3,237 research outputs found
A realistic model of superfluidity in the neutron star inner crust
A semi-microscopic self-consistent quantum approach developed recently to
describe the inner crust structure of neutron stars within the Wigner-Seitz
(WS) method with the explicit inclusion of neutron and proton pairing
correlations is further developed. In this approach, the generalized energy
functional is used which contains the anomalous term describing the pairing. It
is constructed by matching the realistic phenomenological functional by Fayans
et al. for describing the nuclear-type cluster in the center of the WS cell
with the one calculated microscopically for neutron matter. Previously the
anomalous part of the latter was calculated within the BCS approximation. In
this work corrections to the BCS theory which are known from the many-body
theory of pairing in neutron matter are included into the energy functional in
an approximate way. These modifications have a sizable influence on the
equilibrium configuration of the inner crust, i.e. on the proton charge Z and
the radius R_c of the WS cell. The effects are quite significant in the region
where the neutron pairing gap is larger.Comment: 24 pages, 14 figures; LaTeX, submitted to EPJ
Neutron matter at low density and the unitary limit
Neutron matter at low density is studied within the hole-line expansion.
Calculations are performed in the range of Fermi momentum between 0.4 and
0.8 fm. It is found that the Equation of State is determined by the
channel only, the three-body forces contribution is quite small, the
effect of the single particle potential is negligible and the three hole-line
contribution is below 5% of the total energy and indeed vanishing small at the
lowest densities. Despite the unitary limit is actually never reached, the
total energy stays very close to one half of the free gas value throughout the
considered density range. A rank one separable representation of the bare NN
interaction, which reproduces the physical scattering length and effective
range, gives results almost indistinguishable from the full Brueckner G-matrix
calculations with a realistic force. The extension of the calculations below
fm does not indicate any pathological behavior of the
neutron Equation of State.Comment: 17 pages, 7 figures. To be published in Phys. Rev.
Structure of hybrid protoneutron stars within the Nambu--Jona-Lasinio model
We investigate the structure of protoneutron stars (PNS) formed by hadronic
and quark matter in -equilibrium described by appropriate equations of
state (EOS). For the hadronic matter, we use a finite temperature EOS based on
the Brueckner-Bethe-Goldstone many-body theory, with realistic two- and
three-body forces. For the quark sector, we employ the Nambu--Jona-Lasinio
model. We find that the maximum allowed masses are comprised in a narrow range
around 1.8 solar masses, with a slight dependence on the temperature.
Metastable hybrid protoneutron stars are not found.Comment: 7 pages, 6 figures, revised version accepted for publication in Phys.
Rev.
In-medium enhancement of the modified Urca neutrino reaction rates
We calculate modified Urca neutrino emission rates in the dense nuclear
matter in neutron star cores. We find that these rates are strongly enhanced in
the beta-stable matter in regions of the core close to the direct Urca process
threshold. This enhancement can be tracked to the use of the in-medium nucleon
spectrum in the virtual nucleon propagator. We describe the in-medium nucleon
scattering in the non-relativistic Bruckner-Hartree-Fock framework taking into
account two-body as well as the effective three-body forces, although the
proposed enhancement does not rely on a particular way of the nucleon
interaction treatment. Finally we suggest a simple approximate expression for
the emissivity of the n-branch of the modified Urca process that can be used in
the neutron stars cooling simulations with any nucleon equation of state of
dense matter.Comment: 8 pages, 3 figures; accepted for publication in PLB. In v.2 misprint
in eq.(9) corrected and discussion of cooling curves expande
Spin-orbit correlation energy in neutron matter
We study the relevance of the energy correlation produced by the two-body
spin-orbit coupling present in realistic nucleon-nucleon potentials. To this
purpose, the neutron matter Equation of State (EoS) is calculated with the
realistic two-body Argonne potential. The shift occuring in the EoS when
spin-orbit terms are removed is taken as an estimate of the spin-orbit
correlation energy. Results obtained within the Bethe-Brueckner-Goldstone
expansion, extended up to three hole-line diagrams, are compared with other
many-body calculations recently presented in the literature. In particular,
excellent agreement is found with the Green's function Monte-Carlo method. This
agreement indicates the present theoretical accuracy in the calculation of the
neutron matter EoS.Comment: 5 pages, 2 figures, 2 tables; to appear in Phys. Rev.
An ab initio theory of double odd-even mass differences in nuclei
Two aspects of the problem of evaluating double odd-even mass differences D_2
in semi-magic nuclei are studied related to existence of two components with
different properties, a superfluid nuclear subsystem and a non-superfluid one.
For the superfluid subsystem, the difference D_2 is approximately equal to
2\Delta, the gap \Delta being the solution of the gap equation. For the
non-superfluid subsystem, D_2 is found by solving the equation for two-particle
Green function for normal systems. Both equations under consideration contain
the same effective pairing interaction. For the latter, the semi-microscopic
model is used in which the main term calculated from the first principles is
supplemented with a small phenomenological addendum containing one
phenomenological parameter supposed to be universal for all medium and heavy
atomic nuclei.Comment: 7 pages, 10 figures, Report at Nuclear Structure and Related Topics,
Dubna, Russia, July 2 - July 7, 201
Hybrid protoneutron stars with the MIT bag model
We study the hadron-quark phase transition in the interior of protoneutron
stars. For the hadronic sector, we use a microscopic equation of state
involving nucleons and hyperons derived within the finite-temperature
Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and
three-body forces. For the description of quark matter, we employ the MIT bag
model both with a constant and a density-dependent bag parameter. We calculate
the structure of protostars with the equation of state comprising both phases
and find maximum masses below 1.6 solar masses. Metastable heavy hybrid
protostars are not found.Comment: 12 pages, 9 figures submitted to Phys. Rev.
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