IBM-1 calculations towards the neutron-rich nucleus 106^{106}Zr

The neutron-rich N=66 isotonic and A=106 isobaric chains, covering regions with varying types of collectivity, are interpreted in the framework of the interacting boson model. Level energies and electric quadrupole transition probabilities are compared with available experimental information. The calculations for the known nuclei in the two chains are extrapolated towards the neutron-rich nucleus $^{106}$Zr.Comment: 5 pages, 2 figures, 6 tables, to be published in Phys. Rev.

Re-analysis of the nucleon space- and time-like electromagnetic form factors in a two-component model

Recent experimental data on space-like and time-like form factors of the nucleon are analyzed in terms of a two-component model with a quark-like intrinsic three-quark structure and quark-antiquark pairs.Comment: 9 pages, 5 figures, accepted for publication as a Brief Report in Physical Review

Algebraic models of hadron structure: I. Nonstrange baryons

We introduce an algebraic framework for the description of baryons. Within this framework we study a collective string-like model and show that this model gives a good overall description of the presently available data. We discuss in particular masses and electromagnetic couplings, including the transition form factors that can be measured at new electron facilities.Comment: to be published in Annals of Physics (N.Y.), 44 pages of LaTex, 11 postscript figure files on request, UU-94-0

Two-level interacting boson models beyond the mean field

The phase diagram of two-level boson Hamiltonians, including the Interacting Boson Model (IBM), is studied beyond the standard mean field approximation using the Holstein-Primakoff mapping. The limitations of the usual intrinsic state (mean field) formalism concerning finite-size effects are pointed out. The analytic results are compared to numerics obtained from exact diagonalizations. Excitation energies and occupation numbers are studied in different model space regions (Casten triangle for IBM) and especially at the critical points.Comment: 14 pages, 13 figure

Quadrupole collectivity in random two-body ensembles

We conduct a systematic investigation of the nuclear collective dynamics that emerges in systems with random two-body interactions. We explore the development of the mean field and study its geometry. We investigate multipole collectivities in the many-body spectra and their dependence on the underlying two-body interaction Hamiltonian. The quadrupole-quadrupole interaction component appears to be dynamically dominating in two-body random ensembles. This quadrupole coherence leads to rotational spectral features and thus suggests the formation of the deformed mean-field of a specific geometry

Application of the coherent state formalism to multiply excited states

A general expression is obtained for the matrix element of an m-body operator between coherent states constructed from multiple orthogonal coherent boson species. This allows the coherent state formalism to be applied to states possessing an arbitrarily large number of intrinsic excitation quanta. For illustration, the formalism is applied to the two-dimensional vibron model [U(3) model], to calculate the energies of all excited states in the large-N limit.Comment: LaTeX (iopart); 10 pages; to be published in J. Phys.

Regular spectra in the vibron model with random interactions

The phenomenom of emerging regular spectral features from random interactions is addressed in the context of the vibron model. A mean-field analysis links different regions of the parameter space with definite geometric shapes. The results that are, to a large extent, obtained in closed analytic form, provide a clear and transparent interpretation of the high degree of order that has been observed in numerical studies.Comment: 19 pages, 8 figures, 2 tables. Physical Review C, in pres