726 research outputs found
Third-order relativistic dissipative hydrodynamics
Following the procedure introduced by Israel and Stewart, we expand the
entropy current up to the third order in the shear stress tensor
and derive a novel third-order evolution equation for
. This equation is solved for the one-dimensional Bjorken
boost-invariant expansion. The scaling solutions for various values of the
shear viscosity to the entropy density ratio are shown to be in very
good agreement with those obtained from kinetic transport calculations. For the
pressure isotropy starting with 1 at , the third-order
corrections to Israel-Stewart theory are approximately 10\% for
and more than a factor of 2 for . We also estimate all higher-order
corrections to Israel-Stewart theory and demonstrate their importance in
describing highly viscous matters.Comment: Version published in Phys.Rev.C. 5 pages, 1 figur
Dissipative hydrodynamics for multi-component systems
Second-order dissipative hydrodynamic equations for each component of a
multi-component system are derived using the entropy principle. Comparison of
the solutions with kinetic transport results demonstrates validity of the
obtained equations. We demonstrate how the shear viscosity of the total system
can be calculated in terms of the involved cross sections and partial
densities. Presence of the inter-species interactions leads to a characteristic
time-dependence of the shear viscosity of the mixture, which also means that
the shear viscosity of a mixture cannot be calculated using the Green-Kubo
formalism the way it has been done recently. This finding is of interest for
understanding of the shear viscosity of a quark-gluon-plasme extracted from
comparisons of hydrodynamic simulations with experimental results from RHIC and
LHC.Comment: 5 pages, 3 figures. Submitted to EPJA topical issue on "Relativistic
Hydro- and Thermodynamics". arXiv admin note: text overlap with
arXiv:1103.403
Mechanical Properties Of Fluctuating Elastic Membranes Under Uni-Axial Tension
Atomically thin sheets, such as graphene, are widely used in nanotechnology.
Recently they have also been used in applications including kirigami and
self-folding origami, where it becomes important to understand how they respond
to external loads. Motivated by this, we investigate how isotropic sheets
respond to uniaxial tension by employing the self-consistent screening analysis
method and molecular dynamics simulations. Previously, it was shown that for
freely suspended sheets thermal fluctuations effectively renormalize elastic
constants, which become scale-dependent beyond a characteristic thermal length
scale (a few nanometers for graphene at room temperature), beyond which the
bending rigidity increases, while the in-plane elastic constants reduce with
universal power law exponents. For sheets under uniaxial tension,
, we find that beyond a stress-dependent length scale, the
effective in-plane elastic constants become strongly anisotropic and scale
differently along the axis of uni-axial stress and orthogonal to it. The
bending rigidities on the other hand will not exhibit any anomalous behavior
beyond this stress-dependent length scale. In addition, for moderate tensions
we find a universal non-linear stress-strain relation. For large uni-axial
tensions, the Young's modulus of the bare elastic material is recovered
QCD Matter Thermalization at RHIC and LHC
Employing the perturbative QCD inspired parton cascade, we investigate
kinetic and chemical equilibration of the partonic matter created in central
heavy ion collisions at RHIC and LHC energies. Two types of initial conditions
are chosen. One is generated by the model of wounded nucleons using the PYTHIA
event generator and Glauber geometry. Another is considered as a color glass
condensate. We show that kinetic equilibration is almost independent on the
chosen initial conditions, whereas there is a sensitive dependence for chemical
equilibration. The time scale of thermalization lies between 1 and 1.5 fm/c.
The final parton transverse energy obtained from BAMPS calculations is compared
with the RHIC data and is estimated for the LHC energy.Comment: 8 pages, 10 figures, plenary talk at International Conference on
Strangeness in Quark Matter 2008, Beijing, China, October 6-10, 200
Shear viscosity and out of equilibrium dynamics
Using Grad's method, we calculate the entropy production and derive a formula
for the second-order shear viscosity coefficient in a one-dimensionally
expanding particle system, which can also be considered out of chemical
equilibrium. For a one-dimensional expansion of gluon matter with Bjorken boost
invariance, the shear tensor and the shear viscosity to entropy density ratio
are numerically calculated by an iterative and self-consistent
prescription within the second-order Israel-Stewart hydrodynamics and by a
microscopic parton cascade transport theory. Compared with obtained
using the Navier-Stokes approximation, the present result is about 20% larger
at a QCD coupling (with ) and is a
factor of 2-3 larger at a small coupling . We demonstrate
an agreement between the viscous hydrodynamic calculations and the microscopic
transport results on , except when employing a small . On the
other hand, we demonstrate that for such small , the gluon system is
far from kinetic and chemical equilibrium, which indicates the break down of
second-order hydrodynamics because of the strong noneqilibrium evolution. In
addition, for large (), the Israel-Stewart hydrodynamics
formally breaks down at large momentum GeV but is still a
reasonably good approximation.Comment: Title and text updated. Published versio
RHIC and LHC phenomena with an unified parton transport
We discuss recent applications of the partonic pQCD based cascade model BAMPS with focus on heavy-ion phenomeneology in hard and soft momentum range. The nuclear modification factor as well as elliptic flow are calculated in BAMPS for RHIC end LHC energies. These observables are also discussed within the same framework for charm and bottom quarks. Contributing to the recent jet-quenching investigations we present first preliminary results on application of jet reconstruction algorithms in BAMPS. Finally, collective effects induced by jets are investigated: we demonstrate the development of Mach cones in ideal matter as well in the highly viscous regime
Relativistic shock waves and Mach cones in viscous gluon matter
To investigate the formation and the propagation of relativistic shock waves in viscous gluon matter we solve the relativistic Riemann problem using a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio n/s. Furthermore we compare our results with those obtained by solving the relativistic causal dissipative fluid equations of Israel and Stewart (IS), in order to show the validity of the IS hydrodynamics. Employing the parton cascade we also investigate the formation of Mach shocks induced by a high-energy gluon traversing viscous gluon matter. For n/s = 0.08 a Mach cone structure is observed, whereas the signal smears out for n/s >=0.32
Shear viscosity and out of equilibrium dynamics
Using Grad's method, we calculate the entropy production and derive a formula
for the second-order shear viscosity coefficient in a one-dimensionally
expanding particle system, which can also be considered out of chemical
equilibrium. For a one-dimensional expansion of gluon matter with Bjorken boost
invariance, the shear tensor and the shear viscosity to entropy density ratio
are numerically calculated by an iterative and self-consistent
prescription within the second-order Israel-Stewart hydrodynamics and by a
microscopic parton cascade transport theory. Compared with obtained
using the Navier-Stokes approximation, the present result is about 20% larger
at a QCD coupling (with ) and is a
factor of 2-3 larger at a small coupling . We demonstrate
an agreement between the viscous hydrodynamic calculations and the microscopic
transport results on , except when employing a small . On the
other hand, we demonstrate that for such small , the gluon system is
far from kinetic and chemical equilibrium, which indicates the break down of
second-order hydrodynamics because of the strong noneqilibrium evolution. In
addition, for large (), the Israel-Stewart hydrodynamics
formally breaks down at large momentum GeV but is still a
reasonably good approximation.Comment: Title and text updated. Published versio
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