502 research outputs found
Sound Mode Hydrodynamics from Bulk Scalar Fields
We study the hydrodynamic sound mode using gauge/gravity correspondence by
examining a generic black brane background's response to perturbations. We
assume that the background is generated by a single scalar field, and then
generalize to the case of multiple scalar fields. The relevant differential
equations obeyed by the gauge invariant variables are presented in both cases.
Finally, we present an analytical solution to these equations in a special
case; this solution allows us to determine the speed of sound and bulk
viscosity for certain special metrics. These results may be useful in
determining sound mode transport coefficients in phenomenologically motivated
holographic models of strongly coupled systems.Comment: 17 pages. Corrections made to one of the gauge invariant equations
(66). This equation was not used in the other main conclusions of the paper,
so the rest of the results are unchange
On Fluctuations of Conserved Charges : Lattice Results Versus Hadron Resonance Gas
We compare recent lattice results on fluctuations and correlations of
strangeness, baryon number and electric charge obtained with p4 improved
staggered action with the prediction of hadron resonance gas model. We show
that hadron resonance gas can describe these fluctuations reasonably well if
the hadron properties are as calculated on the lattice.Comment: 4 pages, LaTeX, uses jpconf.cls, to appear in the proceedings of 26th
Winter Workshop on Nuclear Dynamic
The applicability of causal dissipative hydrodynamics to relativistic heavy ion collisions
We utilize nonequilibrium covariant transport theory to determine the region
of validity of causal Israel-Stewart dissipative hydrodynamics (IS) and
Navier-Stokes theory (NS) for relativistic heavy ion physics applications. A
massless ideal gas with 2->2 interactions is considered in a 0+1D Bjorken
scenario, appropriate for the early longitudinal expansion stage of the
collision. In the scale invariant case of a constant shear viscosity to entropy
density ratio eta/s ~ const, we find that Israel-Stewart theory is 10% accurate
in calculating dissipative effects if initially the expansion timescale exceeds
half the transport mean free path tau0/lambda0 > ~2. The same accuracy with
Navier-Stokes requires three times larger tau0/lambda0 > ~6. For dynamics
driven by a constant cross section, on the other hand, about 50% larger
tau0/lambda0 > ~3 (IS) and ~9 (NS) are needed. For typical applications at RHIC
energies s_{NN}**(1/2) ~ 100-200 GeV, these limits imply that even the
Israel-Stewart approach becomes marginal when eta/s > ~0.15. In addition, we
find that the 'naive' approximation to Israel-Stewart theory, which neglects
products of gradients and dissipative quantities, has an even smaller range of
applicability than Navier-Stokes. We also obtain analytic Israel-Stewart and
Navier-Stokes solutions in 0+1D, and present further tests for numerical
dissipative hydrodynamics codes in 1+1, 2+1, and 3+1D based on generalized
conservation laws.Comment: 30 pages, 26 EPS figures, revtex stylefil
Elliptic flow in nuclear collisions at the Large Hadron Collider
We use perfect-fluid hydrodynamical model to predict the elliptic flow
coefficients in Pb + Pb collisions at the Large Hadron Collider (LHC). The
initial state for the hydrodynamical calculation for central collisions
is obtained from the perturbative QCD + saturation (EKRT) model. The centrality
dependence of the initial state is modeled by the optical Glauber model. We
show that the baseline results obtained from the framework are in good
agreement with the data from the Relativistic Heavy Ion Collider (RHIC), and
show predictions for the spectra and elliptic flow of pions in Pb + Pb
collisions at the LHC. Also mass and multiplicity effects are discussed.Comment: 11 pages, 10 figure
Dynamical freeze-out condition in ultrarelativistic heavy ion collisions
We determine the decoupling surfaces for the hydrodynamic description of
heavy ion collisions at RHIC and LHC by comparing the local hydrodynamic
expansion rate with the microscopic pion-pion scattering rate. The pion
spectra for nuclear collisions at RHIC and LHC are computed by applying the
Cooper-Frye procedure on the dynamical-decoupling surfaces, and compared with
those obtained from the constant-temperature freeze-out surfaces. Comparison
with RHIC data shows that the system indeed decouples when the expansion rate
becomes comparable with the pion scattering rate. The dynamical decoupling
based on the rates comparison also suggests that the effective decoupling
temperature in central heavy ion collisions remains practically unchanged from
RHIC to LHC.Comment: 7 pages, 9 figure
Influence of a temperature-dependent shear viscosity on the azimuthal asymmetries of transverse momentum spectra in ultrarelativistic heavy-ion collisions
We study the influence of a temperature-dependent shear viscosity over
entropy density ratio , different shear relaxation times , as
well as different initial conditions on the transverse momentum spectra of
charged hadrons and identified particles. We investigate the azimuthal flow
asymmetries as a function of both collision energy and centrality. The elliptic
flow coefficient turns out to be dominated by the hadronic viscosity at RHIC
energies. Only at higher collision energies the impact of the viscosity in the
QGP phase is visible in the flow asymmetries. Nevertheless, the shear viscosity
near the QCD transition region has the largest impact on the collective flow of
the system. We also find that the centrality dependence of the elliptic flow is
sensitive to the temperature dependence of .Comment: 13 pages, 20 figure
The Azimuthal Asymmetry at large p_t seem to be too large for a ``Jet Quenching''
We discuss simple generic model of ``jet quenching'' in which matter
absorption is defined by one parameter. We show that as absorption grows, the
azimuthal asymmetry v_2 grows as well, reaching the finite limit with a simple
geometric interpretation. It turns out, that this limit is still below the
experimental values for 6 > p_t > 2 GeV, according to preliminary data from
STAR experiment at RHIC. We thus conclude that ``jet quenching'' models alone
cannot account for the observed phenomenon, and speculate about alternative
scenarios.Comment: 3 pages, 2 figs, 1 table. The final version contaning note added in
proofs for PRC, which reflects experimental development which seem to suggest
that the geometrical model for v2 is in fact correct description of data at
pt=2-10 Ge
Second order hydrodynamics for a special class of gravity duals
The sound mode hydrodynamic dispersion relation is computed up to order
for a class of gravitational duals which includes both Schwarzschild and
Dp-Brane metrics. The implications for second order transport coefficients are
examined within the context of Israel-Stewart theory. These sound mode results
are compared with previously known results for the shear mode. This comparison
allows one to determine the third order hydrodynamic contributions to the shear
mode for the class of metrics considered here.Comment: 20 page
Isoäidit maahanmuuttajina Keskustelu Irina Antonovan, Eveline Fadayelin ja Maria Kirbasovan käännytyksistä Helsingin Sanomien välittämänä, toistamana ja rakentamana
v4: A small, but sensitive observable for heavy ion collisions
Higher order Fourier coefficients of the azimuthally dependent single
particle spectra resulting from noncentral heavy ion collisions are
investigated. For intermediate to large transverse momenta, these anisotropies
are expected to become as large as 5 %, and should be clearly measurable. The
physics content of these observables is discussed from two different extreme
but complementary viewpoints, hydrodynamics and the geometric limit with
extreme energy loss.Comment: as published: typos corrected, Fig. 3 slightly improved in numerics
and presentatio
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