arXiv subjects
Publications and source records attributed to R. Bijker.
Nuclear supersymmetry is reviewed and some of its applications and extensions are discussed, together with a proposal for new, more stringent and precise tests to probe the supersymmetry classification, in particular, correlations between nuclei that belong to the same supermultiplet. The combination of these theoretical and experimental studies may play a unifying role in nuclear phenomena
We discuss the spectroscopy of pentaquarks. The quantum numbers of the ground state depend on the interplay between spin-flavor and orbital contributions to the energy. The magnetic moments of the lowest pentaquark state with negative and positive parity are found to be 0.382 μ_N and 0.089 μ_n, respectively.
Extensions of nuclear supersymmetry are discussed, together with a proposal for new, more stringent and precise tests that probe the susy classification and specific two-particle correlations among supersymmetric partners. The combination of these theoretical and experimental studies may play a unifying role in nuclear phenomena.
New experimental tests of nuclear supersymmetry are suggested. They involve the measurement of one- and two-nucleon transfer reactions between nuclei that belong to the same supermultiplet. These reactions provide a direct test of the `fermionic' sector, i.e. of the operators that change a boson into a fermion or vice versa. We present some theoretical predictions for the supersymmetric quartet of nuclei: 194Pt, 195Pt, 195Au and 196Au.
Three-body clusters are studied in the algebraic cluster model. Particular attention is paid to the case of three identical particles. It is shown in a geometrical analysis that the harmonic oscillator, the deformed oscillator and the oblate symmetric top are contained as special solutions. An application of the oblate top limit to the nucleus 12C suggests that the low-lying spectrum can be described as a configuration of three identical alpha particles at the vertices of an equilateral triangle.
Low-lying collective states involving many nucleons interacting by a random ensemble of two-body interactions (TBRE) are investigated in a collective SD-pair subspace, with the collective pairs defined dynamically from the two-nucleon system. It is found that in this truncated pair subspace collective vibrations arise naturally for a general TBRE hamiltonian whereas collective rotations do not. A hamiltonian restricted to include only a few randomly generated separable terms is able to produce collective rotational behavior, as long as it includes a reasonably strong quadrupole-quadrupole component. Similar results arise in the full shell model space. These results suggest that the structure of the hamiltonian is key to producing generic collective rotation.
We study the origin of the regular features obtained in numerical studies of the IBM with random interactions, in particular the dominance of L=0 ground states and the occurrence of vibrational and rotational band structures. It is shown that the geometric shapes associated with IBM Hamiltonians play a crucial role in understanding these regular properties. Different regions of the parameter space are associated with definite geometric shapes, such as spherical and deformed shapes and a condensate of quadrupole bosons.
A new method is introduced to study three-body clusters. Triangular configurations with ${\cal D}_{3h}$ point-group symmetry are analyzed. The spectrum, transition form factors and $B(Eλ)$ values of $^{12}$C are investigated. It is concluded that the low-lying spectrum of $^{12}$C can be described by three alpha-particles at the vertices of an equilateral triangle, but not as a rigid structure. Large rotation-vibration interactions, Coriolis forces and vibration-vibration interactions are needed. Other interpretations, such as the harmonic oscillator and a soft deformed oscillator with SO(6) hyperspherical symmetry, appear to be excluded by electron scattering data.
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.
We investigate the phenomenom of emerging regular spectral features from random interactions. In particular, we address the dominance of L=0 ground states in the context of the vibron model and the interacting boson model. A mean-field analysis links different regions of the parameter space with definite geometric shapes. The results that are, partly, obtained in closed analytic form, provide a clear and transparent interpretation of the distribution of ground state angular momenta as observed before in numerical studies.
We review recent results obtained in numerical studies of the nuclear shell model and the interacting boson model with random interactions, in particular the dominance of ground states with L=0 and the occurrence of vibrational and rotational bands. We discuss some possible explanations of the origin of these regular features.
We investigate the origin of the regular features observed in numerical studies of the interacting boson model with random interactions, in particular the dominance of L=0 ground states and the occurrence of vibrational and rotational band structures. It is shown that all of these properties can be interpreted and explained in terms of a Hartree-Bose mean-field analysis, in which different regions of the parameter space are associated with geometric shapes. The same conclusions hold for the vibron model.
Random interactions are used to investigate to what extent the low-lying behavior of even-even nuclei depend on particular nucleon-nucleon interactions. The surprising results that were obtained for the interacting boson model, i.e. the dominance of ground states with L=0 and the occurrence of both vibrational and rotational structure, are interpreted and explained in terms of a mean-field analysis.
Transfer reactions constitute a stringent test for nuclear supersymmetry, a theory that simultaneously describes neighboring nuclei with bosonic and fermionic character. We construct and analytically evaluate one-nucleon transfer matrix elements between supersymmetric partners with the U(6/4) case as an example, and stress the need for a careful treatment of bosonic and fermionic operators in the construction of mixed tensor operators.
In order to investigate to what extent is the low-lying behavior of even-even nuclei dependent on particular nucleon-nucleon interactions, we consider systems of bosons where these interactions are taken as gaussian random numbers with equal likelyhood of being attractive or repulsive. We find a statistical dominance of L=0 ground states and other correlations, which we analyze in terms of a mean field approach.
In PRL 85, 3773 (2000) it was suggested to use random polynomials to analyze and understand the properties of two-body random ensembles. In this comment we point out that for the vibron model the random polynomial is not quadratic, but has a more general form. We make a comparison for the percentage of ground states with L=0 in the vibron model with random interactions.
We discuss the mass spectrum and strong decays of baryon resonances belonging to the N, Delta, Sigma, Lambda, Xi and Omega families in a collective string-like model for the nucleon. We find good overall agreement with the available data. Systematic discrepancies are found for lowlying S-wave states, in particular in the strong decays of N(1535), N(1650), Sigma(1750), Lambda(1405), Lambda(1670) and Lambda(1800).
We discuss properties of baryon resonances belonging to the Nucleon, Delta, Sigma, Lambda, Xi and Omega families in a collective string-like model for the nucleon, in which the radial excitations are interpreted as rotations and vibrations of the string configuration. We find good overall agreement with the available data. The main discrepancies are found for low lying S-wave states, in particular N(1535), N(1650), Sigma(1750), Lambda*(1405), Lambda(1670) and Lambda(1800).