52,792 research outputs found
VISHNU hybrid model for viscous QCD matter at RHIC and LHC energies
In this proceeding, we briefly describe the viscous hydrodynamics + hadron
cascade hybrid model VISHNU for relativistic heavy ion collisions and report
the current status on extracting the QGP viscosity from elliptic flow data.Comment: 4 pages, 1 figure, the proceedings of 7th International Workshop on
Critical Point and Onset of Deconfinement, Wuhan, China, Nov. 7-11, 201
Warm Asymmetric Nuclear Matter and Proto-Neutron Star
Asymmetric nuclear matter equation of state at finite temperature is studied
in SU(2) chiral sigma model using mean field approximation. The effect of
temperature on effective mass, entropy, and binding energy is discussed.
Treating the system as one with two conserved charges the liquid-gas phase
transition is investigated. We have also discussed the effect of proton
fraction on critical temperature with and without -meson contribution. We
have extended our work to study the structure of proto-neutron star with
neutron free charge-neutral matter in beta-equilibrium. We found that the mass
and radius of the star decreases as it cools from the entropy per baryon S = 2
to S = 0 and the maximum temperature of the core of the star is about 62 MeV
for S = 2.Comment: 25 pages, 16 figure
Massive star evolution in close binaries:conditions for homogeneous chemical evolution
We investigate the impact of tidal interactions, before any mass transfer, on
various properties of the stellar models. We study the conditions for obtaining
homogeneous evolution triggered by tidal interactions, and for avoiding any
Roche lobe overflow during the Main-Sequence phase. We consider the case of
rotating stars computed with a strong coupling mediated by an interior magnetic
field. In models without any tidal interaction (single stars and wide
binaries), homogeneous evolution in solid body rotating models is obtained when
two conditions are realized: the initial rotation must be high enough, the loss
of angular momentum by stellar winds should be modest. This last point favors
metal-poor fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is high enough
(typically a time-averaged surface velocities during the Main-Sequence phase
above 250 km s), whatever the mass losses. In close binaries, mixing is
stronger at higher than at lower metallicities. Homogeneous evolution is thus
favored at higher metallicities. Roche lobe overflow avoidance is favored at
lower metallicities due to the fact that stars with less metals remain more
compact. We study also the impact of different processes for the angular
momentum transport on the surface abundances and velocities in single and close
binaries. In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in binary or
single star models. In contrast, models computed with mild coupling may produce
strong surface enrichments associated to low surface velocities. Close binary
models may be of interest for explaining homogeneous massive stars, fast
rotating Wolf-Rayet stars, and progenitors of long soft gamma ray bursts, even
at high metallicities.Comment: 21 pages, 13 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Determining SUSY Parameters in Chargino Pair-Production in Collisions
In most supersymmetric theories, charginos , mixtures
of charged color-neutral gauginos and higgsinos, belong to the class of the
lightest supersymmetric particles. They are easy to observe at
colliders. By measuring the total cross sections and the left-right asymmetries
with polarized electron beams in , the chargino masses and the gaugino-higgsino mixing angles can be
determined. From these observables the fundamental SUSY parameters can be
derived: the SU(2) gaugino mass , the modulus and
of the higgsino mass parameter, and , the ratio of the
vacuum expectation values of the two neutral Higgs doublet fields. The
solutions are unique; the CP-violating phase can be determined
uniquely by analyzing effects due to the normal polarization of the charginos.Comment: 20 pages, 4 figures, uses axodraw.st
Experimental measurement of an effective temperature for jammed granular materials
A densely packed granular system is an example of an out-of-equilibrium
system in the jammed state. It has been a longstanding problem to determine
whether this class of systems can be described by concepts arising from
equilibrium statistical mechanics, such as an ``effective temperature'' and
``compactivity''. The measurement of the effective temperature is realized in
the laboratory by slowly shearing a closely-packed ensemble of spherical beads
confined by an external pressure in a Couette geometry. All the probe particles
considered in this study, independent of their characteristic features,
equilibrate at the same temperature, given by the packing density of the
system.Comment: 22 pages, 7 figures, more informations at http://www.jamlab.or
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