1,279 research outputs found
Expansion Aspect of Color Transparency on the Lattice
The opportunity to observe color transparency (CT) is determined by how
rapidly a small-sized hadronic wave packet expands. Here we use SU(2) lattice
gauge theory with Wilson fermions in the quenched approximation to investigate
the expansion. The wave packet is modeled by a point hadronic source, often
used as an interpolating field in lattice calculations. The procedure is to
determine the Euclidean time (t), pion channel, Bethe-Salpeter amplitude
, and then evaluate . This quantity represents the soft interaction of a small-sized
wave packet with a pion. The time dependence of is fit as a
superposition of three states, which is found sufficient to reproduce a reduced
size wave packet. Using this superposition allows us to make the analytic
continuation required to study the wave packet expansion in real time. We find
that the matrix elements of the soft interaction between the excited
and ground state decrease rapidly with the energy of the excited state.Comment: 19 pages, latex, 4 figure
Natural Color Transparency in High Energy (p,pp) Reactions
New parameter free calculations including a variety of necessary kinematic
and dynamic effects show that the results of BNL measurements are
consistent with the expectations of color transparency.Comment: latex file, 13 pages, 4 figures appended as ps files, look for "cut
here ..." 1993 Univ. of Washington preprint 404427-00-N93-1
Ground state properties of exotic nuclei near Z=40 in the relativistic mean-field theory,
Study of the ground-state properties of Kr, Sr and Zr isotopes has been
performed in the framework of the relativistic mean field (RMF) theory using
the recently proposed relativistic parameter set NL-SH. It is shown that the
RMF theory provides an unified and excellent description of the binding
energies, isotope shifts and deformation properties of nuclei over a large
range of isospin in the Z=40 region. It is observed that the RMF theory with
the force NL-SH is able to describe the anomalous kinks in isotope shifts in Kr
and Sr nuclei, the problem which has hitherto remained unresolved. This is in
contrast with the density-dependent Skyrme Hartree-Fock approach which does not
reproduce the behaviour of the isotope shifts about shell closure. On the Zr
chain we predict that the isotope shifts exhibit a trend similar to that of the
Kr and Sr nuclei. The RMF theory also predicts shape coexistence in heavy Sr
isotopes. Several dramatic shape transitions in the isotopic chains are shown
to be a general feature of nuclei in this region. A comparison of the
properties with the available mass models shows that the results of the RMF
theory are generally in accord with the predictions of the finite-range droplet
model.Comment: 24 pages Latex, 7 figures (available upon request), Nuclear Physics A
(in press)
The Heumann-Hotzel model for aging revisited
Since its proposition in 1995, the Heumann-Hotzel model has remained as an
obscure model of biological aging. The main arguments used against it were its
apparent inability to describe populations with many age intervals and its
failure to prevent a population extinction when only deleterious mutations are
present. We find that with a simple and minor change in the model these
difficulties can be surmounted. Our numerical simulations show a plethora of
interesting features: the catastrophic senescence, the Gompertz law and that
postponing the reproduction increases the survival probability, as has already
been experimentally confirmed for the Drosophila fly.Comment: 11 pages, 5 figures, to be published in Phys. Rev.
