An effective lagrangian with broken scale and chiral symmetry IV: Nucleons and mesons at finite temperature

We study the finite temperature properties of an effective chiral Lagrangian which describes nuclear matter. Thermal fluctuations in both the nucleon and the meson fields are considered. The logarithmic and square root terms in the effective potential are evaluated by expansion and resummation with the result written in terms of the exponential integral and the error function, respectively. In the absence of explicit chiral symmetry breaking a phase transition restores the symmetry, but when the pion has a mass the transition is smooth. The nucleon and meson masses as a functions of density and temperature are discussed.     

Self-consistent and optical potentials for nucleons at positive and negative energies

The properties of the Hartree-Fock potential that coincides with the self-consistent potential and with the real part of the optical potential for nucleons in the case of a global regime of averaging are investigated by consistently taking into account the velocity-dependent components of nucleon-nucleon forces and nonlocality effects. For the first time, the properties of the effective energy-dependent Hartree-Fock potential are analyzed at negative nucleon energies. It is shown that the form of this potential undergoes a significant change upon reversal of the sign of nucleon energy. The conditions of applicability of the semiclassical approximation are found.     

Nucleon structure on the lattice

A few chosen nucleon properties are described from a lattice QCD perspective: the nucleon sigma term and the scalar strangeness in the nucleon; the vector form factors in the nucleon, including the vector strangeness contribution, as well as parity breaking effects like the anapole and electric dipole moment; and finally the axial and tensor charges of the nucleon. The status of the lattice calculations is presented and their potential impact on phenomenology is discussed.     

On the Coupling of φ Meson to Nucleons and Backward φ Production

Some analyses of the electromagnetic form factors of the nucleon and some analyses of the nucleon-nucleon potential favor a large coupling of the φ meson to nucleons. This is frequently quoted by advocates of a large ss component of the nucleon. It is shown that such large OZI-violating couplings are incompatible with data on φ production in backward direction via nucleon exchange.     

Some Aspects of Nuclear Structure in Relativistic Approach

The nucleon effective interaction in the nuclear medium is investigated in the framework of the DiracBrueckner-Hartree-Fock (DBHF) approach. A new decomposition of the Dirac structure of nucleon self-energy in the DBHF is adopted for asymmetric nuclear matter. The properties of finite nuclei are investigated with the nucleon effective interaction. The agreement with the experimental data is satisfactory. The relativistic microscopic optical potential in asymmetric nuclear matter is investigated in the DBHF approach. The proton scattering from nuclei is calculated and compared with the experimental data. A proper treatment of the resonant continuum for exotic nuclei is studied. The width effect of the resonant continuum on the pairing correlation is discussed. The quasiparticle relativistic random phase approximation based on the relativistic mean-field ground state in the response function formalism is also addressed.     

Transversity of quarks in a nucleon

The transversity distribution of quarks in a nucleon is one of the three fundamental distributions, that characterize nucleon's properties in hard scattering processes at leading twist (twist 2). It measures the distribution of quark transverse spin in a nucleon polarized transverse to its (infinite) momentum. It is a chiral-odd twist-two distribution function — gluons do not couple to it. Quarks in a nucleon/hadron are relativistically bound and transversity is a measure of the relativistic nature of bound quarks in a nucleon. In this work, we review some important aspects of this less familiar distribution function which has not been measured experimentally so far.     

Some Aspects of Nuclear Structure in Relativistic Approach

The nucleon effective interaction in the nuclear medium is investigated in the framework of the DiracBrueckner-Hartree-Fock (DBHF) approach. A new decomposition of the Dirac structure of nucleon self-energy in the DBHF is adopted for asymmetric nuclear matter. The properties of finite nuclei are investigated with the nucleon effective interaction. The agreement with the experimental data is satisfactory. The relativistic microscopic optical potential in asymmetric nuclear matter is investigated in the DBHF approach. The proton scattering from nuclei is calculated and compared with the experimental data. A proper treatment of the resonant continuum for exotic nuclei is studied. The width effect of the resonant continuum on the pairing correlation is discussed. The quasiparticle relativistic random phase approximation based on the relativistic mean-field ground state in the response function formalism is also addressed.     

