249 research outputs found
Nuclear matter and neutron matter for improved quark mass density- dependent model with mesons
A new improved quark mass density-dependent model including u, d quarks,
mesons, mesons and mesons is presented. Employing this
model, the properties of nuclear matter, neutron matter and neutron star are
studied. We find that it can describe above properties successfully. The
results given by the new improved quark mass density- dependent model and by
the quark meson coupling model are compared.Comment: 18 pages, 7 figure
Effective hadron masses and couplings in nuclear matter and incompressibility
The role of effective hadron masses and effective couplings in nuclear matter
is studied using a generalized effective Lagrangian for sigma-omega model. A
simple relation among the effective masses, the effective couplings and the
incompressibility K is derived. Using the relation, it is found that the
effective repulsive and the effective attractive forces are almost canceled to
each other at the normal density. Inversely, if this cancellation is almost
complete, K should be 250-350MeV.Comment: 13 pages of text, 16 figure
Finite Nuclei in a Relativistic Mean-Field Model with Derivative Couplings
We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski
model and one of its variations (the ZM3 model). We calculate energy levels and
ground-state properties in nuclei where the mean-field approach is reliable.
The role played by the spin-orbit potential in sorting out mean-field model
descriptions is emphasized.Comment: 17 pages, 9 figures, 30 kbytes. Uses EPSF.TEX. To appear in Zeit. f.
Phys. A (Hadrons and Nuclei
Hadrons in Dense Resonance-Matter: A Chiral SU(3) Approach
A nonlinear chiral SU(3) approach including the spin 3/2 decuplet is
developed to describe dense matter. The coupling constants of the baryon
resonances to the scalar mesons are determined from the decuplet vacuum masses
and SU(3) symmetry relations. Different methods of mass generation show
significant differences in the properties of the spin-3/2 particles and in the
nuclear equation of state.Comment: 28 pages, 9 figure
Probing the equation of state in the AGS energy range with 3-d hydrodynamics
The effect of (i) the phase transition between a quark gluon plasma (QGP) and
a hadron gas and (ii) the number of resonance degrees of freedom in the
hadronic phase on the single inclusive distributions of 16 different types of
produced hadrons for Au+Au collisions at AGS energies is studied.
We have used an exact numerical solution of the relativistic hydrodynamical
equations without free parameters which, because of its 3-d character,
constitutes a considerable improvement over the classical Landau solution.
Using two different equations of state (eos) - one containing a phase
transition from QGP to the Hadronic Phase and two versions of a purely hadronic
eos - we find that the first one gives an overall better description of the
Au+Au experimental data at energies.
We reproduce and analyse measured meson and proton spectra and also make
predictions for anti-protons, deltas, anti-deltas and hyperons. The low m_t
enhancement in pi- spectra is explained by baryon number conservation and
strangeness equilibration.
We also find that negative kaon data are more sensitive to the eos, as well
as the K-/pi- ratio. All hyperons and deltas are sensitive to the presence of a
phase transition in the forward rapidity region. Anti-protons, Omegas and heavy
anti-baryons are sensitive in the whole rapidity range.Comment: 25 pages (.tex) and 9 figures (.ps
Derivative-Coupling Models and the Nuclear-Matter Equation of State
The equation of state of saturated nuclear matter is derived using two
different derivative-coupling Lagrangians. We show that both descriptions are
equivalent and can be obtained from the sigma-omega model through an
appropriate rescaling of the coupling constants. We introduce generalized forms
of this rescaling to study the correlations amongst observables in infinite
nuclear matter, in particular, the compressibility and the effective nucleon
mass.Comment: 16 pages, 6 figures, 36 kbytes. To appear in Zeit. f. Phys. A
(Hadrons and Nuclei
Structure of the Vacuum in Nuclear Matter - A Nonperturbative Approach
We compute the vacuum polarisation correction to the binding energy of
nuclear matter in the Walecka model using a nonperturbative approach. We first
study such a contribution as arising from a ground state structure with
baryon-antibaryon condensates. This yields the same results as obtained through
the relativistic Hartree approximation of summing tadpole diagrams for the
baryon propagator. Such a vacuum is then generalized to include quantum effects
from meson fields through scalar-meson condensates. The method is applied to
study properties of nuclear matter and leads to a softer equation of state
giving a lower value of the incompressibility than would be reached without
quantum effects. The density dependent effective sigma mass is also calculated
including such vacuum polarisation effects.Comment: 26 pages including 5 eps files, uses revtex style; PACS number:
21.65.+f,21.30.+
Anatomy of a microearthquake sequence on an active normal fault
The analysis of similar earthquakes, such as events in a seismic sequence, is an effective tool with which to monitor and study source processes and to understand the mechanical and dynamic states of active fault systems. We are observing seismicity that is primarily concentrated in very limited regions along the 1980 Irpinia earthquake fault zone in Southern Italy, which is a complex system characterised by extensional stress regime. These zones of weakness produce repeated earthquakes and swarm-like microearthquake sequences, which are concentrated in a few specific zones of the fault system. In this study, we focused on a sequence that occurred along the main fault segment of the 1980 Irpinia earthquake to understand its characteristics and its relation to the loading-unloading mechanisms of the fault system
Hydrodynamical analysis of symmetric nucleus-nucleus collisions at CERN/SPS energies
We present a coherent theoretical study of ultrarelativistic heavy-ion data
obtained at the CERN/SPS by the NA35/NA49 Collaborations using 3+1-dimensional
relativistic hydrodynamics. We find excellent agreement with the rapidity
spectra of negative hadrons and protons and with the correlation measurements
in two experiments: at 200 and at 160 (preliminary
results). Within our model this implies that for () a
quark-gluon-plasma of initial volume 174 (24 ) with a lifetime 3.4
(1.5 ) was formed. It is found that the Bose-Einstein correlation
measurements do not determine the maximal effective radii of the hadron sources
because of the large contributions from resonance decay at small momenta. Also
within this study we present an NA49 acceptance corrected two-pion
Bose-Einstein correlation function in the invariant variable, .Comment: 21 pages, 11 Postscript figures (1 File, 775654 Bytes, has to be
requested for submission via e.mail from [email protected]
Phase Transitions in Warm, Asymmetric Nuclear Matter
A relativistic mean-field model of nuclear matter with arbitrary proton
fraction is studied at finite temperature. An analysis is performed of the
liquid-gas phase transition in a system with two conserved charges (baryon
number and isospin) using the stability conditions on the free energy, the
conservation laws, and Gibbs' criteria for phase equilibrium. For a binary
system with two phases, the coexistence surface (binodal) is two-dimensional.
The Maxwell construction through the phase-separation region is discussed, and
it is shown that the stable configuration can be determined uniquely at every
density. Moreover, because of the greater dimensionality of the binodal
surface, the liquid-gas phase transition is continuous (second order by
Ehrenfest's definition), rather than discontinuous (first order), as in
familiar one-component systems. Using a mean-field equation of state calibrated
to the properties of nuclear matter and finite nuclei, various phase-separation
scenarios are considered. The model is then applied to the liquid-gas phase
transition that may occur in the warm, dilute matter produced in energetic
heavy-ion collisions. In asymmetric matter, instabilities that produce a
liquid-gas phase separation arise from fluctuations in the proton concentration
(chemical instability), rather than from fluctuations in the baryon density
(mechanical instability).Comment: Postscript file, 50 pages including 23 figure
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