8,258 research outputs found
Review of the "Bottom-Up" scenario
Thermalization of a longitudinally expanding color glass condensate with
Bjorken boost invariant geometry is investigated within parton cascade BAMPS.
Our main focus lies on the detailed comparison of thermalization, observed in
BAMPS with that suggested in the Bottom-Up scenario. We demonstrate that the
tremendous production of soft gluons via , which is shown in the
Bottom-Up picture as the dominant process during the early preequilibration,
will not occur in heavy ion collisions at RHIC and LHC energies, because the
back reaction hinders the absolute particle multiplication.
Moreover, contrary to the Bottom-Up scenario, soft and hard gluons thermalize
at the same time. The time scale of thermal equilibration in BAMPS calculations
is of order \as^{-2} (\ln \as)^{-2} Q_s^{-1}. After this time the gluon
system exhibits nearly hydrodynamic behavior. The shear viscosity to entropy
density ratio has a weak dependence on and lies close to the lower bound
of the AdS/CFT conjecture.Comment: Quark Matter 2008 Proceeding
Relativistic Hartree approach including both positive- and negative-energy bound states
We develop a relativistic model to describe the bound states of positive
energy and negative energy in finite nuclei at the same time. Instead of
searching for the negative-energy solution of the nucleon's Dirac equation, we
solve the Dirac equations for the nucleon and the anti-nucleon simultaneously.
The single-particle energies of negative-energy nucleons are obtained through
changing the sign of the single-particle energies of positive-energy
anti-nucleons. The contributions of the Dirac sea to the source terms of the
meson fields are evaluated by means of the derivative expansion up to the
leading derivative order for the one-meson loop and one-nucleon loop. After
refitting the parameters of the model to the properties of spherical nuclei,
the results of positive-energy sector are similar to that calculated within the
commonly used relativistic mean field theory under the no-sea approximation.
However, the bound levels of negative-energy nucleons vary drastically when the
vacuum contributions are taken into account. It implies that the
negative-energy spectra deserve a sensitive probe to the effective interactions
in addition to the positive-energy spectra.Comment: 38 pages, Latex, 8 figures included; Int. J. Mod. Phys. E, in pres
Bound states of anti-nucleons in finite nuclei
We study the bound states of anti-nucleons emerging from the lower continuum
in finite nuclei within the relativistic Hartree approach including the
contributions of the Dirac sea to the source terms of the meson fields. The
Dirac equation is reduced to two Schr\"{o}dinger-equivalent equations for the
nucleon and the anti-nucleon respectively. These two equations are solved
simultaneously in an iteration procedure.
Numerical results show that the bound levels of anti-nucleons vary
drastically when the vacuum contributions are taken into account.Comment: 8 pages, no figures. Proceedings of International Conference on
Nonequilibrium and Nonlinear Dynamics in Nuclear and Other Finite Systems,
Beijing, China 2001; AIP conference proceedings 597, edited by Zhuxia Li, Ke
Wu, Xizhen Wu, Enguang Zhao, and F. Sakata (Melville, New York, 2001) page
112-11
Fast Dynamical Evolution of Hadron Resonance Gas via Hagedorn States
Hagedorn states are the key to understand how all hadrons observed in high
energy heavy ion collisions seem to reach thermal equilibrium so quickly. An
assembly of Hagedorn states is formed in elementary hadronic or heavy ion
collisions at hadronization. Microscopic simulations within the transport model
UrQMD allow to study the time evolution of such a pure non-equilibrated
Hagedorn state gas towards a thermally equilibrated Hadron Resonance Gas by
using dynamics, which unlike strings, fully respect detailed balance.
Propagation, repopulation, rescatterings and decays of Hagedorn states provide
the yields of all hadrons up to a mass of m=2.5 GeV. Ratios of feed down
corrected hadron multiplicities are compared to corresponding experimental data
from the ALICE collaboration at LHC. The quick thermalization within t=1-2 fm\c
of the emerging Hadron Resonance Gas exposes Hagedorn states as a tool to
understand hadronization.Comment: 5 pages, 7 figures, 1 tabl
Hadron production in relativistic nuclear collisions: thermal hadron source or hadronizing quark-gluon plasma?
Measured hadron yields from relativistic nuclear collisions can be equally
well understood in two physically distinct models, namely a static thermal
hadronic source vs.~a time-dependent, nonequilibrium hadronization off a
quark-gluon plasma droplet. Due to the time-dependent particle evaporation off
the hadronic surface in the latter approach the hadron ratios change (by
factors of ) in time. Final particle yields reflect time averages
over the actual thermodynamic properties of the system at a certain stage of
the evolution. Calculated hadron, strangelet and (anti-)cluster yields as well
as freeze-out times are presented for different systems. Due to strangeness
distillation the system moves rapidly out of the T, plane into the
-sector. Strangeness to baryon ratios f_s=1-2 prevail during a
considerable fraction (50%) of the time evolution (i.e. -droplets or
even -droplets form the system at the late stage: The possibility of
observing this time evolution via HBT correlations is discussed). The observed
hadron ratios require and . If
the present model is fit to the extrapolated hadron yields, metastable
hypermatter can only be produced with a probability for .Comment: Submitted to Z. Phys.
The Discovery of Quasisoft and Supersoft Sources in External Galaxies
We apply a uniform procedure to select very soft sources from point sources
observed by Chandra in 4 galaxies. This sample includes one elliptical galaxy
(NGC 4967), 2 face-on spirals (M101 and M83), and an interacting galaxy (M51).
We have found very soft X-ray sources (VSSs) in every galaxy. Some of these fit
the criteria for canonical supersoft sources (SSSs), while others are somewhat
harder. These latter have characteristic values of kT < 300 eV; we refer to
them as quasisoft sources (QSSs). We found a combined total of 149 VSSs in the
4 galaxies we considered; 77 were SSSs and 72 were QSSs. (See the paper for the
original long abstract)Comment: 20 pages, 6 figures. Accepted for publication in Ap
Properties of Dense Strange Hadronic Matter with Quark Degrees of Freedom
The properties of strange hadronic matter are studied in the context of the
modified quark-meson coupling model using two substantially different sets of
hyperon-hyperon () interactions. The first set is based on the Nijmegen
hard core potential model D with slightly attractive interactions. The
second potential set is based on the recent SU(3) extension of the Nijmegen
soft-core potential NSC97 with strongly attractive interactions which may
allow for deeply bound hypernuclear matter. The results show that, for the
first potential set, the hyperon does not appear at all in the bulk at
any baryon density and for all strangeness fractions. The binding energy curves
of the resulting system vary smoothly with density and the system
is stable (or metastable if we include the weak force). However, the situation
is drastically changed when using the second set where the hyperons
appear in the system at large baryon densities above a critical strangeness
fraction. We find strange hadronic matter undergoes a first order phase
transition from a system to a for strangeness
fractions and baryonic densities exceeding twice ordinary nuclear
matter density. Furthermore, it is found that the system built of
is deeply bound. This phase transition affects significantly the equation of
state which becomes much softer and a substantial drop in energy density and
pressure are detected as the phase transition takes place.Comment: 25 pages latex and 12 figures in postscript forma
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