1,916 research outputs found
QGP collective effects and jet transport
We present numerical simulations of the SU(2) Boltzmann-Vlasov equation
including both hard elastic particle collisions and soft interactions mediated
by classical Yang-Mills fields. We provide an estimate of the coupling of jets
to a hot isotropic plasma, which is independent of infrared cutoffs. In
addition, we investigate jet propagation in anisotropic plasmas, as created in
heavy-ion collisions. The broadening of jets is found to be stronger along the
beam line than in azimuth due to the creation of field configurations with
B_t>E_t and E_z>B_z via plasma instabilities.Comment: 4 pages, 5 figures. Presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 4-10 Feb 200
Jet broadening in unstable non-Abelian plasmas
We perform numerical simulations of the QCD Boltzmann-Vlasov equation
including both hard elastic particle collisions and soft interactions mediated
by classical Yang-Mills fields. We provide an estimate of the coupling of jets
to a hot plasma which is independent of infrared cutoffs. For weakly-coupled
anisotropic plasmas the local rotational symmetry in momentum space is broken.
The fields develop unstable modes, forming configurations where B_t>E_t and
E_z>B_z. This provides a possible explanation for the experimental observation
that high-energy jets traversing the plasma perpendicular to the beam axis
experience much stronger broadening in rapidity than in azimuth.Comment: 6 pages, 7 figures, version accepted for publication in Phys.Rev.C,
typos fixed, more detailed discussion of q-ha
Ultraviolet avalanche in anisotropic non-Abelian plasmas
We present solutions of coupled particle-field evolution in classical U(1)
and SU(2) gauge theories in real time on three-dimensional lattices. For
strongly anisotropic particle momentum distributions, we find qualitatively
different behavior for the two theories when the field strength is high enough
that non-Abelian self-interactions matter for SU(2). It appears that the energy
drained by a Weibel-like plasma instability from the particles does not build
up exponentially in transverse magnetic fields but instead returns,
isotropically, to the hard scale via a rapid avalanche into the ultraviolet.Comment: 22 pages, 10 figures; v3: small textual changes; updated to
correspond with version to appear in publicatio
A Comparative Study of Text Summarization Based on Synchronous and Asynchronous PSO
Text summarization is the process of extracting the most important sentences from the original document without its meaning change. The paper focus on Extractive summarization technique which chooses the important sentences from the document and integrates into summary. An extractive summarization technique, Particle swarm Optimization performs arithmetic operations that enhances a problem, by iteratively trying to improve possible solution with regard to input data. It determines a problem by having a population of possible solutions moving around the search space according to arithmetic formulae over the particles position and velocity. The sequence of modernized particles of PSO can be categorized into Synchronous PSO (S-PSO) and Asynchronous PSO(A-PSO). In synchronous PSO, after calculating the whole performance, velocities and positions of the particles are modernized, this increases the performance. In A-PSO after calculating its performance, velocities and positions of the particles are modernized using partial data which leads to extreme analysis. The comparative study on the synchronous PSO and asynchronous PSO with the precision and recall values for different datasets is considered. Asynchronous PSO has higher precision and recall values compared to synchronous PSO. Asynchronous PSO leads to extreme analysis of data
Pseudorapidity dependence of parton energy loss in relativistic heavy ion collisions
We analyze the recent data from the BRAHMS Collaboration on the
pseudorapidity dependence of nuclear modification factors in Au+Au collisions
at = 200 GeV by using the full three dimensional hydrodynamic
simulations for the density effects on parton energy loss. We first compute the
transverse spectra at and 2.2, and next take a ratio
, where is a nuclear
modification factor. It is shown that hydrodynamic components account for
at low and that quenched pQCD components lead
at high which are consistent with the data.
Strong suppression at is compatible with the parton energy loss in
the final state.Comment: 5 pages, 4 figures; one figure adde
Re-Hardening of Hadron Transverse Mass Spectra in Relativistic Heavy-Ion Collisions
We analyze the spectra of pions and protons in heavy-ion collisions at
relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented
hadron-string cascade model. In this energy region, hadron transverse mass
spectra first show softening until SPS energies, and re-hardening may emerge at
RHIC energies. Since hadronic matter is expected to show only softening at
higher energy densities, this re-hardening of spectra can be interpreted as a
good signature of the quark-gluon plasma formation.Comment: 10 pages, 3 figures, 1 table, Poster presentation at QM2001, Revised
to correct latex error in citation on April 6, 200
Thermalization and the chromo-Weibel instability
Despite the apparent success of ideal hydrodynamics in describing the
elliptic flow data which have been produced at Brookhaven National Lab's
Relativistic Heavy Ion Collider, one lingering question remains: is the use of
ideal hydrodynamics at times t < 1 fm/c justified? In order to justify its use
a method for rapidly producing isotropic thermal matter at RHIC energies is
required. One of the chief obstacles to early isotropization/thermalization is
the rapid longitudinal expansion of the matter during the earliest times after
the initial nuclear impact. As a result of this expansion the parton
distribution functions become locally anisotropic in momentum space. In
contrast to locally isotropic plasmas anisotropic plasmas have a spectrum of
soft unstable modes which are characterized by exponential growth of transverse
chromo-magnetic/-electric fields at short times. This instability is the QCD
analogue of the Weibel instability of QED. Parametrically the chromo-Weibel
instability provides the fastest method for generation of soft background
fields and dominates the short-time dynamics of the system.Comment: 8 pages, 4 figures, Invited plenary talk given at the 19th
International Conference on Ultrarelativistic Nucleus-Nucleus Collisions:
Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200
Branching ratio change in K- absorption at rest and the nature of the Lambda(1405)
We investigate in-medium corrections to the branching ratio in K- absorption
at rest and their effect on the (positively and negatively) charged pion
spectrum. The in-medium corrections are due to Pauli blocking, which arises if
the Lambda(1405) is assumed to be a -nucleon bound state and leads to
a density and momentum dependent mass shift of the Lambda(1405). Requiring that
the optical potential as well as the branching ratio are derived from the same
elementary T-matrix, we find that the in-medium corrected, density dependent
T-matrix gives a better description of the K- absorption reaction than the
free, density-independent one. This result suggests that the dominant component
of the Lambda(1405) wave function is the bound state.Comment: 8 Pages, Revtex with epsf, and embedded 8 ps figure
Electron transport in Coulomb- and tunnel-coupled one-dimensional systems
We develop a linear theory of electron transport for a system of two
identical quantum wires in a wide range of the wire length L, unifying both the
ballistic and diffusive transport regimes. The microscopic model, involving the
interaction of electrons with each other and with bulk acoustical phonons
allows a reduction of the quantum kinetic equation to a set of coupled
equations for the local chemical potentials for forward- and backward-moving
electrons in the wires. As an application of the general solution of these
equations, we consider different kinds of electrical contacts to the
double-wire system and calculate the direct resistance, the transresistance, in
the presence of tunneling and Coulomb drag, and the tunneling resistance. If L
is smaller than the backscattering length l_P, both the tunneling and the drag
lead to a negative transresistance, while in the diffusive regime (L >>l_P) the
tunneling opposes the drag and leads to a positive transresistance. If L is
smaller than the phase-breaking length, the tunneling leads to interference
oscillations of the resistances that are damped exponentially with L.Comment: Text 14 pages in Latex/Revtex format, 4 Postscript figure
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