共查询到20条相似文献,搜索用时 0 毫秒
1.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):161-167
The parameters of the σ-ω-ρ model in the relativistic mean-field theory with nonlinear σ-meson self-interaction are determined
by nuclear-matter properties, which are taken as those extracted by fits to data based on nonrelativistic nuclear models.
The values of the relevant parameters are C
σ
2∼ 94, C
ω
2∼ 32, C
ρ
2∼ 26, b∼ - 0.09, c∼ 1, and the σ-meson mass m
σ∼ 370 MeV, while the value of the calculated nuclear- surface thickness is t∼ 1.4 fm. The field system is shown to be stable, since the σ-meson self-interaction energy is a lower bound in this whole
parameter region with positive c. On the other hand, the effective nucleon mass M* is larger than 0.73M, if the symmetry incompressibility Ks is assumed to be negative and the nuclear-matter incompressibility K0 is kept less than 300 MeV.
Received: 27 June 2001 / Accepted: 5 October 2001 相似文献
2.
We present a calculation of the neutrino-nucleon scattering cross-section which takes into account the nuclear correlations
in the relativistic random phase approximation (RPA). Our approach is based on a quantum-hadrodynamics model with exchange
of σ, ω, π, ρ and δ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and proto-neutron
star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and
temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor
channel, coupling to the delta-meson and meson mixing. In contrast with the results of other authors, we find that the neutral-current
process is not sensitive to the strength g' of the residual contact interaction. As a consequence, it is found that RPA corrections with respect to the mean-field approximation
amount to only 10% to 15% at high density.
Received: 27 June 2001 / Accepted: 14 January 2002 相似文献
3.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):137-141
The σ-ω coupling is introduced phenomenologically in the linear σ-ω model to study the nuclear matter properties. It is shown
that not only the effective nucleon mass M* but also the effective σ meson mass m
σ
* and the effective ω meson mass m
ω
* are nucleon-density-dependent. When the model parameters are fitted to the nuclear saturation point, with the nuclear radius
constant r
0 = 1.14 fm and volume energy a
1 = 16.0 MeV, as well as to the effective nucleon mass M
* = 0.85M, the model yields m
σ
* = 1.09m
σ and m
ω
* = 0.90m
ω at the saturation point, and the nuclear incompressibility K
0 = 501 MeV. The lowest value of K0 given by this model by adjusting the model parameters is around 227 MeV.
Received: 23 March 2001 / Accepted: 8 June 2001 相似文献
4.
C. Y. Ryu C. H. Hyun S. W. Hong B. K. Jennings 《The European Physical Journal A - Hadrons and Nuclei》2005,24(1):149-157
We investigate the properties of the neutron star with relativistic mean-field models. We incorporate in the quantum hadrodynamics and in the quark-meson coupling models a possible reduction of meson masses in nuclear matter. The equation of state for neutron star matter is obtained and is employed in Oppenheimer-Volkov equation to extract the maximum mass of the stable neutron star. We find that the equation of state, the composition and the properties of the neutron stars are sensitive to the values of the meson masses in medium. 相似文献
5.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献
6.
T. Takatsuka S. Nishizaki Y. Yamamoto 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):213-215
Neutron star models with hyperon-mixed core are studied by a realistic approach to use the YN and the YY interactions consistent
with hypernuclear data. From the compatibility of the theoretical maximum mass with the observed neutron star mass 1.44 M
⊙ of PSR1913+16, the necessity of some extra repulsion in hypernuclear systems, e.g., a repulsion from three-body force, is stressed. It is noted that the increase of baryon degrees of freedom to avoid the
short-range repulsion effectively is an essential mechanism causing the Y-mixed phase.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
7.
J.E. Amaro M.B. Barbaro J.A. Caballero T.W. Donnelly A. Molinari 《The European Physical Journal A - Hadrons and Nuclei》2002,15(4):421-427
The impact of Hartree-Fock correlations on the nuclear momentum distribution is studied in a fully relativistic one-boson-exchange
model. Hartree-Fock equations are exactly solved to first order in the coupling constants. The renormalization of the Dirac
spinors in the medium is shown to affect the momentum distribution, as opposed to what happens in the non-relativistic case.
