum and R-charge correlators. We find that the diffusion modes
behave in a similar way: at small wavelengths the residues go over into a form
of a damped oscillation and therefore these modes decouple at short distances.
The sound mode behaves differently: its residue does not decay and at short
wavelengths this mode behaves as the higher quasinormal modes. Applications of
our findings include the definition of hydrodynamic length and time scales. We
also show that the quasinormal modes, including the hydrodynamic diffusion
modes, obey causality.Comment: 29 pages, 11 figure
A note on the velocity of holographic long-lived mesons
We study fluctuations of a U(1) gauge field on the worldvolume of Nf probe
D7-branes in the background of Nc black D3-branes with a finite baryon density.
The choice of mode corresponds to vector mesons in the dual gauge theory whose
mass and lifetime can be determined by a study of the quasinormal modes. The
speed of propagation of these holographic mesons at large momenta is studied
from the dispersion relations of the quasinormal modes of the system.Comment: 4 pages, 2 figure
Wilson loops in warped resolved deformed conifolds
We calculate quark-antiquark potentials using the relationship between the
expectation value of the Wilson loop and the action of a probe string in the
string dual. We review and categorize the possible forms of the dependence of
the energy on the separation between the quarks. In particular, we examine the
possibility of there being a minimum separation for probe strings which do not
penetrate close to the origin of the bulk space, and derive a condition which
determines whether this is the case. We then apply these considerations to the
flavoured resolved deformed conifold background of Gaillard et al. We suggest
that the unusual behaviour we observe in this solution is likely to be related
to the IR singularity which is not present in the unflavoured case
Heavy Quarkonium States with the Holographic Potential
The quarkonium states in a quark-gluon plasma is examined with the heavy
quark potential implied by the holographic principle. Both the vanila
AdS-Schwarzschild metric and the one with an infrared cutoff are considered.
The dissociation temperature is calculated by solving the Schr\"o dinger
equation of the potential model. In the case of the AdS-Schwarzschild metric
with a IR cutoff, the dissociation temperatures for and
with the U-ansatz of the potential are found to agree with the lattice results
within a factor of two.Comment: 9 pages with 2 figues in Revte
Meson widths from string worldsheet instantons
We show that open strings living on a D-brane which lies outside an AdS black
hole can tunnel into the black hole through worldsheet instantons. These
instantons have a simple interpretation in terms of thermal quarks in the dual
Yang-Mills (YM) theory. As an application we calculate the width of a meson in
a strongly coupled quark-gluon plasma which is described holographically as a
massless mode on a D7 brane in AdS_5 \times S_5. While the width of the meson
is zero to all orders in the 1/\sqrt{\lambda} expansion with \lambda the 't
Hooft coupling, it receives non-perturbative contributions in 1/\sqrt{\lambda}
from worldsheet instantons. We find that the width increases quadratically with
momentum at large momentum and comment on potential phenomenological
implications of this enhancement for heavy ion collisions. We also comment on
how this non-perturbative effect has important consequences for the phase
structure of the YM theory obtained in the classical gravity limit.Comment: 6 pages, 3 figure
On meson melting in the quark medium
We consider a heavy quark-antiquark pair as a heavy meson in the
medium composed of light quarks and gluons. By using the AdS/CFT
correspondence, the properties of this system are investigated. In particular,
we study the inter-quark distance and it is shown that the mechanism of melting
in the quark-gluon plasma and in the hadronic phase are the same. It is found
that by considering finite coupling corrections, the inter-quark distance of a
heavy meson decreases. As a result a heavy meson like will melt at
higher temperatures. By considering rotating heavy mesons, we discuss melting
of exited states like and .Comment: 18 pages, 12 figures, We more clarify and extend the results of
arXiv:0907.006
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