140 research outputs found
Neutron matter under strong magnetic fields: a comparison of models
The equation of state of neutron matter is affected by the presence of a
magnetic field due to the intrinsic magnetic moment of the neutron. Here we
study the equilibrium configuration of this system for a wide range of
densities, temperatures and magnetic fields. Special attention is paid to the
behavior of the isothermal compressibility and the magnetic susceptibility. Our
calculation is performed using both microscopic and phenomenological approaches
of the neutron matter equation of state, namely the Brueckner--Hartree--Fock
(BHF) approach using the Argonne V18 nucleon-nucleon potential supplemented
with the Urbana IX three-nucleon force, the effective Skyrme model in a
Hartree--Fock description, and the Quantum Hadrodynamic formulation with a mean
field approximation. All these approaches predict a change from completely spin
polarized to partially polarized matter that leads to a continuous equation of
state. The compressibility and the magnetic susceptibility show characteristic
behaviors, which reflect that fact. Thermal effects tend to smear out the
sharpness found for these quantities at T=0. In most cases a thermal increase
of 10 MeV is enough to hide the signals of the change of polarization. The set
of densities and magnetic field intensities for which the system changes it
spin polarization is different for each model. However, there is an overall
agreement between the three theoretical descriptions.Comment: updated to correspond with the published versio
Spin polarized neutron matte and magnetic susceptibility within the Brueckner-Hartree-Fock approximation
The Brueckner--Hartree--Fock formalism is applied to study spin polarized
neutron matter properties. Results of the total energy per particle as a
function of the spin polarization and density are presented for two modern
realistic nucleon-nucleon interactions, Nijmegen II and Reid93. We find that
the dependence of the energy on the spin polarization is practically parabolic
in the full range of polarizations. The magnetic susceptibility of the system
is computed. Our results show no indication of a ferromagnetic transition which
becomes even more difficult as the density increases.Comment: 15 pages, 4 figures (Submitted to PRC
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
Hyperon effects on the properties of -stable neutron star matter
We present results from Brueckner-Hartree-Fock calculations for
-stable neutron star matter with nucleonic and hyperonic degrees of
freedom employing the most recent parametrizations of the baryon-baryon
interaction of the Nijmegen group. Only and are present up
to densities . The corresponding equations of state are then used
to compute properties of neutron stars such as masses and radii.Comment: 4 pages, contributed talk at HYP2000, Torino, 23-27 Oct. 200
Constraining the nuclear equation of state at subsaturation densities
Only one third of the nucleons in Pb occupy the saturation density
area. Consequently nuclear observables related to average properties of nuclei,
such as masses or radii, constrain the equation of state (EOS) not at
saturation density but rather around the so-called crossing density, localised
close to the mean value of the density of nuclei: 0.11 fm.
This provides an explanation for the empirical fact that several EOS quantities
calculated with various functionals cross at a density significantly lower than
the saturation one. The third derivative M of the energy at the crossing
density is constrained by the giant monopole resonance (GMR) measurements in an
isotopic chain rather than the incompressibility at saturation density. The GMR
measurements provide M=1110 70 MeV (6% uncertainty), whose extrapolation
gives K=230 40 MeV (17% uncertainty).Comment: 4 pages, 4 figure
Landau parameters of nuclear matter in the spin and spin-isospin channels
The equation of state of spin and isospin polarized nuclear matter is
determined in the framework of the Brueckner theory including three-body
forces. The Landau parameters in the spin and spin-isospin sectors are derived
as a function of the baryonic density. The results are compared with the
Gamow-Teller collective modes. The relevance of and for neutron
stars is shortly discussed, including the magnetic susceptibility and the
neutron star cooling.Comment: 2 pages, 2 figures, RevTex4 forma
Open charm meson in nuclear matter at finite temperature beyond the zero range approximation
The properties of open charm mesons, , , and in
nuclear matter at finite temperature are studied within a self-consistent
coupled-channel approach. The interaction of the low lying pseudoscalar mesons
with the ground state baryons in the charm sector is derived from a -channel
vector-exchange model. The in-medium scattering amplitudes are obtained by
solving the Lippmann-Schwinger equation at finite temperature including Pauli
blocking effects, as well as , , and self-energies
taking their mutual influence into account. We find that the in-medium
properties of the meson are affected by the -meson self-energy through
the intermediate loops coupled to states. Similarly, dressing the
meson in the loops has an influence over the properties of
the meson.Comment: 23 pages, 9 figures, 2 table
Dynamically generated open charmed baryons beyond the zero range approximation
The interaction of the low lying pseudo-scalar mesons with the ground state
baryons in the charm sector is studied within a coupled channel approach using
a t-channel vector-exchange driving force. The amplitudes describing the
scattering of the pseudo-scalar mesons off the ground-state baryons are
obtained by solving the Lippmann--Schwinger equation. We analyze in detail the
effects of going beyond the approximation. Our model predicts the
dynamical generation of several open charmed baryon resonances in different
isospin and strangeness channels, some of which can be clearly identified with
recently observed states.Comment: 7 figures, 8 table
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