466 research outputs found
Phase Structure of the Interacting Vector Boson Model
The two-fluid Interacting Vector Boson Model (IVBM) with the U(6) as a
dynamical group possesses a rich algebraic structure of physical interesting
subgroups that define its distinct exactly solvable dynamical limits. The
classical images corresponding to different dynamical symmetries are obtained
by means of the coherent state method. The phase structure of the IVBM is
investigated and the following basic phase shapes, connected to a specific
geometric configurations of the ground state, are determined: spherical,
, unstable, O(6), and axially deformed
shape, . The ground state quantum phase transitions
between different phase shapes, corresponding to the different dynamical
symmetries and mixed symmetry case, are investigated.Comment: 9 pages, 10 figure
Algebraic-eikonal approach to medium energy proton scattering from odd-mass nuclei
We extend the algebraic-eikonal approach to medium energy proton scattering
from odd-mass nuclei by combining the eikonal approximation for the scattering
with a description of odd-mass nuclei in terms of the interacting boson-fermion
model. We derive closed expressions for the transition matrix elements for one
of the dynamical symmetries and discuss the interplay between collective and
single-particle degrees of freedom in an application to elastic and inelastic
proton scattering from Pt.Comment: latex, 14 pages, 4 figures uuencoded, to be published in Physical
Review
Algebraic-matrix calculation of vibrational levels of triatomic molecules
We introduce an accurate and efficient algebraic technique for the
computation of the vibrational spectra of triatomic molecules, of both linear
and bent equilibrium geometry. The full three-dimensional potential energy
surface (PES), which can be based on entirely {\it ab initio} data, is
parameterized as a product Morse-cosine expansion, expressed in bond-angle
internal coordinates, and includes explicit interactions among the local modes.
We describe the stretching degrees of freedom in the framework of a Morse-type
expansion on a suitable algebraic basis, which provides exact analytical
expressions for the elements of a sparse Hamiltonian matrix. Likewise, we use a
cosine power expansion on a spherical harmonics basis for the bending degree of
freedom. The resulting matrix representation in the product space is very
sparse and vibrational levels and eigenfunctions can be obtained by efficient
diagonalization techniques. We apply this method to carbonyl sulfide OCS,
hydrogen cyanide HCN, water HO, and nitrogen dioxide NO. When we base
our calculations on high-quality PESs tuned to the experimental data, the
computed spectra are in very good agreement with the observed band origins.Comment: 11 pages, 2 figures, containg additional supporting information in
epaps.ps (results in tables, which are useful but not too important for the
paper
New supersymmetric quartet of nuclei in the A=190 mass region
We present evidence for a new supersymmetric quartet in the A=190 region of
the nuclear mass table. New experimental information on transfer and neutron
capture reactions to the odd-odd nucleaus 194 Ir strongly suggests the
existence of a new supersymmetric quartet, consisting of the 192,193 Os and
193,194 Ir nuclei. We make explicit predictions for the odd-neutron nucleus 193
Os, and suggest that its spectroscopic properties be measured in dedicated
experiments.Comment: 5 pages, 4 figures, updated figures and revised text, Physical Review
C, Rapid Communication, in pres
Unified description of 0+ states in a large class of nuclear collective models
A remarkably simple regularity in the energies of 0+ states in a broad class
of collective models is discussed. A single formula for all 0+ states in
flat-bottomed infinite potentials that depends only on the number of dimensions
and a simpler expression applicable to all three IBA symmetries in the large
boson number limit are presented. Finally, a connection between the energy
expression for 0+ states given by the X(5) model and the predictions of the IBA
near the critical point is explored.Comment: 4 pages, 3 postscript figures, uses revTe
Spectral properties of a tractable collective Hamiltonian
The spectral properties of a tractable collective model Hamiltonian are
studied. The potential energy is truncated up to quartic terms in the
quadrupole deformation variables, incorporating vibrational,
-independent rotational and axially deformed rotational structures.
These physically significant limits are analysed in detail and confronted with
well-established approximation schemes. Furthermore, transitional Hamiltonians
in between the limits are presented and discussed. All results are obtained
within a recently presented Cartan-Weyl based framework to calculate
embedded quadrupole collective observables.Comment: submitted to PR
Consequences of wall stiffness for a beta-soft potential
Modifications of the infinite square well E(5) and X(5) descriptions of
transitional nuclear structure are considered. The eigenproblem for a potential
with linear sloped walls is solved. The consequences of the introduction of
sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Timelike gamma* N -> Delta form factors and Delta Dalitz decay
We extend a covariant model, tested before in the spacelike region for the
physical and lattice QCD regimes, to a calculation of the gamma* N -> Delta
reaction in the timelike region, where the square of the transfered momentum,
q^2, is positive (q^2>0). We estimate the Dalitz decay Delta -> Ne+e- and the
Delta distribution mass distribution function. The results presented here can
be used to simulate the NN -> NNe+e- reactions at moderate beam kinetic
energies.Comment: 14 pages, 11 figure
Sequence of Potentials Interpolating between the U(5) and E(5) Symmetries
It is proved that the potentials of the form (with being
integer) provide a ``bridge'' between the U(5) symmetry of the Bohr Hamiltonian
with a harmonic oscillator potential (occuring for ) and the E(5) model of
Iachello (Bohr Hamiltonian with an infinite well potential, materialized for
infinite ). Parameter-free (up to overall scale factors) predictions for
spectra and B(E2) transition rates are given for the potentials ,
, , corresponding to ratios of 2.093, 2.135,
2.157 respectively, compared to the ratios 2.000 of U(5) and 2.199 of
E(5). Hints about nuclei showing this behaviour, as well as about potentials
``bridging'' the E(5) symmetry with O(6) are briefly discussed. A note about
the appearance of Bessel functions in the framework of E(n) symmetries is given
as a by-product.Comment: LaTeX, 17 pages, 9 postscript figure
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