955 research outputs found
The chromo-weibel instability
I discuss the physics of non-Abelian plasmas which are locally anisotropic in momentum space. Such momentum-space anisotropies are generated by the rapid longitudinal expansion of the matter created in the first 1 fm/c of an ultrarelativistic heavy ion collision. 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. The existence of the chromo-Weibel instability has been proven using diagrammatic methods, transport theory, and numerical solution of classical Yang-Mills fields. I review the results obtained from each of these methods and discuss the numerical techniques which are being used to determine the late-time behavior of plasmas subject to a chromo-Weibel instability
The chromo-Weibel instability
I discuss the physics of non-Abelian plasmas which are locally anisotropic in
momentum space. Such momentum-space anisotropies are generated by the rapid
longitudinal expansion of the matter created in the first 1 fm/c of an
ultrarelativistic heavy ion collision. 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. The existence of the chromo-Weibel
instability has been proven using diagrammatic methods, transport theory, and
numerical solution of classical Yang-Mills fields. I review the results
obtained from each of these methods and discuss the numerical techniques which
are being used to determine the late-time behavior of plasmas subject to a
chromo-Weibel instability.Comment: 5 pages, 4 figures; v2 one reference added, small changes to text;
Proceedings contribution for the International Symposium on Multiparticle
Dynamics, Paraty, Rio de Janeiro, Brazil, Sept 2-8, 2006; Invited tal
Recent progress in anisotropic hydrodynamics
The quark-gluon plasma created in a relativistic heavy-ion collisions
possesses a sizable pressure anisotropy in the local rest frame at very early
times after the initial nuclear impact and this anisotropy only slowly relaxes
as the system evolves. In a kinetic theory picture, this translates into the
existence of sizable momentum-space anisotropies in the underlying partonic
distribution functions, . In such cases, it is better to
reorganize the hydrodynamical expansion by taking into account momentum-space
anisotropies at leading-order in the expansion instead of as a perturbative
correction to an isotropic distribution. The resulting anisotropic
hydrodynamics framework has been shown to more accurately describe the dynamics
of rapidly expanding systems such as the quark-gluon plasma. In this
proceedings contribution, I review the basic ideas of anisotropic
hydrodynamics, recent progress, and present a few preliminary phenomenological
predictions for identified particle spectra and elliptic flow.Comment: 8 pages, 4 figures; Proceedings contribution for "12th Conference on
Quark Confinement and the Hadron Spectrum
Measuring Quark-Gluon-Plasma Thermalization Time with Dileptons
We calculate the medium dilepton yield from a quark-gluon plasma which has a
time-dependent local momentum-space anisotropy. A phenomenological model for
the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau),
is constructed which interpolates between free streaming behavior at early
times (tau >
tau_iso). We show that high-energy dilepton production is sensitive to the
assumed plasma isotropization time, tau_iso, and can therefore be used to
experimentally determine the time of onset for hydrodynamic expansion of a
quark-gluon plasma and the magnitude of expected early-time momentum-space
anisotropies.Comment: 4 pages, 5 figures; v3: update to match published versio
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