410 research outputs found
Mean Field Calculation of Thermal Properties of Simple Nucleon Matter on a Lattice
Thermal properties of single species nucleon matter are investigated assuming
a simple form of the nucleon-nucleon interaction. The nucleons are placed on a
cubic lattice, hopping from site to site and interacting through a
spin-dependent force, as in the extended, attractive Hubbard model. A mean
field calculation in the Hartree-Fock Bogoliubov approximation suggests that
the superfluid ground state generated by strong nucleon pairing undergoes a
second-order phase transition to a normal state as the temperature increases.
The calculation is shown to lead to a promising description of the thermal
properties of low-density neutron matter. A possibility of a density wave phase
is also examined.Comment: 30 pages, 8 figures, to appear in Physical Review
Possibility of \Lambda\Lambda pairing and its dependence on background density in relativistic Hartree-Bogoliubov model
We calculate a \Lambda\Lambda pairing gap in binary mixed matter of nucleons
and \Lambda hyperons within the relativistic Hartree-Bogoliubov model. Lambda
hyperons to be paired up are immersed in background nucleons in a normal state.
The gap is calculated with a one-boson-exchange interaction obtained from a
relativistic Lagrangian. It is found that at background density
\rho_{N}=2.5\rho_{0} the \Lambda\Lambda pairing gap is very small, and that
denser background makes it rapidly suppressed. This result suggests a
mechanism, specific to mixed matter dealt with relativistic models, of its
dependence on the nucleon density. An effect of weaker \Lambda\Lambda
attraction on the gap is also examined in connection with revised information
of the \Lambda\Lambda interaction.Comment: 8 pages, 6 figures, REVTeX 4; substantially rewritten, emphasis is
put on the LL pairing in pure neutron matte
Superfluidity of hyperons in -stable neutron star matter
In this work we evaluate the energy gap of hyperons in
-stable neutron star matter. We solve the BCS gap equation for an
effective pairing interaction derived from the most recent
parametrization of the hyperon-hyperon interaction constructed by the Nijmegen
group. We find that the hyperons are in a superfluid state
in the density region fm, with a maximum energy gap of
order 8 MeV at a total baryon number density of fm and a
fraction of about 8%. We examine the implications on neutron star
cooling.Comment: 4 pages, double column, 4 figures. Accepted in PR
Extended-soft-core Baryon-Baryon Model II. Hyperon-Nucleon Interaction
The YN results are presented from the Extended-soft-core (ESC) interactions.
They consist of local- and non-local-potentials due to (i) One-boson-exchange
(OBE), with pseudoscalar-, vector-, scalar-, and axial-vector-nonets, (ii)
Diffractive exchanges, (iii) Two-pseudoscalar exchange, and (iv)
Meson-pair-exchange (MPE). This model, called ESC04, describes NN and YN in a
unified way using broken flavor SU(3)-symmetry. Novel ingredients are the
inclusion of (i) the axial-vector-mesons, (ii) a zero in the scalar- and
axial-vector meson form factors. We describe simultaneous fits to the NN- and
YN-data, using four options in the ESC-model. Very good fits were obtained.
G-matrix calculations with these four options are also reported. The obtained
well depths (U_\Lambda, U_\Sigma, U_\Xi) reveal distinct features of ESC04a-d.
The \Lambda\Lambda-interactions are demonstrated to be consistent with the
observed data of_{\Lambda\Lambda}^6He. The possible three-body effects are
investigated by considering phenomenologically the changes of the vector-meson
masses in a nuclear medium.Comment: preprint vesion 66 pages, two-column version 27 pages, 17 figure
Superfluid Phase Transitions in Dense Neutron Matter
The phase transitions in a realistic system with triplet pairing, dense
neutron matter, have been investigated. The spectrum of phases of the
model, which adequately describes pairing in this system, is
analytically constructed with the aid of a separation method for solving BCS
gap equation in states of arbitrary angular momentum. In addition to solutions
involving a single value of the magnetic quantum number (and its negative),
there exist ten real multicomponent solutions. Five of the corresponding
angle-dependent order parameters have nodes, and five do not. In contrast to
the case of superfluid He, transitions occur between phases with nodeless
order parameters. The temperature dependence of the competition between the
various phases is studied.Comment: 11 pages, 2 figure
Quark description of the Nambu-Goldstone bosons in the color-flavor locked phase
We investigate the color-singlet order parameters and the quark description
of the Nambu-Goldstone (NG) bosons in the color-flavor locked (CFL) phase. We
put emphasis on the NG boson (phason) called ``H'' associated with the
symmetry breaking. We qualitatively argue the nature of H as
the second sound in the hydrodynamic regime. We articulate, based on a diquark
picture, how the structural change of the condensates and the associated NG
bosons occurs continuously from hadronic to CFL quark matter if the
quark-hadron continuity is realized. We sharpen the qualitative difference
between the flavor octet pions and the singlet phason. We propose a conjecture
that superfluid H matter undergoes a crossover to a superconductor with
tightly-bound diquarks, and then a crossover to superconducting matter with
diquarks dissociated.Comment: 14 pages, 1 table, 1 figure and confusing statements are correcte
S-wave Pairing of Hyperons in Dense Matter
In this work we calculate the gap energies of hyperons in
neutron star matter. The calculation is based on a solution of the BCS gap
equation for an effective G-matrix parameterization of the
interaction with a nuclear matter background, presented recently by Lanskoy and
Yamamoto. We find that a gap energy of a few tenths of MeV is expected for
Fermi momenta up to about 1.3 fm. Implications for neutron
star matter are examined, and suggest the existence of a
superfluid between the threshold baryon density for formation and the
baryon density where the fraction reaches .Comment: 16 pages, Revtex, 9 figures, 33 reference
Pairing properties of nucleonic matter employing dressed nucleons
A survey of pairing properties of nucleonic matter is presented that includes
the off-shell propagation associated with short-range and tensor correlations.
For this purpose, the gap equation has been solved in its most general form
employing the complete energy and momentum dependence of the normal self-energy
contributions. The latter correlations include the self-consistent calculation
of the nucleon self-energy that is generated by the summation of ladder
diagrams. This treatment preserves the conservation of particle number unlike
approaches in which the self-energy is based on the Brueckner-Hartree-Fock
approximation. A huge reduction in the strength as well as temperature and
density range of - pairing is obtained for nuclear matter as
compared to the standard BCS treatment. Similar dramatic results pertain to
pairing of neutrons in neutron matter.Comment: 15 pages, 10 figure
Pair condensation and bound states in fermionic systems
We study the finite temperature-density phase diagram of an attractive
fermionic system that supports two-body (dimer) and three-body (trimer) bound
states in free space. Using interactions characteristic for nuclear systems, we
obtain the critical temperature T_c2 for the superfluid phase transition and
the limiting temperature T_c3 for the extinction of trimers. The phase diagram
features a Cooper-pair condensate in the high-density, low-temperature domain
which, with decreasing density, crosses over to a Bose condensate of strongly
bound dimers. The high-temperature, low-density domain is populated by trimers
whose binding energy decreases toward the density-temperature domain occupied
by the superfluid and vanishes at a critical temperature T_c3 > T_c2.Comment: 11 pages, 4 figures, uses RevTex; v2: 12 pages, 4 figures, matches
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