Binding energies and modelling of nuclei in semiclassical simulations

We study the binding energies of spin–isospin saturated nuclei with nucleon number 8?A?100$8?A?100$ in semiclassical Monte Carlo many-body simulations. The model Hamiltonian consists of (i) nucleon kinetic energy, (ii) a nucleon–nucleon interaction potential, and (iii) an effective Pauli potential which depends on density. The basic ingredients of the nucleon–nucleon potential are a short-range repulsion, and a medium-range attraction. Our results demonstrate that one can always expect to obtain the empirical binding energies for a set of nuclei by introducing a proper density dependent Pauli potential in terms of a single variable, the nucleon number, A. The present work shows that in the suggested procedure there is a delicate counterbalance of kinetic and potential energetic contributions allowing a good reproduction of the experimental nuclear binding energies. This type of calculations may be of interest in further reproduction of other properties of nuclei such as radii and also exotic nuclei.     

THE PROPERTIES OF NUCLEAR MATTER AT LOW TEMPERATURE IN A POSSIBLE QUARK MECHANISM

In this paper,the nucleon is described by the MIT bag model,and the internal quark motion in the nucleon is modified by the scalar and vector meson fields.The Fermi motion of nucleon in nuclear matter is considered.The changes for intrinsic properties of nucleon in nuclear matter at different temperature are calculated as a function of the density.The binding energy per nucleon for different temperature is given.     

Nuclear Potential and Fusion Cross Sections for Synthesizing Super-Heavy Elements in Di-nuclear Systems

A double foMing method with simplified Skyrme-type nucleon nucleon interaction is used to calculate the nuclear interaction potential between two nuclei. The calculation is performed in tip-to-tip orientation of the two nuclei if they are deformed. Based on this method, the potential energy surfaces~ the fusion probabilities and the evaporation residue cross sections for some cold fusion reactions leading to super-heavy elements within di-nuclear system model are evaluated. It is indicated that after the improvement, the exponential decreasing systematics of the fusion probability with increasing charge number of projectile on the Pb based target become better and the evaporation residue cross sections are in better agreement with the experimental data.     

超重核合成时的驱动势与热熔合反应截面

在双核模型框架下,双核系统生成超重复合核的机理是由双核中的弹核的核子全部转移到靶核产生的,而核子转移是由双核系统驱动势确定的.对有的反应道,核子转移与中质比变化路径之间有比较复杂的关系.原则上动力学方程与驱动势都应该是中子和质子的二维显函数.为处理方便,采用与中质比相关的核子转移路径的选择来取驱动势,得到了接近实验值的超重核合成蒸发剩余截面. 关键词： 超重核 熔合反应 驱动势 激发函数     

Hard exclusive meson production and nonforward parton distributions

We present an analysis of twist-2, leading order QCD amplitudes for hard exclusive leptoproduction of mesons in terms of double/nonforward parton distribution functions. After reviewing some general features of nonforward nucleon matrix elements of twist-2 QCD string operators, we propose a phenomenological model for quark and gluon nonforward distribution functions. The corresponding QCD evolution equations are solved in the leading logarithmic approximation for flavor nonsinglet distributions. We derive explicit expressions for hard exclusive , , and neutral vector meson production amplitudes and discuss general features of the corresponding cross sections. Received: 12 November 1997 / Published online: 26 February 1998     

Nonlocality in the Nucleon-Nucleon Interaction Due to Minimal-Relativity Factors: Effects on Two-Nucleon Observables and the Three-Nucleon Binding Energy

