Ground state properties of nuclear matter

The ground state properties of nuclear matter are calculated in theΛ ₁₁-approximation¹. A nucleon-nucleon interaction of the Yamaguchi-type and thes-wave part ofTabakin's potential have been considered. In both cases too large values for the density of nuclear matter and the binding energy per nucleon are found. The momentum distribution turns out to be very small for momenta larger than the Fermi momentum.     

Fermi-liquid properties of nuclear matter in a relativistic mean-field theory

The Fermi-liquid properties of the model nuclear system described by a relativistic quantum field theory are examined in terms of a relativistic extension of Landau's Fermi-liquid theory. The relativistic Landau parameters are derived microscopically from the ground state energy in the mean-field approximation, and are used to describe the thermodynamic properties of the system, such as the compressibility, the symmetry energy and the hydrodynamic sound velocities. We reproduce the previous results at nuclear saturation density (n₀ = 0.19 fm⁻³) and extrapolate to all density regions. It is shown that the system exhibits instability against the long wavelength density fluctuations in the low density region (n_B <0.70 n₀) and becomes stable at and above the nuclear saturation density due to the relativistic reduction of the attractive scalar meson component in the quasiparticle interaction. In the extreme high-density region, we reproduce the correct causal results for sound velocities. The existence of collisionless zero-sound oscillation is also examined.     

Saturating chiral field theory for the study of nuclear matter in the relativistic Hartree approximation

The bulk properties of nuclear matter are studied by considering a chirally invariant lagrangian which contains an interaction term involving scalar and vector mesons, of the form (apart from a numerical factor) used by Boguta. The calculation is performed in the relativistic Hartree approximation which includes the baryon vacuum fluctuation correction.     

Systematics of nuclear matter properties in a non-linear relativistic field theory

The properties of symmetric nuclear matter are investigated in a phenomenological non-linear relativistic field theory of nuclear matter. A mean field approximation is made. We find that the equation of state over a considerable density range is determined by the nuclear matter compressibility modulus. A family of equations of state is considered that fit all known bulk properties of nuclear matter, including the energy dependence of the optical potential. The importance of non-Yukawa type nuclear interactions is discussed.     

Hot metastable state of abnormal matter in relativistic nuclear field theory

Because of their non-linearity, the field equations of relativistic nuclear field theory admit of additional solutions besides the normal state of matter. One of these is a finite-temperature abnormal phase. Over a narrow range in temperature, matter can exist in the abnormal phase at zero pressure. This is a hot metastable state, for which there is a barrier against decay, because the field configuration is different than in the normal state, the baryon masses are far removed from their vacuum masses, there is an abundance of pairs also far removed from their vacuum masses, and a correspondingly high entropy. The abundance of baryon-antibaryon pairs is the glue that holds this matter together. The signals associated with this novel state are quite unusual. A fragment of such matter will cool by emitting a spectrum of black-body radiation, consisting principally of photons, lepton pairs and pions, rather than by baryon emission, because the latter are far removed from their vacuum masses. If produced at the upper end of its temperature range, a large fraction of the original energy, more than half in the examples studied here, is radiated in this way. The baryons and light elements produced in the eventual decay, after the abnormal matter has cooled to a domain where its pressure becomes positive, will account for only a fraction of the original energy. The energy domain of this state depends sensitively on the coupling constants, and within a reasonable range as determined by nuclear matter properties, can lie in the range of GeV to tens of GeV per nucleon.     

Pion condensation in a relativistic field theory consistent with bulk properties of nuclear matter

Pion condensation has not previously been investigated in a theory that accounts for the known bulk properties of nuclear matter, its saturation energy and density and compressibility. We have formulated and solved self-consistently, in the mean field approximation, a relativistic field theory that possesses a condensate solution and reproduces the correct bulk properties of nuclear matter. The theory is solved in its relativistically covariant form for a general class of space-time dependent pion condensates. Self-consistency and compatibility with bulk properties of nuclear matter turn out to be very stringent conditions on the existence and energy of the condensate, but they do allow a weak condensate energy to develop. The spin-isospin density oscillations, on the other hand, can be large. It is encouraging, as concerns the possible existence of new phases of nuclear matter, that this is so, unlike the Lee-Wick density isomer, that appears to be incompatible with nuclear matter properties.     

Nucleon-nucleus optical potential in a relativistic theory of nuclear matter

From a relativistic model of nuclear matter the optical potentials for nucleon scattering from ⁴⁰Ca and ⁹⁰Zr are obtained. These potentials are derived from the properties of the target nucleus and are essentially universal. This means that the integrated strength of the optical potential $\text{J}{}_{\mathrm{A}}\text{= (}\text{1}\text{A}\text{) ∫}\text{d}{}^3\text{r U}{}_{\mathrm{<mtext>op</mtext>}}\text{(r)}$ is very weakly dependent on A. The optical potential for antiparticle-nucleus scattering is also computed.     

Properties of nuclear and neutron matter in a relativistic Hartree-Fock theory

Relativistic Hartree-Fock (HF) equations are derived for an infinite system of mesons and baryons in the framework of a renormalizable relativistic quantum field theory. The derivation is based on a diagrammatic approach and Dyson's equation for the baryon propagator. The result is a set of coupled, nonlinear integral equations for the baryon self-energy with a self-consistency condition on the single-particle spectrum. The HF equations are solved for nuclear and neutron matter in the Walecka model, which contains neutral scalar and vector mesons. After renormalizing model parameters to reproduce nuclear matter saturation properties, HF results at low to moderate densities are similar to those in the mean-field (Hartree) approximation. Self-consistent exchange corrections to the Hartree equation of state become negligible at high densities. Rho- and pi-meson exchanges are incorporated using a renormalizable gauge-theory model. A chiral transformation of the lagrangian is used to replace the pseudoscalar πN coupling with a pseudovector coupling, for which one-pion exchange is a reasonable first approximation. This transformation maintains the model's renormalizability so that corrections may be evaluated. Pion exchange has a small effect on the HF results of the Walecka model and brings HF results in closer agreement with the mean-field theory. The diagrammatic techniques used here retain the mesonic degrees of freedom and are simple enough to be extended to more refined self-consistent approximations.     