Light Nuclei near Neutron and Proton Drip Lines in the Relativistic Mean-Field Theory
We have made a detailed study of the ground-state properties of nuclei in the
light mass region with atomic numbers Z=10-22 in the framework of the
relativistic mean-field (RMF) theory. The nonlinear model with
scalar self-interaction has been employed. The RMF calculations have been
performed in an axially deformed configuration using the force NL-SH. We have
considered nuclei about the stability line as well as those close to proton and
neutron drip lines. It is shown that the RMF results provide a good agreement
with the available empirical data. The RMF predictions also show a reasonably
good agreement with those of the mass models. It is observed that nuclei in
this mass region are found to possess strong deformations and exhibit shape
changes all along the isotopic chains. The phenomenon of the shape coexistence
is found to persist near the stability line as well as near the drip lines. It
is shown that the magic number N=28 is quenched strongly, thus enabling the
corresponding nuclei to assume strong deformations. Nuclei near the neutron and
proton drip lines in this region are also shown to be strongly deformed.Comment: 49 pages Latex, 12 postscript figures, to appear in Nuclear Physics
Nuclear shadowing at low Q^2
We re-examine the role of vector meson dominance in nuclear shadowing at low
Q^2. We find that models which incorporate both vector meson and partonic
mechanisms are consistent with both the magnitude and the Q^2 slope of the
shadowing data.Comment: 7 pages, 2 figures; to appear in Phys. Rev.
Searching for Color Coherent Effects at Intermediate via Double Scattering Processes
We propose that measuring the dependence of the number of final-state
interactions of the recoil protons in quasi-elastic electron scattering from
light nuclei is a new method to investigate Color Coherent effects at {\bf
intermediate} values of ({ few }). This is instead of
measuring events without final-state interactions. Our calculations indicate
that such measurements could reveal significant color transparency effects for
the highest of the energies initially available at CEBAF. Measurements that
detect more than one hadron in the final state, which require the use of large
acceptance () detectors, are required.Comment: 19 pages in RevTex, 5 postscript figures available from
[email protected]
Nuclear Skins and Halos in the Mean-Field Theory
Nuclei with large neutron-to-proton ratios have neutron skins, which manifest
themselves in an excess of neutrons at distances greater than the radius of the
proton distribution. In addition, some drip-line nuclei develop very extended
halo structures. The neutron halo is a threshold effect; it appears when the
valence neutrons occupy weakly bound orbits. In this study, nuclear skins and
halos are analyzed within the self-consistent Skyrme-Hartree-Fock-Bogoliubov
and relativistic Hartree-Bogoliubov theories for spherical shapes. It is
demonstrated that skins, halos, and surface thickness can be analyzed in a
model-independent way in terms of nucleonic density form factors. Such an
analysis allows for defining a quantitative measure of the halo size. The
systematic behavior of skins, halos, and surface thickness in even-even nuclei
is discussed.Comment: 22 RevTeX pages, 22 EPS figures included, submitted to Physical
Review
Generalized parton distributions and Deeply Virtual Compton Scattering in Color Glass Condensate model
Within the framework of the Color Glass Condensate model, we evaluate quark
and gluon Generalized Parton Distributions (GPDs) and the cross section of
Deeply Virtual Compton Scattering (DVCS) in the small- region. We
demonstrate that the DVCS cross section becomes independent of energy in the
limit of very small , which clearly indicates saturation of the DVCS
cross section. Our predictions for the GPDs and the DVCS cross section at
high-energies can be tested at the future Electron-Ion Collider and in
ultra-peripheral nucleus-nucleus collisions at the LHC.Comment: 20 pages, 8 Figure
Asymmetric nuclear matter:the role of the isovector scalar channel
We try to single out some qualitative new effects of the coupling to the
-isovector-scalar meson introduced in a minimal way in a
phenomenological hadronic field theory. Results for the equation of state
() and the phase diagram of asymmetric nuclear matter () are
discussed. We stress the consistency of the -coupling introduction in a
relativistic approach. New contributions to the slope and curvature of the
symmetry energy and the neutron-proton effective mass splitting appear
particularly interesting. A more repulsive for neutron matter at high
baryon densities is expected. Effects on new critical properties of warm ,
mixing of mechanical and chemical instabilities and isospin distillation, are
also presented. The influence is mostly on the {\it isovectorlike}
collective response.
The results are largely analytical and this makes the physical meaning quite
transparent. Implications for nuclear structure properties of drip-line nuclei
and for reaction dynamics with Radioactive Beams are finally pointed out.Comment: 12 pages, 10 Postscript figure
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