Minimal-relativity factors, when multiplied to a static local mesonexchange nucleon-nucleon potential, lead to a nonlocal potential. It is shown that the nonlocality can be represented by an analytically given nonlocality function, which has a width inversely proportional to the nucleon mass and which tends towards δ(r − r), the usual locality condition, in the limit of the nucleon mass going to infinity. Consequences of this particular type of non-locality for two-nucleon observables and for the three-nucleon binding energy are investigated along with a Malfliet-Tjjon-type potential. After readjusting the potential parameters of the nonlocal potential such that its two-nucleon properties are well matched to the ones of the static local potential the effect of the nonlocality on the three-nucleon binding energy essentially vanishes. Received October 9, 1995; revised December 30, 1995; accepted for publication March 12, 1996     

Strange quark content in the nucleon

Though none of the experimental evidences for the strange quark contributions to nucleon properties is explained convincingly by an alternative, the recent experiments, even HAPPEX Collab. and A4 Collab., on a measurement of the parity-violating asymmetries show no strangeness in the proton. Despite this conclusion we demonstrate here no accidental compatibility of our theoretical predictions for nucleon strange form factors with some nonzero parity violation experimental results which strengthens our belief in the strangeness in the nucleon.     

Static observables of relativistic three-fermion systems with instantaneous interactions

We show that static properties like the charge radius and the magnetic moment of relativistic three-fermion bound states with instantaneous interactions can be formulated as expectation values with respect to intrinsically defined wave functions. The resulting operators can be given a natural physical interpretation in accordance with relativistic covariance. We also indicate how the formalism may be generalized to arbitrary moments. The method is applied to the computation of static baryon properties with numerical results for the nucleon charge radii and the baryon octet magnetic moments. In addition, we make predictions for the magnetic moments of some selected nucleon resonances and discuss the decomposition of the nucleon magnetic moments in contributions of spin and angular momentum, as well as the evolution of these contributions with decreasing quark mass.     

Phase transition and the nucleon as a soliton in the Nambu-Jona-Lasinio model at finite temperature and density

We study some bulk thermodynamical characteristics, meson properties and the nucleon as a baryon-number-one soliton in hot quark matter in the NJL model as well as in hot nucleon matter in a hybrid NJL model in which the Dirac sea of quarks is combined with a Fermi sea of nucleons. In both cases, working in the mean-field approximation, we find a chiral phase transition from the Goldstone to the Wigner phase. At finite density the chiral order parameter and the constituent quark mass have a non-monotonic temperature dependence — at finite temperatures not close to the critical one they are less affected than in cold matter. Whereas quark matter is rather soft against thermal fluctuations and the corresponding chiral phase transition is smooth, nucleon matter is much stiffer and the chiral phase transition is very sharp. The thermodynamical variables show large discontinuities which is an indication for a first-order phase transition. We solve the B = 1 solitonic sector of the NJL model in the presence of external hot quark and nucleon media. In the hot medium at intermediate temperature the soliton is more bound and less swelled than in the case of cold matter. At some critical temperature, which for nucleon matter coincides with the critical temperature for the chiral phase transition, we find no more a localized solution. According to this model scenario one should expect a sharp phase transition from nucleon to quark matter.     

The Triton from the Reid93 Potential in the UPA

The unitary pole approximation (UPA) provides an effective means to construct a rank one separable potential for calculations in which one requires a simple representation of the deuteron and/or triton ground-state wave function. By construction the deuteron wave function and the ¹S₀ anti-bound state wave function of the original potential are reproduced. We report results for the corresponding triton ground state. We choose to utilize the realistic Reid93 potential for this purpose. The Reid93 potential, generated by the Nijmegen group, is a Reid-like, partial-wave local potential that produces a χ² representation of the nucleon–nucleon (NN) scattering data that is as precise as an NN partial-wave analysis. Results for properties of ²H and ³H from the UPA are compared with those for the original potential. To further illustrate the precision of the method, results for properties of the deuteron and triton from the UPA are also compared with those for the original Reid68 potential.