323 research outputs found
Spin-orbit and tensor interactions in homogeneous matter of nucleons: accuracy of modern many-body theories
We study the energy per particle of symmetric nuclear matter and pure neutron
matter using realistic nucleon--nucleon potentials having non central tensor
and spin--orbit components, up to three times the empirical nuclear matter
saturation density, fm. The calculations are carried out
within the frameworks of the Brueckner--Bethe--Goldstone (BBG) and Correlated
Basis Functions (CBF) formalisms, in order to ascertain the accuracy of the
methods. The two hole--line approximation, with the continuous choice for the
single particle auxiliary potential, is adopted for the BBG approach, whereas
the variational Fermi Hypernetted Chain/Single Operator Chain theory, corrected
at the second order perturbative expansion level, is used in the CBF one. The
energies are then compared with the available Quantum and Variational Monte
Carlo results in neutron matter and with the BBG, up to the three hole--line
diagrams. For neutron matter and potentials without spin--orbit components all
methods, but perturbative CBF, are in reasonable agreement up to 3
. After the inclusion of the LS interactions, we still find agreement
around , whereas it is spoiled at larger densities. The spin--orbit
potential lowers the energy of neutron matter at by 3--4 MeV
per nucleon. In symmetric nuclear matter, the BBG and the variational results
are in agreement up to 1.5 . Beyond this density, and in
contrast with neutron matter, we find good agreement only for the potential
having spin--orbit components.Comment: 18 pages, 4 tables. Accepted in PL
Microscopic calculations of spin polarized neutron matter at finite temperature
The properties of spin polarized neutron matter are studied both at zero and
finite temperature within the framework of the Brueckner--Hartree--Fock
formalism, using the Argonne v18 nucleon-nucleon interaction. The free energy,
energy and entropy per particle are calculated for several values of the spin
polarization, densities and temperatures together with the magnetic
susceptibility of the system. The results show no indication of a ferromagnetic
transition at any density and temperature.Comment: 19 pages, 5 figure
Comparison of dynamical multifragmentation models
Multifragmentation scenarios, as predicted by antisymmetrized molecular
dynamics (AMD) or momentum-dependent stochastic mean-field (BGBD) calculations
are compared. While in the BGBD case fragment emission is clearly linked to the
spinodal decomposition mechanism, i.e. to mean-field instabilities, in AMD
many-body correlations have a stronger impact on the fragmentation dynamics and
clusters start to appear at earlier times. As a consequence, fragments are
formed on shorter time scales in AMD, on about equal footing of light particle
pre-equilibrium emission. Conversely, in BGBD pre-equilibrium and fragment
emissions happen on different time scales and are related to different
mechanisms
Microscopic calculation of neutrino mean free path inside hot neutron matter
We calculate the neutrino mean free path and the Equation of State of pure
neutron matter at finite temperature within a selfconsistent scheme based on
the Brueckner--Hartree--Fock approximation. We employ the nucleon-nucleon part
of the recent realistic baryon-baryon interaction (model NSC97e) constructed by
the Nijmegen group. The temperatures considered range from 10 to 80 MeV. We
report on the calculation of the mean field, the residual interaction and the
neutrino mean free path including short and long range correlations given by
the Brueckner--Hartree--Fock plus Random Phase Approximation (BHF+RPA)
framework. This is the first fully consistent calculation in hot neutron matter
dedicated to neutrino mean free path. We compare systematically our results to
those obtain with the D1P Gogny effective interaction, which is independent of
the temperature. The main differences between the present calculation and those
with nuclear effective interactions come from the RPA corrections to BHF (a
factor of about 8) while the temperature lack of consistency accounts for a
factor of about 2
Do strange stars exist in the Universe?
Definitely, an affirmative answer to this question would have implications of
fundamental importance for astrophysics (a new class of compact stars), and for
the physics of strong interactions (deconfined phase of quark matter, and
strange matter hypothesis). In the present work, we use observational data for
the newly discovered millisecond X-ray pulsar SAX J1808.4-3658 and for the
atoll source 4U 1728-34 to constrain the radius of the underlying compact
stars. Comparing the mass-radius relation of these two compact stars with
theoretical models for both neutron stars and strange stars, we argue that a
strange star model is more consistent with SAX J1808.4-3658 and 4U 1728-34, and
suggest that they are likely strange star candidates.Comment: In memory of Bhaskar Datta. -- Invited talk at the Pacific Rim
Conference on Stellar Astrophysics (Hong Kong, aug. 1999
Microscopic study of neutrino trapping in hyperon stars
Employing the most recent parametrization of the baryon-baryon interaction of
the Nijmegen group, we investigate, in the framework of the
Brueckner--Bethe--Goldstone many-body theory at zero temperature, the influence
of neutrino trapping on the composition, equation of state, and structure of
neutron stars, relevant to describe the physical conditions of a neutron star
immediately after birth (protoneutron star). We find that the presence of
neutrinos changes significantly the composition of matter delaying the
appearance of hyperons and making the equation of state stiffer. We explore the
consequences of neutrino trapping on the early evolution of a neutron star and
on the nature of the final compact remnant left by the supernova explosion.Comment: Astronomy & Astrophysics, 399, 687-693 (2003
Probing the isospin dependence of the in-medium nucleon-nucleon cross sections with radioactive beams
Within a transport model we search for potential probes of the isospin
dependence of the in-medium nucleon-nucleon (NN) cross sections. Traditional
measures of the nuclear stopping power are found sensitive to the magnitude but
they are ambiguous for determining the isospin dependence of the in-medium NN
cross sections. It is shown that isospin tracers, such as the neutron/proton
ratio of free nucleons, at backward rapidities/angles in nuclear reactions
induced by radioactive beams in inverse kinematics is a sensitive probe of the
isospin dependence of the in-medium NN cross sections. At forward
rapidities/angles, on the other hand, they are more sensitive to the density
dependence of the symmetry energy. Measurements of the rapidity/angular
dependence of the isospin transport in nuclear reactions will enable a better
understanding of the isospin dependence of in-medium nuclear effective
interactions.Comment: 19 pages including 7 figures, submitted to Phys. Rev.
Effect of symmetry energy on two-nucleon correlation functions in heavy-ion collisions induced by neutron-rich nuclei
Using an isospin-dependent transport model, we study the effects of nuclear
symmetry energy on two-nucleon correlation functions in heavy ion collisions
induced by neutron-rich nuclei. We find that the density dependence of the
nuclear symmetry energy affects significantly the nucleon emission times in
these collisions, leading to larger values of two-nucleon correlation functions
for a symmetry energy that has a stronger density dependence. Two-nucleon
correlation functions are thus useful tools for extracting information about
the nuclear symmetry energy from heavy ion collisions.Comment: Revised version, to appear in Phys. Rev. Let
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