The unitarity of the model is shown to be preserved by the present renormalization procedure.
Received: 7 June 2002 / Accepted: 24 September 2002 / Published online: 10 December 2002
RID="a"
ID="a"e-mail: juan@nucle.us.es
Communicated by G. Orlandini 相似文献
8.
J. F. Gu H. Guo X. G. Li Y. X. Liu F. R. Xu 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):455-460
Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic
model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for
the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with
a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color
superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired
quark matter. The K0 condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and
the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass ms and the color superconducting gap Δ. Increasing B and ms or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars. 相似文献
9.
P. Bożek 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):325-328
Symmetric nuclear matter is studied within the conserving, self-consistent T-matrix approximation. This approach involves off-shell propagation of nucleons in the ladder diagrams. The binding energy
receives contributions from the background part of the spectral function, away from the quasiparticle peak. The Fermi energy
at the saturation point fulfills the Hugenholz-Van Hove relation. In comparison to the Brueckner-Hartree-Fock approach, the
binding energy is reduced and the equation of state is stiffer.
Received: 16 April 2002 / Accepted: 10 June 2002 / Published online: 26 November 2002
RID="a"
ID="a"e-mail: bozek@sothis.ifj.edu.pl
Communicated by A. Molinari 相似文献
10.
M. Baldo E. E. Saperstein S. V. Tolokonnikov 《The European Physical Journal A - Hadrons and Nuclei》2007,32(1):97-108
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. 相似文献
11.
In the framework of the relativistic mean field theory, the effects of the δ meson on protoneutron star matter with hyperons at finite temperature are investigated. In thermal protoneutron star matter, the δ field potential increases with density first and then decreases. Fixing the density, the increase of the temperature suppresses the δ field potential. With the inclusion of the δ meson, the threshold densities for hyperons become lower and the abundance of trapped neutrinos decreases. The most important effect of the δ meson is to increase the abundance of hyperons in the inner core range of protoneutron stars. With the rise of the temperature, the density range where the δ meson plays an important role is narrowed and the effects of the δ meson are suppressed. Moreover, the protoneutron star mass and radius are nearly not affected by the δ meson 相似文献
12.
We investigate the relation between the binding energy and the Fermi energy and between different expressions for the pressure
in cold nuclear matter. For a self-consistent calculation based on a Φ derivable T-matrix approximation with off-shell propagators, the thermodynamic relations are well satisfied unlike for a G-matrix or a T-matrix approach using quasi-particle propagators in the ladder diagrams.
Received: 8 February 2001 / Accepted: 11 June 2001 相似文献
13.
We extend a recent chiral approach to nuclear matter of Lutz et al.Phys. Lett. B 474, 7 (2000)) by calculating the underlying (complex-valued) single-particle potential U(p, k
f) + iW(p, k
f). The potential for a nucleon at the bottom of the Fermi sea, U(0, k
f0) = - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy
does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi surface. Also, the imaginary single-particle potential, W(0, k
f0) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear-matter equation of state
can be obtained if the short-range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1π-exchange). We also consider the equation of state of pure neutron matter ˉEn(k
n) and the asymmetry energy A(k
f) in that approach. The downward bending of these quantities above nuclear-matter saturation density seems to be a generic
feature of perturbative chiral pion-nucleon dynamics.
Received: 19 December 2002 / Accepted: 11 February 2003 / Published online: 15 April 2003 相似文献
14.
Neutron stars with isovector scalar correlations 总被引:1,自引:0,他引:1
Neutron stars with the isovector scalar δ-field are studied in the framework of the relativistic mean-field (RMF) approach in a pure-nucleon-plus-lepton scheme. The δ-field leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses. Both features are influencing the stability conditions of the neutron stars. Two parametrizations for the effective nonlinear Lagrangian density are used to calculate the nuclear equation of state (EOS) and the neutron star properties, and compared to correlated Dirac-Brueckner results. We conclude that in order to reproduce reasonable nuclear structure and neutron star properties within a RMF approach, a density dependence of the coupling constants is required. 相似文献
15.
