g-Factors in the (sdg) boson model

The role of the g-boson in producing first-order variations in the g-factors of states in rotational nuclei is investigated. It is shown that the g-boson is unlikely to contribute directly to any observed g-factor variations in the ground-state band.     

sdg boson model in the SU(3) scheme

Basic properties of the interacting boson model with s-, d- and g-bosons are investigated in rotational nuclei. An SU(3)-seniority scheme is found for the classification of physically important states according to a group reduction chain U(15) ? SU(3). The capability of describing rotational bands increases enormously in comparison with the ordinary sd interacting boson model. The sdg boson model is shown to be able to describe the so-called anharmonicity effect recently observed in the ¹⁶⁸Er nucleus.     

Intrinsic states in the sdg interacting boson model

We give the intrinsic states explicitly in the boson representation in the framework of the sdg interacting boson model. Although they are only valid in the large-N limit, they are useful to estimate various physical quantities in well deformed nuclei. One can compare these results with those predicted in the IBM1 or in the IBM2.     

Proton-neutron sdg boson model and spherical-deformed phase transition

The spherical-deformed phase transition in nuclei is described in terms of the proton-neutron sdg interacting boson model. The sdg hamiltonian is introduced to model the pairing+quadrupole interaction. The phase transition is reproduced in this framework as a function of the boson number in the Sm isotopes, while all parameters in the hamiltonian are kept constant at values reasonable from the shell-model point of view. The sd IBM is derived from this model through the renormalization of g-boson effects.     

Improved description of M1 transitions by special hamiltonians of the proton-neutron interacting boson model

The proton-neutron interacting boson model (IBM-2) describes energies, B(E2) and B(M1) values of nuclei. In order to reduce the great number of free IBM-2 parameters two special IBM-2 hamiltonians are proposed which allow a decoupling of the energy and B(E2) fit from the determination of the B(M1) values and the energy of the lowest mixed symmetry 1⁺ state. This property allows a simple fit procedure of the IBM-2 parameters in both cases.     

sdg Interacting boson model: hexadecupole degree of freedom in nuclear structure

Thesdg interacting boson model (sdgIBM), which includes monopole (s), quadrupole (d) and hexadecupole (g) degrees of freedom, enables one to analyze hexadecupole (E4) properties of atomic nuclei. Various aspects of the model, both analytical and numerical, are reviewed emphasizing the symmetry structures involved. A large number of examples are given to provide understanding and tests, and to demonstrate the predictiveness of thesdg model. Extensions of the model to include proton-neutron degrees of freedom and fermion degrees of freedom (appropriate for odd mass nuclei) are briefly described. A comprehensive account ofsdgIBM analysis of all the existing data on hexadecupole observables (mainly in the rare-earth region) is presented, includingβ ₄ (hexadecupole deformation) systematics,B(IS4; 0 _GS ⁺ →4 _γ ⁺ ) systematics that give information about hexadecupole component in γ-vibration,E4 matrix elements involving few low-lying 4⁺ levels,E4 strength distributions and hexadecupole vibrational bands in deformed nuclei. The survey of literature for this review was concluded in December 1991.     

Finite-temperature phase transitions in a two-dimensional boson Hubbard model

We study finite-temperature phase transitions in a two-dimensional boson Hubbard model with zero-point quantum fluctuations via Monte Carlo simulations of a quantum rotor model and construct the corresponding phase diagram. Compressibility shows a thermally activated gapped behavior in the insulating regime. Finite-size scaling of the superfluid stiffness clearly shows the nature of the Kosterlitz-Thouless transition. The transition temperature T(c) confirms a scaling relation T(c) proportional, rho(0)(x), with x=1.0. Some evidence of anomalous quantum behavior at low temperatures is presented.     

Dyson-type boson mapping and SU(6) boson model

The Dyson-type boson mapping is applied to realistic cases to show that it is a very promising method for describing nuclear collective motion. Eigenvectors are obtained in the corresponding hermitian boson theory from the results of right- and left-hand-side eigenvalue problems in the Dyson boson theory. The numerical results are compared with those of the SU(6) boson model and exact quasiparticle shell-model calculations within the multi-phonon subspace.     

Description of spectrum and electromagnetic transitions in ~(94)Mo through the proton-neutron interacting boson model

We investigated the properties of low-lying states in ~(94)Mo within the framework of the proton-neutron interacting boson model(IBM-2), with special focus on the characteristics of mixed-symmetry states. We calculated level energies and M1 and E2 transition strengths. The IBM-2 results agree with the available quantitative and qualitative experimental data on ~(94)Mo. The properties of mixed-symmetry states can be well described by IBM-2 given that the energy of the d proton boson is different from that of the neutron boson, especially for the transition of B(M1, 4_2~+→ 4_1~+).     

Spectra and electromagnetic transitions of ~(72-84)Kr in the interacting boson model-1

Within the framework of the interacting boson model-1, the energy levels and electromagnetic transitions in ~(72-84)Kr isotopes are calculated. The structures of the eigenstate and Hamiltonian matrix for some low-lying states are also calculated. The calculated results are compared with available experimental data, and the results are generally in good agreement. The present study shows that the ~(72,74,76,80,82,84)Kr isotopes are in the transition from U(5)→ S U(3), and ~(78)Kr is in the transition from U(5)→O(6).     

Landau theory of shape phase transitions in the cranked interacting boson model

Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases.     

Z′ boson in theSO(10) model

TheSO(10) model is a candidate for the unification of electromagnetic, weak, and strong interactions. The range of theZ′ mass is 495 GeV<m _z′ <10⁹ GeV. The formulas for the width and asymmetry forZ′ decay depend only on theZ′ mass. We apply the method of Boudjemaet al. to identify a theoretical origin of theZ′ boson inSO(10) and compare with other models.     

E1 calculations in thesdf-interacting boson model

A simple IBA-sdf form for theE1 transition operator containing an one-body term and a two-body term is tested in a non-analytical case. TheE 1 transition probabilities in the rare-earth region are reproduced rather well.     

The fate of the U(1) goldstone boson

In the framework of a manifestly covariant formulation of (non-Abelian) gauge theories, we analyse what the gauge invariance (BRS invariance) implies for the problem of the Goldstone boson associated with the conserved U(1) axial vector current. Based on the symmetry consideration of gauge invariance only, it is shown that the Goldstone boson does not appear as a physical particle at all, if and only if the Faddeev-Popov (FP) ghost forms a massless bound state with the gauge boson in a pseudoscalar channel. This decoupling of the Goldstone boson from the physical sector is not caused by the Goldstone dipole proposed by Kogut and Susskind, but by a Goldstone quartet including the FP ghost bound state. This decoupling mechanism by the Goldstone quartet can be shown to become equivalent to that of the Goldstone dipole, only in a special case, i.e., the Schwinger model which is an Abelian theory in two dimensions. In the Abelian gauge theory in four dimensions, the chiral U(1) Goldstone boson necessarily appears as a physical particle.     

Schwinger boson mapping of SO(8) fermion model

The Schwinger representation of the SO(8) fermion pair algebra in terms ofd and quasispin vector (u, s, v) bosons is used in deriving a microscopic boson coherent state having both particle-hole and pair excitations. The coherent state is the exact boson image of the HFB variational solution. We can study the shape phase transition and pairing behaviour of the nuclear ground states using the coherent states.