295 research outputs found
A Weibel Instability in the Melting Color Glass Condensate
Based on hep-ph/0510121, we discuss further the numerical study of classical
SU(2) 3+1-D Yang-Mills equations for matter produced in a high energy heavy ion
collision. The growth of the amplitude of fluctuations as (where is a scale arising from the saturation of
gluons in the nuclear wavefunction) is shown to be robust over a wide range of
initial amplitudes that violate boost invariance. We argue that this growth is
due to a non-Abelian Weibel instability, the scale of which is set by a
dynamically generated plasmon mass. We find good agreement when we relate
to the prediction from kinetic theory.Comment: 8 pages, invited talk at Workshop on Quark Gluon Plasma
Thermalization, Vienna, August 10th-12th, 200
Collective non-Abelian instabilities in a melting Color Glass Condensate
We present first results for 3+1-D simulations of SU(2) Yang-Mills equations
for matter expanding into the vacuum after a heavy ion collision. Violations of
boost invariance cause a Weibel instability leading soft modes to grow with
proper time as , where is a
scale arising from the saturation of gluons in the nuclear wavefunction. The
scale for the growth rate is set by a plasmon mass, defined as
, generated dynamically
in the collision. We compare the numerical ratio to the
corresponding value predicted by the Hard Thermal Loop formalism for
anisotropic plasmas.Comment: 4 pages, 4 figures, revtex4; v2: typos corrected, discussion on
growth rate in expanding system added, accepted for publication in PR
Particle spectra and HBT radii for simulated central nuclear collisions of C+C, Al+Al, Cu+Cu, Au+Au, and Pb+Pb from Sqrt(s)=62.4-2760 GeV
We study the temperature profile, pion spectra and HBT radii in central
symmetric and boost-invariant nuclear collisions using a super hybrid model for
heavy-ion collisions (SONIC) combining pre-equilibrium flow with viscous
hydrodynamics and late-stage hadronic rescatterings. In particular, we simulate
Pb+Pb collisions at Sqrt(s)=2.76 TeV, Au+Au, Cu+Cu, Al+Al, and C+C collisions
at Sqrt(s)=200 GeV and Au+Au, Cu+Cu collisions at Sqrt(s)=62.4 GeV. We find
that SONIC provides a good match to the pion spectra and HBT radii for all
collision systems and energies, confirming earlier work that a combination of
pre-equilibrium flow, viscosity and QCD equation of state can resolve the
so-called HBT puzzle. For reference, we also show p+p collisions at Sqrt(s)=7
TeV. We make tabulated data for the 2+1 dimensional temperature evolution of
all systems publicly available for the use in future jet energy loss or similar
studies.Comment: 9 pages, 5 figures, 2 tables; v2: fixed typos, updated figures; v3:
minor changes, matches published versio
Tsunamis, Viscosity and the HBT Puzzle
The equation of state and bulk and shear viscosities are shown to be able to
affect the transverse dynamics of a central heavy ion collision. The net
entropy, along with the femtoscopic radii are shown to be affected at the
10-20% level by both shear and bulk viscosity. The degree to which these
effects help build a tsunami-like pulse is also discussed.Comment: Contribution to SQM 2007 in Levoca, Slovaki
A fully relativistic lattice Boltzmann algorithm
Starting from the Maxwell-Juettner equilibrium distribution, we develop a
relativistic lattice Boltzmann (LB) algorithm capable of handling
ultrarelativistic systems with flat, but expanding, spacetimes. The algorithm
is validated through simulations of quark-gluon plasma, yielding excellent
agreement with hydrodynamic simulations. The present scheme opens the
possibility of transferring the recognized computational advantages of lattice
kinetic theory to the context of both weakly and ultra-relativistic systems.Comment: 12 pages, 8 figure
Bjorken Flow, Plasma Instabilities, and Thermalization
At asymptotically high energies, thermalization in heavy ion collisions can
be described via weak-coupling QCD. We present a complete treatment of how
thermalization proceeds, at the parametric weak-coupling level. We show that
plasma instabilities dominate the dynamics, from immediately after the
collision until well after the plasma becomes nearly in equilibrium. Initially
they drive the system close to isotropy, but Bjorken expansion and increasing
diluteness makes the system again become more anisotropic. At time \tau ~
\alpha^(-12/5) Q^(-1) the dynamics become dominated by a nearly-thermal bath;
and at time \tau ~ \alpha^(-5/2) Q^(-1)$ the bath comes to dominate the energy
density, completing thermalization. After this time there is a nearly isotropic
and thermal Quark-Gluon Plasma.Comment: 22 pages, 5 figure
Collective modes of an Anisotropic Quark-Gluon Plasma II
We continue our exploration of the collective modes of an anisotropic quark
gluon plasma by extending our previous analysis to arbitrary Riemann sheets. We
demonstrate that in the presence of momentum-space anisotropies in the parton
distribution functions there are new relevant singularities on the neighboring
unphysical sheets. We then show that for sufficiently strong anisotropies that
these singularities move into the region of spacelike momentum and their effect
can extend down to the physical sheet. In order to demonstrate this explicitly
we consider the polarization tensor for gluons propagating parallel to the
anisotropy direction. We derive analytic expressions for the gluon structure
functions in this case and then analytically continue them to unphysical
Riemann sheets. Using the resulting analytic continuations we numerically
determine the position of the unphysical singularities. We then show that in
the limit of infinite contraction of the distribution function along the
anisotropy direction that the unphysical singularities move onto the physical
sheet and result in real spacelike modes at large momenta for all
"out-of-plane" angles of propagation.Comment: 13 pages, 8 figure
Nonspherically Symmetric Collapse in Asymptotically AdS Spacetimes
We numerically simulate gravitational collapse in asymptotically anti-de
Sitter spacetimes away from spherical symmetry. Starting from initial data
sourced by a massless real scalar field, we solve the Einstein equations with a
negative cosmological constant in five spacetime dimensions and obtain a family
of non-spherically symmetric solutions, including those that form two distinct
black holes on the axis. We find that these configurations collapse faster than
spherically symmetric ones of the same mass and radial compactness. Similarly,
they require less mass to collapse within a fixed time
Comment on and Erratum to "Pressure of Hot QCD at Large N_f"
We repeat and correct the recent calculation of the thermodynamic potential
of hot QCD in the limit of large number N_f of fermions. The new result for the
thermal pressure turns out to agree significantly better with results obtained
from perturbation theory at small coupling. For large coupling, a nonmonotonic
behaviour is reproduced, but the pressure of the strongly coupled theory does
not exceed the free pressure as long as the Landau pole ambiguity remains
negligible numerically.Comment: 9 pages, 3 figures, JHEP3; v2: version accepted for publication in
JHEP (title changed, 1 footnote added, 1 reference updated, content otherwise
unchanged
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