171 research outputs found
Drag force in a string model dual to large-N QCD
We compute the drag force exerted on a quark and a di-quark systems in a
background dual to large-N QCD at finite temperature. We find that appears a
drag force in the former setup with flow of energy proportional to the mass of
the quark while in the latter there is no dragging as in other studies. We also
review the screening length.Comment: 15 pages, typos removed, error corrected, refs adde
No-Drag String Configurations for Steadily Moving Quark-Antiquark Pairs in a Thermal Bath
We investigate the behavior of stationary string configurations on a
five-dimensional AdS black hole background which correspond to quark-antiquark
pairs steadily moving in an N=4 super Yang-Mills thermal bath. There are many
branches of solutions, depending on the quark velocity and separation as well
as on whether Euclidean or Lorentzian configurations are examined.Comment: references added; statements corrected; eliminated computation of jet
quenching parameter from Wilson loop of [Liu, Rajagopal, Wiedemann,
hep-th/0605178] using Euclidean string configurations since those authors
advocate [hep-th/0607062, footnote 14] the use of spacelike Lorentzian string
configurations instea
Drag Force in a Charged N=4 SYM Plasma
Following recent developments, we employ the AdS/CFT correspondence to
determine the drag force exerted on an external quark that moves through an N=4
super-Yang-Mills plasma with a non-zero R-charge density (or, equivalently, a
non-zero chemical potential). We find that the drag force is larger than in the
case where the plasma is neutral, but the dependence on the charge is
non-monotonic.Comment: 16 pages, 1 eps figure; v2: references added, typos fixed; v3: more
general ansatz, new nontrivial solution obtained, nonmonotonicity of the drag
force made explicit in new figure, version to appear in JHE
Drag force in SYM plasma with B field from AdS/CFT
We investigate drag force in a thermal plasma of N=4 super Yang-Mills theory
via both fundamental and Dirichlet strings under the influence of non-zero NSNS
-field background. In the description of AdS/CFT correspondence the endpoint
of these strings correspondes to an external monopole or quark moving with a
constant electromagnetic field. We demonstrate how the configuration of string
tail as well as the drag force obtains corrections in this background.Comment: 13 pages, 2 figures, more discussion and reference adde
The Energy of a Moving Quark-Antiquark Pair in an N=4 SYM Plasma
We make use of the AdS/CFT correspondence to determine the energy of an
external quark-antiquark pair that moves through strongly-coupled thermal N=4
super-Yang-Mills plasma, both in the rest frame of the plasma and in the rest
frame of the pair. It is found that the pair feels no drag force, has an energy
that reproduces the expected 1/L (or gamma/L) behavior at small quark-antiquark
separations, and becomes unbound beyond a certain screening length whose
velocity-dependence we determine. We discuss the relation between the
high-velocity limit of our results and the lightlike Wilson loop proposed
recently as a definition of the jet-quenching parameter.Comment: LaTeX 2e, 27 pages, 8 eps figures; v2: added computation of the pair
energy in the plasma rest frame, clarified the comparison with
hep-ph/0607062, corrected typos, added reference
Energy Loss of Gluons, Baryons and k-Quarks in an N=4 SYM Plasma
We consider different types of external color sources that move through a
strongly-coupled thermal N=4 super-Yang-Mills plasma, and calculate, via the
AdS/CFT correspondence, the dissipative force (or equivalently, the rate of
energy loss) they experience. A bound state of k quarks in the totally
antisymmetric representation is found to feel a force with a nontrivial
k-dependence. Our result for k=1 (or k=N-1) agrees at large N with the one
obtained recently by Herzog et al. and Gubser, but contains in addition an
infinite series of 1/N corrections. The baryon (k=N) is seen to experience no
drag. Finally, a heavy gluon is found to be subject to a force which at large N
is twice as large as the one experienced by a heavy quark, in accordance with
gauge theory expectations.Comment: Latex 2e, 24 pages, 1 eps figure; v2: slightly amplified discussion
on the relation between the drag force and the tension of a spatial Wilson
loop; v3: minor changes, version to appear in JHE
Spacelike strings and jet quenching from a Wilson loop
We investigate stationary string solutions with spacelike worldsheet in a
five-dimensional AdS black hole background, and find that there are many
branches of such solutions. Using a non-perturbative definition of the jet
quenching parameter proposed by Liu et. al., hep-ph/0605178, we take the
lightlike limit of these solutions to evaluate the jet quenching parameter in
an N=4 super Yang-Mills thermal bath. We show that this proposed definition
gives zero jet quenching parameter, independent of how the lightlike limit is
taken. In particular, the minimum-action solution giving the dominant
contribution to the Wilson loop has a leading behavior that is linear, rather
than quadratic, in the quark separation.Comment: 38 pages, 6 figures, statements correcte
A systematic study of J/psi suppression in cold nuclear matter
Based on a Glauber model, a statistical analysis of all mid-rapidity J/psi
hadroproduction and leptoproduction data on nuclear targets is carried out.
This allows us to determine the J/psi-nucleon inelastic cross section, whose
knowledge is crucial to interpret the J/psi suppression observed in heavy-ion
collisions, at SPS and at RHIC. The values of sigma are extracted from each
experiment. A clear tension between the different data sets is reported. The
global fit of all data gives sigma=3.4+/-0.2 mb, which is significantly smaller
than previous estimates. A similar value, sigma=3.5+/-0.2 mb, is obtained when
the nDS nuclear parton densities are included in the analysis, although we
emphasize that the present uncertainties on gluon (anti)shadowing do not allow
for a precise determination of sigma. Finally, no significant energy dependence
of the J/psi-N interaction is observed, unless strong nuclear modifications of
the parton densities are assumed.Comment: 25 pages, 5 figure
Calculating the jet-quenching parameter in STU background
In this paper we use the AdS/CFT correspondence to compute the jet-quenching
parameter in a N=2 thermal plasma. We consider the general three-charge black
hole and discuss some special cases. We add a constant electric field to the
background and find the effect of the electric field on the jet-quenching
parameter. Also we include higher derivative terms and obtain the first-order
correction for the jet-quenching parameter.Comment: 17 pages, 3 figures, revised versio
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