872 research outputs found
Interference Phenomena in Medium Induced Radiation
We consider the interference pattern for the medium-induced gluon radiation
produced by a color singlet quark-antiquark antenna embedded in a QCD medium
with size and `jet quenching' parameter . Within the BDMPS-Z
regime, we demonstrate that, for a dipole opening angle , the interference between the
medium--induced gluon emissions by the quark and the antiquark is suppressed
with respect to the direct emissions. This is so since direct emissions are
delocalized throughout the medium and thus yield contributions proportional to
while interference occurs only between emissions at early times, when both
sources remain coherent. Thus, for \tqq \gg\theta_c, the medium-induced
radiation is the sum of the two spectra individually produced by the quark and
the antiquark, without coherence effects like angular ordering. For \tqq
\ll\theta_c, the medium--induced radiation vanishes.Comment: 4 pages, 2 figures; Proceedings of the "Quark Matter 2011" conferenc
A New Mechanism of Quark Energy Loss
We show that a heavy quark moving sufficiently fast through a quark-gluon
plasma may lose energy by Cherenkov-radiating mesons. We demonstrate that this
takes place in all strongly coupled, large-Nc plasmas with a gravity dual. The
energy loss is exactly calculable in these models despite being an
O(1/Nc)-effect. We discuss phenomenological implications for heavy-ion
collision experiments.Comment: 4 pages, 4 figures; v2: plot modified, conclusions unchange
Prediction of a Photon Peak in Heavy Ion Collisions
We show that if a flavour-less vector meson remains bound after
deconfinement, and if its limiting velocity in the quark-gluon plasma is
subluminal, then this meson produces a distinct peak in the spectrum of thermal
photons emitted by the plasma. We also demonstrate that this effect is a
universal property of all strongly coupled, large-Nc plasmas with a gravity
dual. For the J/psi the corresponding peak lies between 3 and 5 GeV and could
be observed at LHC.Comment: 4 pages, 5 figures. Minor corrections; references adde
Angular Dependence of Jet Quenching Indicates Its Strong Enhancement Near the QCD Phase Transition
We study dependence of jet quenching on matter density, using "tomography" of
the fireball provided by RHIC data on azimuthal anisotropy of high
hadron yield at different centralities. Slicing the fireball into shells with
constant (entropy) density, we derive a "layer-wise geometrical limit"
which is indeed above the data . Interestingly, the
limit is reached only if quenching is dominated by shells with the entropy
density exactly in the near- region. We show two models that
simultaneously describe the high and data and conclude
that such a description can be achieved only if the jet quenching is few times
stronger in the near- region relative to QGP at . One possible
reason for that may be recent indications that the near- region is a
magnetic plasma of relatively light color-magnetic monopoles.Comment: 4 pages, 4 figures. Final version published as PRL102,202302(2009
Calculating the jet quenching parameter in the plasma of NCYM theory from gauge/gravity duality
A particular decoupling limit of non-extremal (D1, D3) brane bound state
system of type IIB string theory is known to give the gravity dual of
space-space non- commutative Yang-Mills (NCYM) theory at finite temperature. We
use a string probe in this background to compute the jet quenching parameter in
the strongly coupled plasma of hot non-commutative Yang-Mills theory in
(3+1)-dimensions from gauge/gravity duality. We give the expressions for the
jet quenching parameter for both small and large non-commutativity. For small
non-commutativity, we find that the value of the jet quenching parameter gets
reduced from its commutative value. The reduction is enhanced with temperature
as T^{7} for fixed non-commutativity and the fixed 't Hooft coupling. We
further generalize the results for the non-commutative Yang-Mills theories in
diverse dimensions.Comment: Latex file,12 pages,No figure; v2: 17 pages, Motivation, various
clarifications,references added. An estimation of the correction with the
known experimental bound on is given, v3: added more clarifications,
one reference and acknowledgment,version to appear in Phys. Rev.
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