465 research outputs found
Color filamentation in ultrarelativistic heavy-ion collisions
We study color fluctuations in the quark-gluon plasma produced at the early
stage of nucleus-nucleus collision at RHIC or LHC. The fluctuating color
current, which flows along the beam, can be very {\it large} due to the strong
anisotropy of the parton momentum distribution. A specific fluctuation, which
splits the parton system into the current filaments parallel to the beam
direction, is argued to grow exponentially. The physical mechanism responsible
for the phenomenon, which is known as a filamentation instability, is
discussed.Comment: 4 pages, no macro
Generalizing Phi-measure of event-by-event fluctuations in high-energy heavy-ion collisions
The Phi-measure of event-by-event fluctuations in high-energy heavy-ion
collisions corresponds to the second moment of the fluctuating quantity
distribution of interest. It is shown that the measure based on the third
moment preserves the properties of Phi but those related to the higher moments
do not. In particular, only the second and third moment measures are intensive
as thermodynamic quantities. The Phi_2- and Phi_3-measure of p_T-fluctuations
are computed for the hadron gas in equilibrium and the results are analyzed in
context of the experimental data.Comment: 6 pages, 2 figures, minor corrections, to appear in Phys. Lett.
Hard-loop dynamics of non-abelian plasma instabilities
I discuss recent advances in the understanding of non-equilibrium gauge field
dynamics in plasmas which have particle distributions which are locally
anisotropic in momentum space. In contrast to locally isotropic plasmas such
anisotropic plasmas have a spectrum of soft unstable modes which are
characterized by exponential growth of transverse (chromo)-magnetic fields at
short times. The long-time behavior of such instabilities depends on whether or
not the gauge group is abelian or non-abelian. Here I will report on recent
numerical simulations which attempt to determine the long-time behavior of an
anisotropic non-abelian plasma within hard-loop effective theory.Comment: 4 pages, 1 figure; Contribution to proceedings of Quark Matter 2005,
Budapest, Hungary, Aug 4-9 200
Chromodynamic Weibel instabilities in relativistic nuclear collisions
Employing a previously derived formulation, and extending the treatment from
purely transverse modes to wave vectors having a longitudinal component, we
discuss the prospects for the occurrence of Weibel-type color-current
filamentation in high-energy nuclear collisions. Numerical solutions of the
dispersion equation for a number of scenarios relevant to RHIC and LHC suggest
that modes with (predominantly transverse) wave numbers of several hundred MeV
may become moderately agitated during the early collision stage. The emergence
of filamentation helps to speed up the equilibration of the parton plasma and
it may lead to non-statistical azimuthal patterns in the hadron final state.Comment: 11 pages, RevTex, 13 (e)ps files (revised for PRC
Quasiquarks in two stream system
We study the collective quark excitations in an extremely anisotropic system
of two interpenetrating streams of the quark-gluon plasma. In contrast to the
gluon modes, all quark ones appear to be stable in such a system. Even more,
the quark modes in the two-stream system are very similar to those in the
isotropic plasma.Comment: 4 pages, 2 figures, minor corrections, to appear in Phys. Rev.
Density Fluctuations in the Quark-Gluon Plasma
Using the kinetic theory we discuss how the particle and energy densities of
the quark-gluon plasma fluctuate in a space-time cell. The fluctuations in the
equilibrium plasma and in that one from the early stage of ultrarelativistic
heavy-ion collisions are estimated. Within the physically interesting values of
the parameters involved the fluctuations appear sizeable in both cases.Comment: 8 pages, no macro
Sum rule of the correlation function
We derive a sum rule satisfied by the correlation function of two particles
with small relative momenta, which results from the completeness condition of
the quantum states.Comment: 6 pages, no macro
Momentum Broadening of a Fast Parton in a Perturbative Quark-Gluon Plasma
The average transverse momentum transfer per unit path length to a fast
parton scattering elastically in a perturbative quark-gluon plasma is related
to the radiative energy loss of the parton. We first calculate the momentum
transfer coefficient in terms of a classical Langevin problem and then
define it quantum-mechanically through scattering matrix element. After
treating the well known case of a quark-gluon plasma in equilibrium we consider
an off-equilibrium unstable plasma. As a specific example, we treat the
two-stream plasma with unstable modes of longitudinal chromoelectric field. In
the presence of the instabilities, is shown to exponentially grow in
time.Comment: Updated version containing an analysis of insufficiencies in previous
calculations of momentum broadening in unstable plasma
Chemical fluctuations in high-energy nuclear collisions
Fluctuations of the chemical composition of the hadronic system produced in
nuclear collisions are discussed using the measure which has been
earlier applied to study the transverse momentum fluctuations. The measure is
expressed through the moments of the multiplicity distribution and then the
properties of are discussed within a few models of multiparticle
production. A special attention is paid to the fluctuations in the equilibrium
ideal quantum gas. The system of kaons and pions, which is particularly
interesting from the experimental point of view, is discussed in detail.Comment: 8 pages, 4 figures, revised version to appear in Phys. Lett.
Chromodynamic Fluctuations in Quark-Gluon Plasma
Fluctuations of chromodynamic fields in the collisionless quark-gluon plasma
are found as a solution of the initial value linearized problem. The plasma
initial state is on average colorless, stationary and homogeneous. When the
state is stable, the initial fluctuations decay exponentially and in the
long-time limit a stationary spectrum of fluctuations is established. For the
equilibrium plasma it reproduces the spectrum which is provided by the
fluctuation-dissipation relation. Fluctuations in the unstable plasma, where
the memory of initial fluctuations is not lost, are also discussed.Comment: 19 pages, numerous but minor corrections, to appear in Phys. Rev.
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