58 research outputs found
Spinodal instabilities within BUU approach
Using a recently developed method for the inclusion of fluctuation in the BUU
dynamics, we study the self-consistent propagation of inherent thermal noise of
unstable nuclear matter. The large time behaviour of the evolving system
exhibits synergism between fluctuation and non-linearities in a universal
manner which manifest in the appearance of macroscopic structure in the average
description.Comment: 12 pages Revtex. Two figures, uuencoded, are enclosed in a separate
fil
Chaos vs. Linear Instability in the Vlasov Equation: A Fractal Analysis Characterization
In this work we discuss the most recent results concerning the Vlasov
dynamics inside the spinodal region. The chaotic behaviour which follows an
initial regular evolution is characterized through the calculation of the
fractal dimension of the distribution of the final modes excited. The ambiguous
role of the largest Lyapunov exponent for unstable systems is also critically
reviewed.Comment: 10 pages, RevTeX, 4 figures not included but available upon reques
Giant Octupole Resonance Simulation
Using a pseudo-particle technique we simulate large-amplitude isoscalar giant
octupole excitations in a finite nuclear system. Dependent on the initial
conditions we observe either clear octupole modes or over-damped octupole modes
which decay immediately into quadrupole ones. This shows clearly a behavior
beyond linear response. We propose that octupole modes might be observed in
central collisions of heavy ions
Non-Linear Mean Field Dynamics in the Nuclear Spinodal Zone
We demonstrate, by numerical simulations, that the dynamics of nuclear matter
mean field inside the spinodal region is chaotic. Spontaneous symmetry-breaking
- no explicit fluctuating term is considered - occurs leading to wild
unpredictable density fluctuations. A proper recipe to calculate an average
Lyapunov exponent in this multidimensional phase space is introduced. The
latter is calculated for different values of the density in order to
characterize in a quantitative way the chaotic and regular regions. It is
argued that the mean field chaoticity can be the main mechanism of the nuclear
multifragmentation occurring in the intermediate energy reactions.Comment: 11 pages (3 figures not included but available upon request). In
RevTex (version 3.0). Catania University preprint no.93/2
Neutron stars and the transition to color-superconducting quark matter
We explore the relevance of color superconductivity inside a possible quark
matter core for the bulk properties of neutron stars. For the quark phase we
use an Nambu--Jona-Lasinio (NJL) type model, extended to include diquark
condensates. For the hadronic phase, a microscopic many-body model is adopted,
with and without strangeness content. In our calculations, a sharp boundary is
assumed between the hadronic and the quark phases. For NJL model parameters
fitted to vacuum properties we find that no star with a pure quark core does
exist. Nevertheless the presence of color superconducting phases can lower the
neutron star maximum mass substantially. In some cases, the transition to quark
matter occurs only if color superconductivity is present. Once the quark phase
is introduced, the value of the maximum mass stays in any case below the value
of two solar masses.Comment: 11 pages, 3 figures, v2: minor corrections in the text, layout of the
figures improved, references added, v3: transition densities from hadronic to
quark matter added, version accepted for publication in PL
Hybrid stars with the color dielectric and the MIT bag models
We study the hadron-quark phase transition in the interior of neutron stars
(NS). For the hadronic sector, we use a microscopic equation of state (EOS)
involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone
many-body theory, with realistic two-body and three-body forces. For the
description of quark matter, we employ both the MIT bag model with a density
dependent bag constant, and the color dielectric model. We calculate the
structure of NS interiors with the EOS comprising both phases, and we find that
the NS maximum masses are never larger than 1.7 solar masses, no matter the
model chosen for describing the pure quark phase.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Strange stars in Krori-Barua space-time
The singularity space-time metric obtained by Krori and Barua\cite{Krori1975}
satisfies the physical requirements of a realistic star. Consequently, we
explore the possibility of applying the Krori and Barua model to describe
ultra-compact objects like strange stars. For it to become a viable model for
strange stars, bounds on the model parameters have been obtained. Consequences
of a mathematical description to model strange stars have been analyzed.Comment: 9 pages (two column), 12 figures. Some changes have been made. " To
appear in European Physical Journal C
The hadron-quark phase transition in dense matter and neutron stars
We study the hadron-quark phase transition in the interior of neutron stars
(NS's). We calculate the equation of state (EOS) of hadronic matter using the
Brueckner-Bethe-Goldstone formalism with realistic two-body and three-body
forces, as well as a relativistic mean field model. For quark matter we employ
the MIT bag model constraining the bag constant by using the indications coming
from the recent experimental results obtained at the CERN SPS on the formation
of a quark-gluon plasma. We find necessary to introduce a density dependent bag
parameter, and the corresponding consistent thermodynamical formalism. We
calculate the structure of NS interiors with the EOS comprising both phases,
and we find that the NS maximum masses fall in a relatively narrow interval,
. The precise value of the
maximum mass turns out to be only weakly correlated with the value of the
energy density at the assumed transition point in nearly symmetric nuclear
matter.Comment: 25 pages, Revtex4, 16 figures included as postscrip
Strange Stars with a Density-Dependent Bag Parameter
We have studied strange quark stars in the framework of the MIT bag model,
allowing the bag parameter B to depend on the density of the medium. We have
also studied the effect of Cooper pairing among quarks, on the stellar
structure. Comparison of these two effects shows that the former is generally
more significant. We studied the resulting equation of state of the quark
matter, stellar mass-radius relation, mass-central-density relation,
radius-central-density relation, and the variation of the density as a function
of the distance from the centre of the star. We found that the
density-dependent B allows stars with larger masses and radii, due to
stiffening of the equation of state. Interestingly, certain stellar
configurations are found to be possible only if B depends on the density. We
have also studied the effect of variation of the superconducting gap parameter
on our results.Comment: 23 pages, 8 figs; v2: 25 pages, 9 figs, version to be published in
Phys. Rev. (D
- …