148 research outputs found
Three-Nucleon Continuum by means of the Hyperspherical Adiabatic Method
This paper investigates the possible use of the Hyperspherical Adiabatic
basis in the description of scattering states of a three-body system. In
particular, we analyze a 1+2 collision process below the three-body breakup.
The convergence patterns for the observables of interest are analyzed by
comparison to a unitary equivalent Hyperspherical Harmonic expansion.
Furthermore, we compare and discuss two different possible choices for
describing the asymptotic configurations of the system, related to the use of
Jacobi or hyperspherical coordinates. In order to illustrate the difficulties
and advantages of the approach two simple numerical applications are shown in
the case of neutron-deuteron scattering at low energies using s-wave
interactions. We found that the optimization driven by the Hyperspherical
Adiabatic basis is not as efficient for scattering states as in bound state
applications.Comment: 29 pages, 5 figures, accepted for publication in Few-Body Systems (in
press
Nuclear Fusion via Triple Collisions in Solar Plasma
We consider several nuclear fusion reactions that take place at the center of
the sun, which are omitted in the standard pp-chain model. More specifically
the reaction rates of the nonradiative production of ^3He, ^7Be, and ^8B nuclei
in triple collisions involving electrons are estimated within the framework of
the adiabatic approximation. These rates are compared with those of the
corresponding binary fusion reactions.Comment: 3 pages, latex (RevTex), no figure
Hyperspherical Description of the Degenerate Fermi Gas: S-wave Interactions
We present a unique theoretical description of the physics of the spherically
trapped -atom degenerate Fermi gas (DFG) at zero temperature based on an
ordinary Schr\"{o}dinger equation with a microscopic, two body interaction
potential. With a careful choice of coordinates and a variational wavefunction,
the many body Schr\"{o}dinger equation can be accurately described by a
\emph{linear}, one dimensional effective Schr\"{o}dinger equation in a single
collective coordinate, the rms radius of the gas. Comparisons of the energy,
rms radius and peak density of ground state energy are made to those predicted
by Hartree-Fock (HF). Also the lowest radial excitation frequency (the
breathing mode frequency) agrees with a sum rule calculation, but deviates from
a HF prediction
Non-perturbative Gluons and Pseudoscalar Mesons in Baryon Spectroscopy
We study baryon spectroscopy including the effects of pseudoscalar meson
exchange and one gluon exchange potentials between quarks, governed by
. The non-perturbative, hyperspherical method calculations show that
one can obtain a good description of the data by using a quark-meson coupling
constant that is compatible with the measured pion-nucleon coupling constant,
and a reasonably small value of .Comment: 12 pages; Submitted to Phys. Rev. C. Rapid Communication
Universality of Regge and vibrational trajectories in a semiclassical model
The orbital and radial excitations of light-light mesons are studied in the
framework of the dominantly orbital state description. The equation of motion
is characterized by a relativistic kinematics supplemented by the usual funnel
potential with a mixed scalar and vector confinement. The influence of finite
quark masses and potential parameters on Regge and vibrational trajectories is
discussed. The case of heavy-light mesons is also presented.Comment: 12 page
Translationally-invariant coupled-cluster method for finite systems
The translational invariant formulation of the coupled-cluster method is
presented here at the complete SUB(2) level for a system of nucleons treated as
bosons. The correlation amplitudes are solution of a non-linear coupled system
of equations. These equations have been solved for light and medium systems,
considering the central but still semi-realistic nucleon-nucleon S3
interaction.Comment: 16 pages, 2 Postscript figures, to be published in Nucl. Phys.
Electromagnetic transition form factors of negative parity nucleon resonances
We have calculated the transition form factors for the electromagnetic
excitation of the negative parity resonances of the nucleon using different
models previously proposed and we discuss their results and limits by
comparison with experimental data.Comment: 13 pages, 6 figures, to be published on Journal of Physics
Generalized sum rules of the nucleon in the constituent quark model
We study the generalized sum rules and polarizabilities of the nucleon in the
framework of the hypercentral constituent quark model. We include in the
calculation all the well known and resonances and consider all the
generalized sum rules for which there are data available. To test the model
dependence of the calculation, we compare our results to the results obtained
in the harmonic oscillator CQM. We furthermore confront our results to the
model-independent sum rules values and to the predictions of the
phenomenological MAID model. The CQM calculations provide a good description of
most of the presented generalized sum rules in the intermediate region
(above GeV) while they encounter difficulties in describing these
observables at low , where the effects of the pion cloud, not included in
the present calculation, are expected to be important.Comment: 26 pages, 10 figure
Spectroscopy of Baryons Containing Two Heavy Quarks in Nonperturbative Quark Dynamics
We have studied the three quark systems in an Effective Hamiltonian approach
in QCD. With only two parameters: the string tension sigma and the strong
coupling constant alpha_s we obtain a good description of the ground state
light and heavy baryons. The prediction of masses of the doubly heavy baryons
not discovered yet are also given. In particular, a mass of 3620 MeV for the
lightest (ccu) baryon is found by employing the hyperspherical formalism to the
three quark confining potential with the string junction.Comment: 8 pages, LaTe
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