G. Krein R.S. Marques de Carvalho D.P. Menezes M. Nielsen M.B. Pinto 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):45-53
The optimized δ-expansion is a nonperturbative approach for field theoretic models which combines the techniques of perturbation
theory and the variational principle. This technique is discussed in the λφ4 model and then implemented in the Walecka model for the equation of state of nuclear matter. The results obtained with the
δ expansion are compared with those obtained with the traditional mean field, relativistic Hartree and Hartree-Fock approximations.
Received: 17 March 1997 / Revised version: 27 August 1997 相似文献
16.
Response functions in nuclear matter at finite temperature are considered beyond the usual Hartree-Fock plus random phase approximation (RPA) scheme. The contributions due to the propagator for the dressed nucleons and the corresponding vertex corrections are treated in a consistent way. For that purpose a semi-realistic Hamiltonian is developed with parameters adjusted to reproduce the nucleon self-energy as derived from realistic nucleon-nucleon interactions. For a scalar residual interaction the resulting response functions are very close to the RPA response functions. However, the collective modes, if present, get an additional width due to the coupling to multi-pair configurations. For isospin-dependent residual interactions we find strong modifications of isospin response functions due to multi-pair contributions in the response function. Such a modification can lead to the disappearance of collective spin or isospin modes in a correlated system and shall have an effect on the absorption rate of neutrinos in nuclear matter. 相似文献
17.
J. Piekarewicz 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):537-541
The neutron radius of a heavy nucleus is a fundamental nuclear-structure observable that remains elusive. Progress in this
arena has been limited by the exclusive use of hadronic probes that are hindered by large and controversial uncertainties
in the reaction mechanism. The parity radius experiment at the Jefferson Laboratory offers an attractive electro-weak alternative
to the hadronic program and promises to measure the neutron radius of 208Pb accurately and model independently via parity-violating electron scattering. In this contribution we examine the far-reaching
implications that such a determination will have in areas as diverse as nuclear structure, atomic parity violation, and astrophysics. 相似文献
18.
The density-dependent relativistic hadron (DDRH) field theory proposed recently is extended to investigate the longitudinal response function and the Coulomb sum rule in quasielastic electron scattering in the relativistic random phase approximation (RPA). The results in the DDRH model are compared with those in other models systematically. It is found that meson effective masses induced by the nonlinear terms in the nonlinear Walecka model should be used to obtain the meson Greens functions when the longitudinal response function and the Coulomb sum rule are calculated. The effects of the and mesons are clearly shown in quasielastic electron scattering, and the isospin-dependent attractive potential between nucleons due to the exchange of the -meson cancels the isospin-dependent repulsive contribution of the -meson to a certain extent. The obtained results in the DDRH model are in good agreement with experimental data except for the Coulomb sum rule in 208Pb. 相似文献
19.
P. M. Milazzo G. Vannini M. Bruno N. Colonna M. D’Agostino F. Gramegna G. V. Margagliotti P. F. Mastinu A. Moroni 《The European Physical Journal A - Hadrons and Nuclei》2000,7(3):355-360
The dependence of the nuclear temperatures of highly excited systems, extracted by means of the double ratios of the emitted
isotopes, on the experimental conditions is investigated. Experimental data obtained in the Xe+Cu 30 MeV/nucleon reaction
are used to study the sensitivity of the method and the effects of the energy thresholds on the obtained temperature values.
We find that the temperatures extracted using the He/Li ratios can be strongly influenced by the experimental energy thresholds
which are different for different elements. These distortions depend on the velocity of the emitting system and on the detection
angle and therefore particular care is needed in the choice of the detectors in those experiments in which velocities are
low and angles are large. The use of four isotopes of the same element make negligible such effects.
Received: 6 October 1999 / Accepted: 28 May 2000 相似文献
20.
We perform a systematic calculation of the equation of state of asymmetric nuclear matter at finite temperature within the framework of the Brueckner-Hartree-Fock approach with a microscopic three-body force. When applying it to the study of hot kaon condensed matter, we find that the thermal effect is more profound in comparison with normal matter, in particular around the threshold density. Also, the increase of temperature makes the equation of state slightly stiffer through suppression of kaon condensation. 相似文献