abstract

The angular distribution for a quark scattering from the modes of the magnetic vacuum is calculated in the first approximation. One finds different behaviors of the light and heavy quarks. Similarities to the fast moving electron in a ionic crystal (polaron) are pointed out.

abstract

The decrease of vector meson masses with the pion decay constant for increasing baryon density, \(m^*_V/m_V = f^*_{\pi }/f_{\pi }\), is related to scaling properties of the Skyrme Lagrangian. Experimental data sensitive to vector meson properties in nuclei, such as K\(^{+}\) scattering and (e,e\(^{\prime }\),p) reactions, are shown to be compatible with the above relation.

abstract

We discuss the current status of the deuteron matter radius. We compare the deuteron \(A(q^2)\) structure function from the recent Saclay elastic electron–deuteron scattering experiment (S. Platchkov et al., Nucl. Phys. A510, 740 (1990)) and that from earlier Mainz data (G.G. Simon et al., Nucl. Phys. A364, 285 (1981)). The inconsistency of the two sets of data in the region of overlap is discussed in the light of a comparison with various deuteron potential models. The new experiment suggests a larger deuteron radius. We also analyse the Saclay fits to GEE, and deduce an implied value for the deuteron matter radius.

abstract

Time dependent Green’s function methods provide a basic theory for nuclear dynamics and transport-properties such as related e.g. to heavy ion collisions. In the static limit this theory is also applicable to hot as well as zero-temperature nuclei. Retarded Green’s functions are introduced in the non-equilibrium case while causal Green’s functions have been used extensively for calculating ground-state properties of nuclei as have the very similar Brueckner methods. The purpose of this paper is to point out and clarify differences (and similarities) between these methods. In addition to some formal differences there are those resulting from accepted methods of application. Errors caused by using free Green’s functions and related spectral-functions are pointed out. Only non-relativistic theories are discussed.

abstract

Ground state results for the hypernucleus \(^5_{\Lambda }\)He are reported. They have been calculated with a variational Jastrow-like trial wave function and also within the Diffusion Monte Carlo method. Simple central potentials have been used to describe NN and \(\Lambda \)N interactions. The validity of the rigid core approximation is discussed.

abstract

We have applied the microscopic coupled-cluster method (CCM) of many-body quantum theory to the U(1) lattice gauge models in (1+1) and (2+1) dimensions. The mode couplings and plaquette correlations are studied in detail by means of a hierarchical truncation scheme. Good numerical results for the ground-state energy have been obtained for a range of coupling constants varying from strong to weak. The systematic and nonperturbative natures of the CCM are emphasized.

abstract

A new version of the supersymmetry scheme for nuclei 32 \(\leq A \lt \) 40 has been proposed. The IBM bosons (pairs of nucleons approximately) have been taken with spin and isospin degrees of freedom (IBM4) while nucleons (nucleon) are bounded to the \(j = \) \({}^3\!/\!{}_2\) level only. The assumed supersymmetry group is then the unitary–unitary supergroup U(36/8). Theoretical energy levels and \(E2\) transition probabilities have been compared with experimental data yielding quite a good agreement.

abstract

Knowledge of the symmetry energy of nuclear matter is crucial for the determination of many properties of matter at ultra high density. Its value determines the neutron drip density in the crust of neutron star. The symmetry energy determines the proton fraction in the neutron star matter at supranuclear density, and therefore turns out to be of a paramount importance for the rate of cooling of neutron stars. It determines also the response of neutron star matter to the deviations from chemical equilibrium, and enters explicitly the formula for the bulk viscosity of the neutron star matter.

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We show that the low energy expressions for the CGLN pion photoproduction invariant amplitudes when evaluated at threshold yield a 17% enhancement of the de Baenst \(\gamma p \to \pi ^0 p\) threshold electric dipole amplitude. One can recover the de Baenst result, to lowest two orders in \(m_{\pi }/m_N\), by assuming that the Goldberger–Treiman (GT) relation \(f_{\pi } g = m_{N}g_A\) is exact. However, accounting for the observed 5% GT discrepancy and the recent modifications of the Saclay and Mainz threshold data, and comparing the data to the enhanced de Baenst amplitude leads to a large explicit breaking of chiral symmetry. The magnitude of the explicit chiral symmetry breaking is not cleanly extracted from the threshold data because of the GT-like cancellations in the exact \(\gamma p \to \pi ^0 p\) threshold electric dipole amplitude.

abstract

The square of the deuteron matter radius divided by the square of the scattering length can be expanded in powers of a parameter proportional to the effective range at the deuteron pole. The coefficients of this expansion beyond second order depend on the shape of the potential. We consider the third and fourth order terms for several simple potentials, both local and separable.

abstract

An account is given of a simplified relativistic approach for the study of single-particle energies for neutrons in nuclei and for a \(\Lambda \)-particle in hypernuclei and also for their average variation with the mass number. The analysis is based on the Dirac equation with scalar potential and fourth component of vector potential, which are assumed to be of rectangular shapes with the same radius. The energy eigenvalue equation is obtained analytically for every bound state, as well as the large and small component of the wave function. Attempts are also made to derive in certain cases approximate analytic expressions for the single particle energies as functions of the mass number. Numerical results, mainly for hypernuclei, are finally given and discussed.

abstract

A method of finding the exact solutions to the general two-body nuclear Hamiltonian is developed. It is based on the theory of Lie algebras of special orthogonal group. The algebraic structure of the model is discussed in details and the simplifications carried by the group theoretical approach are pointed out.

abstract

Mixing of nuclear states with different spins in external magnetic fields is briefly discussed. A case of special interest is the \(^{229}\)Th nucleus because of its 4.5(1) eV 3/2\(^+\) excited state which may mix with the 5/2\(^+\) ground state. Magnetic hfs and mixing of these states are calculated in cases of single electron and muonic atoms. Chances of experimental detection are considered.

abstract

The Momentum Sum Rule in deep inelastic scattering on nuclei is discussed and limitations of nuclear convolution model are pointed out. The pion and vector meson contributions to the nuclear structure function are derived from the composite picture of the nucleon in the nuclear medium and presented as correction to the nuclear convolution with nucleon degrees of freedom. Finite size effects of a nucleus are discussed.

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The half-diagonal two-body density matrix \(\rho _2(r_1, r_2, r^{\prime }_1, r^{\prime }_2)\) is studied in infinite nuclear matter, based on Jastrow-Slater ground-state trial functions. The associated generalized momentum distribution \(n({\bf p}, {\bf Q})\), related to the half-diagonal version of \(\rho _2\) by Fourier transformation in the variables \(r_1 - r^{\prime }_1\) and \(r_1 - r_2\), is calculated for three representative models of nuclear matter containing central correlations. The available numerical results correspond to (a) approximation in lowest (two-body) cluster order of a straightforward cluster expansion of the generalized momentum distribution, and (b) evaluation, to lowest cluster order, of form factors and other ingredients of a re-summed structural expression for \(n({\bf p}, {\bf Q})\) that collects the effects of different virtual scattering processes in the many-body medium. Dynamical correlations produce significant departures from the reference case of an ideal Fermi gas. The results should give an adequate picture of the behavior of \(n({\bf p}, {\bf Q})\) in certain limiting domains of the momenta \({\bf p}\) and \({\bf Q}\) where the short-range correlations dominate the complicated effects arising from the state-dependence of the interaction.

abstract

Role of the dimension of the deformation space admitted in the analysis of the spontaneous-fission half-life is studied by the example of even–even heavy nucleus \(^{260}\)106. Importance of taking sufficiently large dimension is demonstrated.