相对论平均场理论对Rn同位素链原子核基态性质的研究

在相对论平均场理论的框架下,对Rn同位素链原子核的结合能、形变、同位素位移等若干基态性质进行了较详细的研究.结果表明,理论计算结果与已有的实验数据符合较好.原子核的四极形变主要出现在远离幻数的区域(N=110-124和N=129-142).而在中子数大于幻数的区域(N=127-142),十六级形变也非常明显.对电荷半径的研究显示,Rn同位素链的同位素位移曲线的斜率在中子幻数处出现明显的变化. 关键词： 相对论平均场理论 电荷半径 同位素位移 单粒子能级     

An equation of state for nuclear and higher-density matter based on relativistic mean-field theory

A model stress tensor for high-density matter based on a linearized relativistic quantum field theory is examined. The two coupling constants are fit to nuclear matter. Other properties of nuclear and neutron matter and neutron stars are then implied.     

Ground state properties of La isotopes in reflection asymmetric relativistic mean field theory

The ground state properties of La isotopes are investigated with the reflection asymmetric relativistic mean field(RAS-RMF) model.The calculation results of binding energies and the quadrupole moments are in good agreements with the experiment.The calculation results indicate the change of the quadrupole deformation with the nuclear mass number.The "kink" on the isotope shifts is observed at A = 139 where the neutron number is the magic number N = 82.It is also found that the octupole deformations may exist...     

Nuclear matter properties and relativistic mean-field theory

Nuclear matter properties are calculated in the relativistic mean-field theory by using a number of different parameter sets. The result shows that the volume energy a₁ and the symmetry energy J are around the acceptable values 16MeV and 30MeV, respectively; the incompressibility K₀ is unacceptably high in the linear model, but assumes reasonable value if nonlinear terms are included; the density symmetry L is around 100MeV for most parameter sets, and the symmetry incompressibility K _s has positive sign which is opposite to expectations based on the nonrelativistic model. In almost all parameter sets there exists a critical point (,), where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero, falling into ranges 0.014fm^-3 < < 0.039fm^-3 and 0.74 < ≤0.95; for a few parameter sets there is no critical point and the pure neutron matter is predicted to be bound. The maximum mass M _NS of neutron stars is predicted in the range 2.45M ?M _NS? 3.26M , the corresponding neutron star radius R _NS is in the range 12.2km ?R _NS? 15.1km. Received: 5 May 2000 / Accepted: 28 November 2000     

First observation of nuclear rainbow scattering in 16O + 40Ca system

Measurements of the differential cross section of the ¹⁶O + ⁴⁰Ca elastic scattering at the ¹⁶O energy 214 MeV were performed. For the first time, nuclear rainbow scattering in the ¹⁶O + ⁴⁰Ca system was observed. The analysis shows that the 45° minimum in the angular distribution could be identified as an Airy supernumerary one, probably, of the third order. It corresponds to a distance of closest approach of the colliding nuclei less than 3 fm. The text was submitted by the authors in English.     

Effects of nuclear structure in double charge exchange reactions on 16O and 40Ca

The energy dependence of forward double charge exchange (DCX) reaction is studied for the doubly closed shell nuclei ¹⁶O and ⁴⁰Ca. A common characteristic of the two DCX reactions is a resonance-like peak around 50 MeV pion lab energy. While some authors have interpreted this peak as the evidence of a dibaryon resonance state, we show that it arises naturally in a two-step process in the conventional pion—nucleon system with proper handling of nuclear structure. The effects of nuclear structure are demonstrated through a comparison among different nuclear structure models: the symmetry model SU(4) ? SU(3), the single particle shell model and the «realistic” shell model.     

Hartree theory for matter in a photon or phonon field

For a Dicke-type Hamiltonian describing M two-level systems coupled to N modes of a Boson field, the expectation value is minimized with respect to unrestricted products of 2^M-level states and field states. In the resulting Hartree ground state(s) ? ? Π, ? is ground state of a cubic Schrödinger equation in $\text{C}$^2M and Π is the product of N coherent one-mode states depending on ?. It is proved that ? factorizes as well, into M two-level states determined by a nonlinear equation in $\text{R}$^M; that for weak coupling the Hartree ground state is unique and independent of the parameters in H; and that for strong coupling there are consecutively 2,…,2^L (and possibly even more) Hartree ground states where 1≤L≤min{M, 2N} counts certain reflection symmetries. Details of this symmetry-breaking bifurcation (such as structural stability of relaxed two-level systems) and connections to the true ground state(s) of H are worked out.     

Ground state correlation effects on the Gamow-Teller strength distribution in 48Ca

We calculate the Gamow-Teller strength distribution in ⁴⁸Ca using an extended second RPA which explicitly includes ground state correlations. The following effects are taken into account: (i) the reduction of the 1p1h matrix elements due to the partial occupation of single-particle orbitals, (ii) the modification of the 1p1h Green function in the presence of ground state correlations and 2p2h correlations in the excited states, (iii) renormalization of the external field and (iv) the pure 2p2h response due to unblocking of the ground state. The first three effects largely cancel in the region of the Gamow-Teller resonance while the last two cancel at higher energies. The resulting strength distribution is therefore quite similar to the one obtained previously in second RPA.