17 research outputs found
Spin polarized neutron matter within the Dirac-Brueckner-Hartree-Fock approach
The relation between energy and density (known as the nuclear equation of
state) plays a major role in a variety of nuclear and astrophysical systems.
Spin and isospin asymmetries can have a dramatic impact on the equation of
state and possibly alter its stability conditions. An example is the possible
manifestation of ferromagnetic instabilities, which would indicate the
existence, at a certain density, of a spin-polarized state with lower energy
than the unpolarized one. This issue is being discussed extensively in the
literature and the conclusions are presently very model dependent. We will
report and discuss our recent progress in the study of spin-polarized neutron
matter. The approach we take is microscopic and relativistic. The calculated
neutron matter properties are derived from realistic nucleon-nucleon
interactions. This makes it possible to understand the nature of the EOS
properties in terms of specific features of the nuclear force model.Comment: 6 pages, 11 figures, revised/extended calculation
Multipair contributions to the spin response of nuclear matter
We analyse the effect of non-central forces on the magnetic susceptibility of
degenerate Fermi systems. These include the presence of contributions from
transitions to states containing more than one quasiparticle-quasihole pair,
which cannot be calculated within the framework of Landau Fermi-liquid theory,
and renormalization of the quasiparticle magnetic moment, as well as explicit
non-central contributions to the quasiparticle interaction. Consequently, the
relationship between the Landau parameters and the magnetic susceptibility for
Fermi systems with non-central forces is considerably more complicated than for
systems with central forces. We use sum-rule arguments to place a lower bound
on the contribution to the static susceptibility coming from transitions to
multipair states
Competition of ferromagnetic and antiferromagnetic spin ordering in nuclear matter
In the framework of a Fermi liquid theory it is considered the possibility of
ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear
matter with Skyrme effective interaction. The zero temperature dependence of
ferromagnetic and antiferromagnetic spin polarization parameters as functions
of density is found for SkM, SGII effective forces. It is shown that in the
density domain, where both type of solutions of self--consistent equations
exist, ferromagnetic spin state is more preferable than antiferromagnetic one.Comment: 9p., 3 figure
Equation of state and magnetic susceptibility of spin polarized isospin asymmetric nuclear matter
Properties of spin polarized isospin asymmetric nuclear matter are studied
within the framework of the Brueckner--Hartree--Fock formalism. The
single-particle potentials of neutrons and protons with spin up and down are
determined for several values of the neutron and proton spin polarizations and
the asymmetry parameter. It is found an almost linear and symmetric variation
of the single-particle potentials as increasing these parameters. An analytic
parametrization of the total energy per particle as a function of the asymmetry
and spin polarizations is constructed. This parametrization is employed to
compute the magnetic susceptibility of nuclear matter for several values of the
asymmetry from neutron to symmetric matter. The results show no indication of a
ferromagnetic transition at any density for any asymmetry of nuclear matter.Comment: 23 pages, 8 figures, 2 tables (submitted to Phys. Rev. C
Phase transition to the state with nonzero average helicity in dense neutron matter
The possibility of the appearance of the states with a nonzero average
helicity in neutron matter is studied in the model with the Skyrme effective
interaction. By providing the analysis of the self-consistent equations at zero
temperature, it is shown that neutron matter with the Skyrme BSk18 effective
force undergoes at high densities a phase transition to the state in which the
degeneracy with respect to helicity of neutrons is spontaneously removed.Comment: 4 pages, 3 figures; v2: journal versio
Pairing in nuclear systems: from neutron stars to finite nuclei
We discuss several pairing-related phenomena in nuclear systems, ranging from
superfluidity in neutron stars to the gradual breaking of pairs in finite
nuclei. We focus on the links between many-body pairing as it evolves from the
underlying nucleon-nucleon interaction and the eventual experimental and
theoretical manifestations of superfluidity in infinite nuclear matter and of
pairing in finite nuclei. We analyse the nature of pair correlations in nuclei
and their potential impact on nuclear structure experiments. We also describe
recent experimental evidence that points to a relation between pairing and
phase transitions (or transformations) in finite nuclear systems. Finally, we
discuss recent investigations of ground-state properties of random two-body
interactions where pairing plays little role although the interactions yield
interesting nuclear properties such as 0+ ground states in even-even nuclei.Comment: 74 pages, 33 figs, uses revtex4. Submitted to Reviews of Modern
Physic
Pairing with polarization effects in low-density neutron matter
We study the properties of the 1S0 pairing gap in low-density neutron matter. Different corrections to the lowest-order scattering length approximation are explored, resulting in a strong suppression with respect to the BCS result